Hybrid
Encyclopedia
In biology
and specifically, genetics
, the term hybrid has several meanings, all referring to the offspring of sexual reproduction
.
From a taxonomic
perspective, hybrid refers to offspring resulting from the interbreeding between two animals or plants of different taxa
.
, the word is derived from Latin hybrida , meaning the "offspring of a tame sow and a wild boar", "child of a freeman and slave", etc. The term entered into popular use in English in the 19th century, though examples of its use have been found from the early 17th century.
. The offspring display traits and characteristics of both parents. The offspring of an interspecific cross are very often sterile
; thus, hybrid sterility prevents the movement of genes from one species to the other, keeping both species distinct. Sterility is often attributed to the different number of chromosomes the two species have, for example donkey
s have 62 chromosomes, while horse
s have 64 chromosomes, and mule
s and hinnies
have 63 chromosomes. Mules, hinnies, and other normally sterile interspecific hybrids cannot produce viable gamete
s, because, the extra chromosome cannot make a homologous pair at meiosis
, meiosis is disrupted, and viable sperm and eggs are not formed. However, fertility in female mules has been reported with a donkey as the father.
Most often other processes occurring in plants and animals keep gametic isolation and species distinction. Species often have different mating or courtship patterns or behaviors, the breeding seasons may be distinct and even if mating does occur antigenic reactions to the sperm of other species prevent fertilization or embryo development.
The Lonicera fly
is the first known animal
species
that resulted from natural hybridization. Until the discovery of the Lonicera fly, this process was known to occur in nature only among plant
s
While it is possible to predict the genetic composition of a backcross on average, it is not possible to accurately predict the composition of a particular backcrossed individual, due to random segregation of chromosomes. In a species with two pairs of chromosomes, a twice backcrossed individual would be predicted to contain 12.5% of one species' genome (say, species A). However, it may, in fact, still be a 50% hybrid if the chromosomes from species A were lucky in two successive segregations, and meiotic crossovers happened near the telomere
s. The chance of this is fairly high:
(where the "two times two" comes about from two rounds of meiosis with two chromosomes); however, this probability declines markedly with chromosome number and so the actual composition of a hybrid will be increasingly closer to the predicted composition.
Hybrids are often named by the portmanteau method, combining the names of the two parent species. For example, a zeedonk is a cross between a zebra
and a donkey
. Since the traits of hybrid offspring often vary depending on which species was mother and which was father, it is traditional to use the father's species as the first half of the portmanteau. For example, a liger
is a cross between a male lion
and a female tiger
, while a tiglon
is a cross between a male tiger and a female lion.
in contrast to human controlled selective breeding
or artificial selection
for desirable traits from the human point of view. Normally, these two methods of reproduction operate independently of one another. However, an intermediate form of selective breeding, wherein animals or plants are bred by humans, but with an eye to adaptation to natural region-specific conditions and an acceptance of natural selection to weed out undesirable traits, created many ancient domesticated breeds or types now known as landrace
s.
Many times, domesticated species live in or near areas which also still hold naturally evolved, region-specific wild
ancestor species and subspecies. In some cases, a domesticated species of plant or animal may become feral
, living wild. Other times, a wild species will come into an area inhabited by a domesticated species. Some of these situations lead to the creation of hybridized plants or animals, a cross between the native species and a domesticated one. This type of crossbreeding, termed genetic pollution
by those who are concerned about preserving the genetic base of the wild species, has become a major concern. Hybridization is also a concern to the breeders of purebred species as well, particularly if the gene pool is small and if such crossbreeding or hybridization threatens the genetic base of the domesticated purebred population.
The concern with genetic pollution of a wild population is that hybridized animals and plants may not be as genetically strong as naturally evolved region specific wild ancestors wildlife
which can survive without human husbandry
and have high immunity to natural diseases. The concern of purebred breeders with wildlife hybridizing a domesticated species is that it can coarsen or degrade the specific qualities of a breed developed for a specific purpose, sometimes over many generations. Thus, both purebred breeders and wildlife biologists share a common interest in preventing accidental hybridization.
Hybrids should not be confused with genetic chimeras
such as that between sheep
and goat
known as the geep. Wider interspecific hybrids can be made via in vitro fertilization or somatic hybridization, however the resulting cells are not able to develop into a full organism. An example of interspecific hybrid cell lines is humster
(hamster x human) cells.
with many plant species easily cross pollinating and producing viable seeds, the distinction between each species is often maintained by geographical isolation or differences in the flowering period. Since plants hybridize frequently without much work, they are often created by humans in order to produce improved plants. These improvements can include the production of more or improved; seeds, fruits or other plant parts for consumption, or to make a plant more winter or heat hardy or improve its growth and/or appearance for use in horticulture. Much work is now being done with hybrids to produce more disease resistant plants for both agricultural and horticultural crops. In many groups of plants hybridization has been used to produce larger and more showy flowers and new flower colors.
Many plant genera and species have their origins in polyploidy. Autopolyploidy resulting from the sudden multiplication in the number of chromosomes in typical normal populations caused by unsuccessful separation of the chromosomes during meiosis. Tetraploids or plants with four sets of chromosomes are common in a number of different groups of plants and over time these plants can differentiate into distinct species from the normal diploid line. In Oenothera lamarchiana the diploid species has 14 chromosomes, this species has spontaneously given rise to plants with 28 chromosomes that have been given the name Oenthera gigas. Tetraploids can develop into a breeding population within the diploid population and when hybrids are formed with the diploid population the resulting offspring tend to be sterile triploids, thus effectively stopping the intermixing of genes between the two groups of plants (unless the diploids, in rare cases, produce unreduced gametes).
Another form of polyploidy called allopolyploidy occurs when two different species mate and produce hybrids. Usually the typical chromosome number is doubled in successful allopolyploid species, with four sets of chromosomes the genotypes can sort out to form a complete diploid set from the parent species, thus they can produce fertile offspring that can mate and reproduce with each other but can not back-cross with the parent species. Allopolyploidy in plants often gives them a condition called hybrid vigour, which results in plants that are larger and stronger growing than either of the two parent species. Allopolyploids are often more aggressive growing and can be invaders of new habitats.
Sterility in a hybrid is often a result of chromosome
number; if parents are of differing chromosome pair number, the offspring will have an odd number of chromosomes, leaving them unable to produce chromosomally balanced gametes. While this is a negative in a crop such as wheat
, when growing a crop which produces no seeds would be pointless, it is an attractive attribute in some fruits. Banana
s and seedless watermelon
, for instance, are intentionally bred to be triploid, so that they will produce no seeds. Many hybrids are created by humans, but natural hybrids occur as well.
(heterosis) or heterozygote advantage. A transgressive phenotype
is a phenotype
displaying more extreme characteristics than either of the parent lines. Plant breeders
make use of a number of techniques to produce hybrids, including line breeding and the formation of complex hybrids. An economically important example is hybrid maize
(corn), which provides a considerable seed yield advantage over open pollinated varieties. Hybrid seed dominates the commercial maize seed market in the United States
, Canada
and many other major maize producing countries.
Some natural hybrids are:
Some horticultural hybrids:
s are known where the ranges of two species meet, and hybrids are continually produced in great numbers. These hybrid zones are useful as biological model systems for studying the mechanisms of speciation
(Hybrid speciation
). Recently DNA analysis of a bear shot by a hunter in the North West Territories confirmed the existence of naturally-occurring and fertile grizzly–polar bear hybrids. There have been reports of similar supposed hybrids, but this is the first to be confirmed by DNA analysis. In 1943, Clara Helgason described a male bear shot by hunters during her childhood. It was large and off-white with hair all over its paws. The presence of hair on the bottom of the feet suggests it was a natural hybrid of Kodiak and Polar bear.
and Introduced species
are becoming more widespread. This is allowing another kind of hybridization that is more of the focus of conservation genetics
to occur: anthropogenic hybridization. This anthropogenically caused hybridization increases the challenges in managing certain populations that are experiencing introgression
.
world wide to environments for a long time both directly such as establishing a population to be used as a biological control and indirectly such as accidental escapes of individuals out of agriculture. This causes drastic global affects on various populations with hybridization being one of the reasons introduced species can be so detrimental.
When habitats become broken apart, one of two things can occur, genetically speaking. The first is that populations that were once connected can be cut off from one another, preventing their genes from interacting. Occasionally, this will result in a population of one species breeding with a population of another species as a means of surviving such as the case with the red wolves
. Their population numbers being so small, they needed another means of survival. Habitat fragmentation also led to the influx of generalist species into areas where they would not have been, leading to competition and in some cases interbreeding/incorporation of a population into another. In this way, habitat fragmentation is essentially an indirect method of introducing species to an area.
, hybridization with widespread introgression, and essentially a Hybrid swarm
. Depending on where a population falls along this continuum, the management plans for that population will change. Hybridization is currently an area of great discussion within Wildlife management
and habitat management fields. Global climate change
, which is also anthropogenically caused, is creating other changes such as difference in population distributions which are indirect causes for an increase in anthropogenic hybridization.
then within detection of where a population lies along the hybrid continuum. The dispute of hybridization is how to manage the resulting hybrids. When a population experiences hybridization with substantial introgression, there still exists parent types of each set of individuals. When a complete hybrid swarm is created, all the individuals are hybrids.
In some species, hybridisation plays an important role in evolutionary biology. While most hybrids are disadvantaged
as a result of genetic incompatibility, the fittest survive, regardless of species boundaries. They may have a beneficial combination of traits allowing them to exploit new habitats or to succeed in a marginal habitat where the two parent species are disadvantaged. This has been seen in experiments on sunflower species. Unlike mutation, which affects only one gene, hybridisation creates multiple variations across genes or gene combinations simultaneously. Successful hybrids could evolve into new species within 50-60 generations. This leads some scientists to speculate that life is a genetic continuum rather than a series of self-contained species.
Where there are two closely related species living in the same area, less than 1 in 1000 individuals are likely to be hybrids because animals rarely choose a mate from a different species (otherwise species boundaries would completely break down). In some closely related species there are recognized "hybrid zones".
Some species of Heliconius butterflies exhibit dramatic geographical polymorphism of their wing patterns, which act as aposematic signals advertising their unpalatability to potential predators. Where different-looking geographical races abut, inter-racial hybrids are common, healthy and fertile. Heliconius hybrids can breed with other hybrid individuals and with individuals of either parental race. These hybrid backcrosses are disadvantaged by natural selection because they lack the parental form's warning coloration, and are therefore not avoided by predators.
A similar case in mammals is hybrid White-Tail/Mule Deer. The hybrids don't inherit either parent's escape strategy. White-tail Deer dash while Mule Deer bound. The hybrids are easier prey than the parent species.
In birds, healthy Galapagos Finch hybrids are relatively common, but their beaks are intermediate in shape and less efficient feeding tools than the specialised beaks of the parental species so they lose out in the competition for food. Following a major storm in 1983, the local habitat changed so that new types of plants began to flourish, and in this changed habitat, the hybrids had an advantage over the birds with specialised beaks - demonstrating the role of hybridization in exploiting new ecological niches. If the change in environmental conditions is permanent or is radical enough that the parental species cannot survive, the hybrids become the dominant form. Otherwise, the parental species will re-establish themselves when the environmental change is reversed, and hybrids will remain in the minority.
Natural hybrids may occur when a species is introduced into a new habitat. In Britain, there is hybridisation of native European Red Deer and introduced Chinese Sika Deer. Conservationists want to protect the Red Deer, but the environment favors the Sika Deer genes. There is a similar situation with White-headed Ducks and Ruddy Ducks.
might combine the yellow head of one parent with the orange belly of the other). Most characteristics of the typical hybrid are of one of these two types, and so, in a strict sense, are not really new. However, an intermediate trait does differ from those seen in the parents (e.g., the pink flowers of the intermediate hybrid just mentioned are not seen in either of its parents). Likewise, combined traits are new when viewed as a combination.
In a hybrid, any trait that falls outside the range of parental variation is termed heterotic
. Heterotic hybrids do have new traits, that is, they are not intermediate. Positive heterosis produces more robust hybrids, they might be stronger or bigger; while the term negative heterosis refers to weaker or smaller hybrids. Heterosis is common in both animal and plant hybrids. For example, hybrids between a lion and a tigress ("ligers") are much larger than either of the two progenitors, while a tigon (lioness × tiger) is smaller. Also the hybrids between the Common Pheasant (Phasianus colchicus) and domestic fowl (Gallus gallus) are larger than either of their parents, as are those produced between the Common Pheasant and hen Golden Pheasant (Chrysolophus pictus). Spurs are absent in hybrids of the former type, although present in both parents.
When populations hybridize, often the first generation (F1) hybrids are very uniform. Typically, however, the individual members of subsequent hybrid generations are quite variable. High levels of variability in a natural population, then, are indicative of hybridity. Researchers use this fact to ascertain whether a population is of hybrid origin. Since such variability generally occurs only in later hybrid generations, the existence of variable hybrids is also an indication that the hybrids in question are fertile.
s can be threatened with extinction
when new allele
s or genes are introduced that alter that ecotype. This is sometimes called genetic mixing. Hybridization and introgression
of new genetic material can lead to the replacement of local genotypes if the hybrids are more fit
and have breeding advantages over the indigenous ecotype or species. These hybridization events can result from the introduction of non native genotypes by humans or through habitat modification, bringing previously isolated species into contact. Genetic mixing can be especially detrimental for rare species in isolated habitats, ultimately affecting the population to such a degree that none of the originally genetically distinct population remains.
, the Green Revolution
's use of conventional hybridization increased yields by breeding "high-yielding varieties". The replacement of locally indigenous breeds, compounded with unintentional cross-pollination and crossbreeding (genetic mixing), has reduced the gene pools of various wild and indigenous breeds resulting in the loss of genetic diversity
. Since the indigenous breeds are often well-adapted to local extremes in climate and have immunity to local pathogens this can be a significant genetic erosion
of the gene pool for future breeding. Therefore, commercial plant geneticists strive to breed "widely adapted" cultivars to counteract this tendency.
In plants, barriers to hybridization include blooming period differences, different pollinator vectors, inhibition of pollen tube growth, somatoplastic sterility, cytoplasmic-genic male sterility and structural differences of the chromosomes.
as the offspring of a griffin
and a horse
, and the Minotaur
which is the offspring of Pasiphaë
and a white bull). More often they are kind of chimera
, i.e., a composite of the physical attributes of two or more kinds of animals, mythical beasts, and often humans, with no suggestion that they are the result of interbreeding, e.g., Harpies, mermaid
s, and centaurs.
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
and specifically, genetics
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
, the term hybrid has several meanings, all referring to the offspring of sexual reproduction
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
.
- In general usage, hybrid is synonymous with heterozygous: any offspring resulting from the mating of two distinctly homozygous individuals
- a genetic hybrid carries two different alleleAlleleAn allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
s of the same geneGeneA gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains... - a structural hybrid results from the fusion of gameteGameteA gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s that have differing structure in at least one chromosomeChromosomeA chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
, as a result of structural abnormalities - a numerical hybrid results from the fusion of gametes having different haploid numbers of chromosomesPloidyPloidy is the number of sets of chromosomes in a biological cell.Human sex cells have one complete set of chromosomes from the male or female parent. Sex cells, also called gametes, combine to produce somatic cells. Somatic cells, therefore, have twice as many chromosomes. The haploid number is...
- a permanent hybrid is a situation where only the heterozygous genotypeGenotypeThe genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
occurs, because all homozygous combinations are lethal.
From a taxonomic
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
perspective, hybrid refers to offspring resulting from the interbreeding between two animals or plants of different taxa
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
.
- Hybrids between different subspeciesSubspeciesSubspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
within a species (such as between the Bengal tigerBengal TigerThe Bengal tiger is a tiger subspecies native to the Indian subcontinent that in 2010 has been classified as endangered by IUCN...
and Siberian tiger) are known as intra-specific hybrids. Hybrids between different species within the same genus (such as between lions and tigers) are sometimes known as interspecific hybrids or crosses. Hybrids between different genera (such as between sheepDomestic sheepSheep are quadrupedal, ruminant mammals typically kept as livestock. Like all ruminants, sheep are members of the order Artiodactyla, the even-toed ungulates. Although the name "sheep" applies to many species in the genus Ovis, in everyday usage it almost always refers to Ovis aries...
and goatGoatThe domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...
s) are known as intergeneric hybrids. Extremely rare interfamilial hybrids have been known to occur (such as the guineafowl hybrids). No interordinal (between different orders) animal hybrids are known. - The second type of hybrid consists of crosses between populationPopulationA population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
s, breedBreedA breed is a group of domestic animals or plants with a homogeneous appearance, behavior, and other characteristics that distinguish it from other animals or plants of the same species. Despite the centrality of the idea of "breeds" to animal husbandry, there is no scientifically accepted...
s or cultivarCultivarA cultivar'Cultivar has two meanings as explained under Formal definition. When used in reference to a taxon, the word does not apply to an individual plant but to all those plants sharing the unique characteristics that define the cultivar. is a plant or group of plants selected for desirable...
s within a single species. This meaning is often used in plant and animal breeding, where hybrids are commonly produced and selected because they have desirable characteristics not found or inconsistently present in the parent individuals or populations. This flow of genetic material between populations or races is often called hybridization.
Etymology
According to the Oxford English DictionaryOxford English Dictionary
The Oxford English Dictionary , published by the Oxford University Press, is the self-styled premier dictionary of the English language. Two fully bound print editions of the OED have been published under its current name, in 1928 and 1989. The first edition was published in twelve volumes , and...
, the word is derived from Latin hybrida , meaning the "offspring of a tame sow and a wild boar", "child of a freeman and slave", etc. The term entered into popular use in English in the 19th century, though examples of its use have been found from the early 17th century.
Types of hybrids
Depending on the parents, there are a number of different types of hybrids;- Single cross hybrids — result from the cross between two true breeding organismTrue breeding organismA true breeding organism, sometimes also called a pure-bred, is an organism having certain biological traits which are passed on to all subsequent generations when bred with another true breeding organism for the same traits...
s and produces an F1 generation called an F1 hybridF1 hybridF1 hybrid is a term used in genetics and selective breeding. F1 stands for Filial 1, the first filial generation seeds/plants or animal offspring resulting from a cross mating of distinctly different parental types....
(F1 is short for Filial 1, meaning "first offspring"). The cross between two different homozygous lines produces an F1 hybrid that is heterozygous; having two alleles, one contributed by each parent and typically one is dominant and the other recessive. The F1 generation is also phenotypicallyPhenotypeA phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
homogeneous, producing offspring that are all similar to each other. - Double cross hybrids — result from the cross between two different F1 hybrids.
- Three-way cross hybrids — result from the cross between one parent that is an F1 hybrid and the other is from an inbred line.
- Triple cross hybrids — result from the crossing of two different three-way cross hybrids.
- Population hybrids — result from the crossing of plants or animals in a populationPopulationA population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
with another population. These include crosses between organisms such as interspecific hybrids or crosses between different races.
Interspecific hybrids
Interspecific hybrids are bred by mating two species, normally from within the same genusGenus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
. The offspring display traits and characteristics of both parents. The offspring of an interspecific cross are very often sterile
Sterility (physiology)
Sterility is the physiological inability to effect sexual reproduction in a living thing, members of whose kind have been produced sexually. The term may be used in reference to* types of organism, such as the mule, a sterile hybrid;...
; thus, hybrid sterility prevents the movement of genes from one species to the other, keeping both species distinct. Sterility is often attributed to the different number of chromosomes the two species have, for example donkey
Donkey
The donkey or ass, Equus africanus asinus, is a domesticated member of the Equidae or horse family. The wild ancestor of the donkey is the African Wild Ass, E...
s have 62 chromosomes, while horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s have 64 chromosomes, and mule
Mule
A mule is the offspring of a male donkey and a female horse. Horses and donkeys are different species, with different numbers of chromosomes. Of the two F1 hybrids between these two species, a mule is easier to obtain than a hinny...
s and hinnies
Hinny
A hinny is a domestic equine hybrid that is the offspring of a male horse and a female donkey . It is similar to the more common mule, which is the product of a female horse and a male donkey....
have 63 chromosomes. Mules, hinnies, and other normally sterile interspecific hybrids cannot produce viable gamete
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s, because, the extra chromosome cannot make a homologous pair at meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
, meiosis is disrupted, and viable sperm and eggs are not formed. However, fertility in female mules has been reported with a donkey as the father.
Most often other processes occurring in plants and animals keep gametic isolation and species distinction. Species often have different mating or courtship patterns or behaviors, the breeding seasons may be distinct and even if mating does occur antigenic reactions to the sperm of other species prevent fertilization or embryo development.
The Lonicera fly
Lonicera fly
The Lonicera fly, a hybrid in the genus Rhagoletis, is a North American fruit fly of the family Tephritidae. Its larvae feed on the berries of species of introduced honeysuckle that were brought to America within the last 250 years as ornamental plants...
is the first known animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
that resulted from natural hybridization. Until the discovery of the Lonicera fly, this process was known to occur in nature only among plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s
While it is possible to predict the genetic composition of a backcross on average, it is not possible to accurately predict the composition of a particular backcrossed individual, due to random segregation of chromosomes. In a species with two pairs of chromosomes, a twice backcrossed individual would be predicted to contain 12.5% of one species' genome (say, species A). However, it may, in fact, still be a 50% hybrid if the chromosomes from species A were lucky in two successive segregations, and meiotic crossovers happened near the telomere
Telomere
A telomere is a region of repetitive DNA sequences at the end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes. Its name is derived from the Greek nouns telos "end" and merοs "part"...
s. The chance of this is fairly high:
(where the "two times two" comes about from two rounds of meiosis with two chromosomes); however, this probability declines markedly with chromosome number and so the actual composition of a hybrid will be increasingly closer to the predicted composition.Hybrids are often named by the portmanteau method, combining the names of the two parent species. For example, a zeedonk is a cross between a zebra
Zebra
Zebras are several species of African equids united by their distinctive black and white stripes. Their stripes come in different patterns unique to each individual. They are generally social animals that live in small harems to large herds...
and a donkey
Donkey
The donkey or ass, Equus africanus asinus, is a domesticated member of the Equidae or horse family. The wild ancestor of the donkey is the African Wild Ass, E...
. Since the traits of hybrid offspring often vary depending on which species was mother and which was father, it is traditional to use the father's species as the first half of the portmanteau. For example, a liger
Liger
The liger is a hybrid cross between a male lion and a tigress . Thus, it has parents with the same genus but of different species. It is distinct from the similar hybrid tiglon. It is the largest of all known cats and extant felines.Ligers enjoy swimming, which is a characteristic of tigers, and...
is a cross between a male lion
Lion
The lion is one of the four big cats in the genus Panthera, and a member of the family Felidae. With some males exceeding 250 kg in weight, it is the second-largest living cat after the tiger...
and a female tiger
Tiger
The tiger is the largest cat species, reaching a total body length of up to and weighing up to . Their most recognizable feature is a pattern of dark vertical stripes on reddish-orange fur with lighter underparts...
, while a tiglon
Tiglon
A tiglon , tigon, and tion is a hybrid cross between a male tiger and a lioness . Thus, it has parents with the same genus but of different species. The tiglon is not currently as common as the converse hybrid, the liger; however, in the late 19th and early 20th centuries, tiglons were more...
is a cross between a male tiger and a female lion.
Domestic and wild hybrids
Hybrids between domesticated and wild animals in particular may be problematic. Breeders of domesticated species discourage crossbreeding with wild species, unless a deliberate decision is made to incorporate a trait of a wild ancestor back into a given breed or strain. Wild populations of animals and plants have evolved naturally over millions of years through a process of natural selectionNatural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
in contrast to human controlled selective breeding
Selective breeding
Selective breeding is the process of breeding plants and animals for particular genetic traits. Typically, strains that are selectively bred are domesticated, and the breeding is sometimes done by a professional breeder. Bred animals are known as breeds, while bred plants are known as varieties,...
or artificial selection
Artificial selection
Artificial selection describes intentional breeding for certain traits, or combination of traits. The term was utilized by Charles Darwin in contrast to natural selection, in which the differential reproduction of organisms with certain traits is attributed to improved survival or reproductive...
for desirable traits from the human point of view. Normally, these two methods of reproduction operate independently of one another. However, an intermediate form of selective breeding, wherein animals or plants are bred by humans, but with an eye to adaptation to natural region-specific conditions and an acceptance of natural selection to weed out undesirable traits, created many ancient domesticated breeds or types now known as landrace
Landrace
A landrace is a local variety of a domesticated animal or plant species which has developed largely by natural processes, by adaptation to the natural and cultural environment in which it lives. It differs from a formal breed which has been bred deliberately to conform to a particular standard...
s.
Many times, domesticated species live in or near areas which also still hold naturally evolved, region-specific wild
Wildlife
Wildlife includes all non-domesticated plants, animals and other organisms. Domesticating wild plant and animal species for human benefit has occurred many times all over the planet, and has a major impact on the environment, both positive and negative....
ancestor species and subspecies. In some cases, a domesticated species of plant or animal may become feral
Feral
A feral organism is one that has changed from being domesticated to being wild or untamed. In the case of plants it is a movement from cultivated to uncultivated or controlled to volunteer. The introduction of feral animals or plants to their non-native regions, like any introduced species, may...
, living wild. Other times, a wild species will come into an area inhabited by a domesticated species. Some of these situations lead to the creation of hybridized plants or animals, a cross between the native species and a domesticated one. This type of crossbreeding, termed genetic pollution
Genetic pollution
Genetic pollution is a controversial term for uncontrolled gene flow into wild populations. This gene flow is undesirable according to some environmentalists and conservationists, including groups such as Greenpeace, TRAFFIC, and GeneWatch UK.-Usage:...
by those who are concerned about preserving the genetic base of the wild species, has become a major concern. Hybridization is also a concern to the breeders of purebred species as well, particularly if the gene pool is small and if such crossbreeding or hybridization threatens the genetic base of the domesticated purebred population.
The concern with genetic pollution of a wild population is that hybridized animals and plants may not be as genetically strong as naturally evolved region specific wild ancestors wildlife
Wildlife
Wildlife includes all non-domesticated plants, animals and other organisms. Domesticating wild plant and animal species for human benefit has occurred many times all over the planet, and has a major impact on the environment, both positive and negative....
which can survive without human husbandry
Animal husbandry
Animal husbandry is the agricultural practice of breeding and raising livestock.- History :Animal husbandry has been practiced for thousands of years, since the first domestication of animals....
and have high immunity to natural diseases. The concern of purebred breeders with wildlife hybridizing a domesticated species is that it can coarsen or degrade the specific qualities of a breed developed for a specific purpose, sometimes over many generations. Thus, both purebred breeders and wildlife biologists share a common interest in preventing accidental hybridization.
Examples of hybrid animals
- Hybrid IguanaHybrid IguanaThe Hybrid Iguana is a first generation hybrid, the result of intergeneric breeding between a male Marine Iguana and a female Land Iguana on South Plaza Island in the Galápagos Islands where the territories of the two species overlap.- Anatomy and morphology:Marine Iguanas have sharp claws and...
, a single‐cross hybrid resulting from natural interbreeding between maleMaleMale refers to the biological sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilization...
marine iguanaMarine iguanaThe Marine Iguana is an iguana found only on the Galápagos Islands that has the ability, unique among modern lizards, to live and forage in the sea, making it a marine reptile. The Iguana can dive over 30 ft into the water. It has spread to all the islands in the archipelago, and is...
s and femaleFemaleFemale is the sex of an organism, or a part of an organism, which produces non-mobile ova .- Defining characteristics :The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male...
land iguanaGalapagos Land IguanaThe Galapagos Land Iguana is a species of lizard in the Iguanidae family. It is one of three species of the genus Conolophus...
s since the late 2000s. - Equid hybrids
- MuleMuleA mule is the offspring of a male donkey and a female horse. Horses and donkeys are different species, with different numbers of chromosomes. Of the two F1 hybrids between these two species, a mule is easier to obtain than a hinny...
, a cross of female horseHorseThe horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
and a male donkeyDonkeyThe donkey or ass, Equus africanus asinus, is a domesticated member of the Equidae or horse family. The wild ancestor of the donkey is the African Wild Ass, E...
. - HinnyHinnyA hinny is a domestic equine hybrid that is the offspring of a male horse and a female donkey . It is similar to the more common mule, which is the product of a female horse and a male donkey....
, a cross between a female donkey and a male horse. MuleMuleA mule is the offspring of a male donkey and a female horse. Horses and donkeys are different species, with different numbers of chromosomes. Of the two F1 hybrids between these two species, a mule is easier to obtain than a hinny...
and hinnyHinnyA hinny is a domestic equine hybrid that is the offspring of a male horse and a female donkey . It is similar to the more common mule, which is the product of a female horse and a male donkey....
are examples of reciprocal hybrids. - ZebroidZebroidA zebroid is the offspring of any cross between a zebra and any other equine: essentially, a zebra hybrid. In most cases, the sire is a zebra stallion. Offspring of a donkey sire and zebra dam, called a zebra hinny, or donkra, do exist but are rare. Zebroids have been bred since the 19th century...
s- Zeedonk or Zonkey, a zebraZebraZebras are several species of African equids united by their distinctive black and white stripes. Their stripes come in different patterns unique to each individual. They are generally social animals that live in small harems to large herds...
/donkeyDonkeyThe donkey or ass, Equus africanus asinus, is a domesticated member of the Equidae or horse family. The wild ancestor of the donkey is the African Wild Ass, E...
cross. - Zorse, a zebra/horse cross
- Zony or Zetland, a zebra/ponyPonyA pony is a small horse . Depending on context, a pony may be a horse that is under an approximate or exact height at the withers, or a small horse with a specific conformation and temperament. There are many different breeds...
cross ("zony" is a generic term; "zetland" is specifically a hybrid of the Shetland pony breed with a zebra)
- Zeedonk or Zonkey, a zebra
- Mule
- Bovid hybridBovid hybridA bovid hybrid is a hybrid of two different members of the bovid family.-Bison/Domestic cattle hybrids:The American bison and European bison have been hybridized with Domestic Cattle. With wisent, this was originally done in an attempt to reinvigorate the declining wisent population...
s- DzoDzoA dzo is a hybrid of yak and domestic cattle. The word dzo technically refers to a male hybrid, while a female is known as a dzomo or zhom. Alternative Romanizations of the Tibetan names include zho and zo. In Mongolian it is called khainag...
, zo or yakow; a cross between a domestic cow/bullCattleCattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
and a yakYakThe yak, Bos grunniens or Bos mutus, is a long-haired bovine found throughout the Himalayan region of south Central Asia, the Tibetan Plateau and as far north as Mongolia and Russia. In addition to a large domestic population, there is a small, vulnerable wild yak population...
. - BeefaloBeefaloBeefalo are a fertile hybrid offspring of domestic cattle, Bos taurus, and the American bison, Bison bison...
, a cross of an American bisonAmerican BisonThe American bison , also commonly known as the American buffalo, is a North American species of bison that once roamed the grasslands of North America in massive herds...
and a domestic cowCattleCattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
. This is a fertile breed; this along with genetic evidence has caused them to be recently reclassified into the same genus, Bos. - ZubronZubronŻubroń is a hybrid of domestic cattle and wisent. The wisent is the European bison; hence, the żubroń is analogous to the American beefalo...
, a hybrid between wisentWisentThe wisent , Bison bonasus, also known as the European bison or European wood bison, is a species of Eurasian bison. It is the heaviest surviving land animal in Europe; a typical wisent is about long, not counting a tail of long, and tall. Weight typically can range from , with an occasional big...
(European bison) and domestic cowCattleCattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
.
- Dzo
- Sheep-goat hybridSheep-goat hybridA sheep–goat hybrid is the hybrid offspring of a sheep and a goat. Although sheep and goats seem similar and can be mated, they belong to different genera in the subfamily Caprinae of the family Bovidae. Sheep belong to the genus Ovis and have 54 chromosomes, while goats belong to the genus Capra...
s, such as the Toast of Botswana. - Ursid hybridUrsid hybridAn ursid hybrid is an animal with parents from two different species or subspecies of the Ursidae family. Species and subspecies of bear known to have produced offspring with another bear species or subspecies include brown bears, black bears, grizzly bears and polar bears, all of which are...
s, such as the grizzly-polar bear hybridGrizzly-polar bear hybridA grizzly–polar bear hybrid is a rare ursid hybrid that has occurred both in captivity and in the wild. In 2006, the occurrence of this hybrid in nature was confirmed by testing the DNA for a strange-looking bear that had been shot near Sachs Harbour, Northwest Territories on Banks Island in the...
, occur between black bears, brown bears, and polar bears. - Felid hybridFelid hybridThere are a number of hybrids between various felid species. This article deals with hybrids between the smaller felid species and those between smaller felids and Panthera species. For hybrids between two Panthera species see Panthera hybrid.-Servical/caraval:A servical is a cross between a...
s- Savannah catsSavannah (cat)The Savannah is a domestic hybrid cat breed. It is a cross between a serval and a domestic cat. -History:...
are the hybrid cross between an African serval catServalThe serval , Leptailurus serval or Caracal serval, known in Afrikaans as Tierboskat, "tiger-forest-cat", is a medium-sized African wild cat. DNA studies have shown that the serval is closely related to the African golden cat and the caracal...
and a domestic cat - A hybrid between a Bengal tigerBengal TigerThe Bengal tiger is a tiger subspecies native to the Indian subcontinent that in 2010 has been classified as endangered by IUCN...
and a Siberian tiger is an example of an intra-specific hybrid. - LigerLigerThe liger is a hybrid cross between a male lion and a tigress . Thus, it has parents with the same genus but of different species. It is distinct from the similar hybrid tiglon. It is the largest of all known cats and extant felines.Ligers enjoy swimming, which is a characteristic of tigers, and...
s and TiglonTiglonA tiglon , tigon, and tion is a hybrid cross between a male tiger and a lioness . Thus, it has parents with the same genus but of different species. The tiglon is not currently as common as the converse hybrid, the liger; however, in the late 19th and early 20th centuries, tiglons were more...
s (crosses between a lionLionThe lion is one of the four big cats in the genus Panthera, and a member of the family Felidae. With some males exceeding 250 kg in weight, it is the second-largest living cat after the tiger...
and a tigerTigerThe tiger is the largest cat species, reaching a total body length of up to and weighing up to . Their most recognizable feature is a pattern of dark vertical stripes on reddish-orange fur with lighter underparts...
) and other Panthera hybridPanthera hybridThe four living species of Panthera genus may produce a number of hybrid crosses...
s such as the lijagulepLijagulepA Congolese Spotted Lion or more correctly lijagulep is the hybrid of a male lion and female jaguar-leopard . Several lijaguleps have been bred, but only one appears to have been exhibited as a Congolese Spotted Lion...
. Various other wild cat crosses are known involving the lynxLynxA lynx is any of the four Lynx genus species of medium-sized wildcats. The name "lynx" originated in Middle English via Latin from Greek word "λύγξ", derived from the Indo-European root "*leuk-", meaning "light, brightness", in reference to the luminescence of its reflective eyes...
, bobcatBobcatThe bobcat is a North American mammal of the cat family Felidae, appearing during the Irvingtonian stage of around 1.8 million years ago . With twelve recognized subspecies, it ranges from southern Canada to northern Mexico, including most of the continental United States...
, leopardLeopardThe leopard , Panthera pardus, is a member of the Felidae family and the smallest of the four "big cats" in the genus Panthera, the other three being the tiger, lion, and jaguar. The leopard was once distributed across eastern and southern Asia and Africa, from Siberia to South Africa, but its...
, servalServalThe serval , Leptailurus serval or Caracal serval, known in Afrikaans as Tierboskat, "tiger-forest-cat", is a medium-sized African wild cat. DNA studies have shown that the serval is closely related to the African golden cat and the caracal...
, etc. - Bengal catBengal CatBengal Cat may refer to:*Leopard Cat*Bengal , a domestic cat breed...
, a cross between the Asian leopard catLeopard CatThe leopard cat is a small wild cat of South and East Asia. Since 2002 it has been listed as Least Concern by IUCN as it is widely distributed but threatened by habitat loss and hunting in parts of its range...
and the domestic cat, one of many hybrids between the domestic cat and wild cat species. The domestic catCatThe cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...
, African wild cat and European wildcat may be considered variant populations of the same species (Felis silvestris), making such crosses non-hybrids.
- Savannah cats
- Fertile canid hybridCanid hybridCanid hybrids are the result of interbreeding between different species of the canine family -Genetic considerations:Members of the dog genus Canis: wolves, dogs , coyotes, and golden jackals cannot interbreed with members of the wider dog family: the Canidae, such as South American canids, foxes,...
s occur between coyoteCoyoteThe coyote , also known as the American jackal or the prairie wolf, is a species of canine found throughout North and Central America, ranging from Panama in the south, north through Mexico, the United States and Canada...
s, wolves, dingoDingoThe Australian Dingo or Warrigal is a free-roaming wild dog unique to the continent of Australia, mainly found in the outback. Its original ancestors are thought to have arrived with humans from southeast Asia thousands of years ago, when dogs were still relatively undomesticated and closer to...
es, jackalJackalAlthough the word jackal has been historically used to refer to many small- to medium-sized species of the wolf genus of mammals, Canis, today it most properly and commonly refers to three species: the black-backed jackal and the side-striped jackal of sub-Saharan Africa, and the golden jackal of...
s and domestic dogsDogThe domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
. - Hybrids between blackBlack RhinocerosThe Black Rhinoceros or Hook-lipped Rhinoceros , is a species of rhinoceros, native to the eastern and central areas of Africa including Kenya, Tanzania, Cameroon, South Africa, Namibia, Zimbabwe, and Angola...
and white rhinocerosWhite RhinocerosThe White Rhinoceros or Square-lipped rhinoceros is one of the five species of rhinoceros that still exist. It has a wide mouth used for grazing and is the most social of all rhino species...
es have been recognized. - Hybrids between spotted owlSpotted OwlThe Spotted Owl, Strix occidentalis, is a species of true owl. It is a resident species of forests in western North America, where it nests in tree holes, old bird of prey nests, or rock crevices. Nests can be between 13 and 66 yards high and usually contain two eggs...
s and barred owlBarred OwlThe Barred Owl is a large typical owl. It goes by many other names, including eight hooter, rain owl, wood owl, and striped owl, but is probably best known as the hoot owl.-Description:...
s - CamaCama (animal)A cama is a hybrid between a male dromedary camel and a female llama, produced via artificial insemination at the Camel Reproduction Centre in Dubai. The first cama was born on January 14, 1998...
, a cross between a camelCamelA camel is an even-toed ungulate within the genus Camelus, bearing distinctive fatty deposits known as humps on its back. There are two species of camels: the dromedary or Arabian camel has a single hump, and the bactrian has two humps. Dromedaries are native to the dry desert areas of West Asia,...
and a llamaLlamaThe llama is a South American camelid, widely used as a meat and pack animal by Andean cultures since pre-Hispanic times....
, also an intergeneric hybrid. - Wholphin, a fertile but very rare cross between a false killer whaleFalse Killer WhaleThe False Killer Whale is a cetacean, and the third largest member of the oceanic dolphin family . It lives in temperate and tropical waters throughout the world. As its name implies, the False Killer Whale shares characteristics, such as appearance, with the more widely known Orca...
and a bottlenose dolphinBottlenose DolphinBottlenose dolphins, the genus Tursiops, are the most common and well-known members of the family Delphinidae, the family of oceanic dolphins. Recent molecular studies show the genus contains two species, the common bottlenose dolphin and the Indo-Pacific bottlenose dolphin , instead of one...
. - A fertile cross between a king snakeKing SnakeKing Snake is a fictional character who appears in books published by DC Comics universe, usually as an adversary of Tim Drake and Batman. Created by writer Chuck Dixon and artist Tom Lyle, King Snake first appeared in Robin #2...
and a corn snakeCorn SnakeThe Corn Snake , or Red Rat Snake, is a North American species of Rat Snake that subdues its small prey by constriction. The name "Corn Snake" is a holdover from the days when southern farmers stored harvested ears of corn in a wood frame or log building called a crib...
. - At Chester ZooChester ZooChester Zoo is a zoological garden at Upton-by-Chester, in Cheshire, England. It was opened in 1931 by George Mottershead and his family, who used as a basis some animals reported to have come from an earlier zoo in Shavington. It is one of the UK's largest zoos at...
in the United Kingdom, a cross between an African elephant (male) and an Asian elephantAsian ElephantThe Asian or Asiatic elephant is the only living species of the genus Elephas and distributed in Southeast Asia from India in the west to Borneo in the east. Three subspecies are recognized — Elephas maximus maximus from Sri Lanka, the Indian elephant or E. m. indicus from mainland Asia, and E. m....
(female). The male calf was named Harjeeven. It died of intestinal infection after twelve days. - Cagebird breeders sometimes breed hybrids between species of finchFinchThe true finches are passerine birds in the family Fringillidae. They are predominantly seed-eating songbirds. Most are native to the Northern Hemisphere, but one subfamily is endemic to the Neotropics, one to the Hawaiian Islands, and one subfamily – monotypic at genus level – is found...
, such as goldfinchCarduelisThe genus Carduelisis a large group of birds in the finch family Fringillidae. It includes the greenfinches, redpolls, goldfinches, linnets, the twite, and the non-African siskins...
x canaryDomestic CanaryThe Domestic Canary, often simply known as the canary, is a domesticated form of the wild Canary, a small songbird in the finch family originating from the Macaronesian Islands ....
. These birds are known as mules. - Gamebird hybridsGamebird hybridsGamebird hybrids are the result of crossing species of game birds, including ducks, with each other and with domestic poultry. These hybrid species may occur both naturally or though the intervention of man....
, hybrids between gamebirds and domestic fowl, including chickens, guineafowlGuineafowlThe guineafowl are a family of birds in the Galliformes order, although some authorities include the guineafowl as a subfamily, Numidinae, of the family Phasianidae...
and peafowlPeafowlPeafowl are two Asiatic species of flying birds in the genus Pavo of the pheasant family, Phasianidae, best known for the male's extravagant eye-spotted tail, which it displays as part of courtship. The male is called a peacock, the female a peahen, and the offspring peachicks. The adult female...
, interfamilial hybrids. - Numerous macawMacawMacaws are small to large, often colourful New World parrots. Of the many different Psittacidae genera, six are classified as macaws: Ara, Anodorhynchus, Cyanopsitta, Primolius, Orthopsittaca, and Diopsittaca...
hybrids are also known. - Red kiteRed KiteThe Red Kite is a medium-large bird of prey in the family Accipitridae, which also includes many other diurnal raptors such as eagles, buzzards, and harriers. The species is currently endemic to the Western Palearctic region in Europe and northwest Africa, though formerly also occurred just...
x black kiteBlack KiteThe Black Kite is a medium-sized bird of prey in the family Accipitridae, which also includes many other diurnal raptors. Unlike others of the group, they are opportunistic hunters and are more likely to scavenge. They spend a lot of time soaring and gliding in thermals in search of food. Their...
: five bred unintentionally at a falconryFalconryFalconry is "the taking of wild quarry in its natural state and habitat by means of a trained raptor". There are two traditional terms used to describe a person involved in falconry: a falconer flies a falcon; an austringer flies a hawk or an eagle...
center in England. (It is reported that the black kite (the male) refused female black kites but mated with two female red kites.) - Hybridization between the endemic Cuban crocodileCuban crocodileThe Cuban crocodile is a small species of crocodile found only in Cuba's Zapata Swamp and the Isle of Youth, and highly endangered, though it formerly ranged elsewhere in the Caribbean...
(Crocodilus rhombifer) and the widely distributed American crocodileAmerican CrocodileThe American crocodile is a species of crocodilian found in the Neotropics. It is the most widespread of the four extant species of crocodiles from the Americas. Populations occur from the Atlantic and Pacific coasts of southern Mexico to South America as far as Peru and Venezuela. It also lives...
(Crocodilus acutus) is causing conservation problems for the former species as a threat to its genetic integrity. - Saltwater crocodileSaltwater CrocodileThe saltwater crocodile, also known as estuarine or Indo-Pacific crocodile, is the largest of all living reptiles...
s (Crocodylus porosus) have mated with Siamese crocodileSiamese CrocodileSiamese crocodile is a freshwater crocodile native to Indonesia , Brunei, East Malaysia, Laos, Cambodia, Burma, Thailand, and Vietnam...
s (Crocodylus siamensis) in captivity producing offspring which in many cases have grown over 20 feet (6 meters) in length. It is likely that wild hybridization occurred historically in parts of southeast Asia. - Blood parrot cichlid, which is probably created by crossing a red head cihclid and a Midas cichlid or red devil cichlid
- The mulardMulardThe Mulard is a hybrid variety of domestic duck produced by crossing a female Pekin with a male Muscovy Duck. Since the domestic Pekin is descended from the Mallard Duck and the Muscovy is a separate species, all Mulards are sterile F1 hybrids...
duck, hybrid of the domestic pekin duckPekin duckPekin duck, or Long Island duck , is a breed of domesticated duck used primarily for egg and meat production. It was bred from the Mallard in China. The ancestors of those ducks originated from the canals which linked waterways in Nanjing and originally had small bodies and black feathers...
and domesticated muscovy duckMuscovy DuckThe Muscovy Duck is a large duck which is native to Mexico and Central and South America. A small wild population reaches into the United States in the lower Rio Grande Valley of Texas...
s. - Killer beesAfricanized beeAfricanized honey bees, known colloquially as "killer bees", are a hybrid variety of the European honeybee , generated by a man-made breeding of the African honey bee, A. m. scutellata, with various European honey bees such as the Italian bee A. m. ligustica and A. m. iberiensis. These bees are far...
were created in an attempt to breed tamer and more manageable bees. This was done by crossing a european honey beeEuropean honey beeThe Western honey bee or European honey bee is a species of honey bee. The genus Apis is Latin for "bee", and mellifera comes from Latin melli- "honey" and ferre "to bear"—hence the scientific name means "honey-bearing bee"...
and an african beeAfrican beeThe African honey bee is a subspecies of the Western honey bee. It is native to central and southern Africa, though at the southern extreme it is replaced by the Cape honey bee, Apis mellifera capensis....
, but instead the offspring became more aggressive and highly defensive bees that had escaped into the wild. - In Australia, New Zealand and other areas where the Pacific Black DuckPacific Black DuckThe Pacific Black Duck is a dabbling duck found in much of Indonesia, New Guinea, Australia, New Zealand, and many islands in the southwestern Pacific, reaching to the Caroline Islands in the north and French Polynesia in the east. It is usually called the Grey Duck in New Zealand...
occurs, it is hybridised by the much more aggressive introduced MallardMallardThe Mallard , or Wild Duck , is a dabbling duck which breeds throughout the temperate and subtropical Americas, Europe, Asia, and North Africa, and has been introduced to New Zealand and Australia....
. This is a concern to wildlife authorities throughout the affected area, as it is seen as Genetic pollutionGenetic pollutionGenetic pollution is a controversial term for uncontrolled gene flow into wild populations. This gene flow is undesirable according to some environmentalists and conservationists, including groups such as Greenpeace, TRAFFIC, and GeneWatch UK.-Usage:...
of the Black Duck gene pool.
Hybrids should not be confused with genetic chimeras
Chimera (genetics)
A chimera or chimaera is a single organism that is composed of two or more different populations of genetically distinct cells that originated from different zygotes involved in sexual reproduction. If the different cells have emerged from the same zygote, the organism is called a mosaic...
such as that between sheep
Domestic sheep
Sheep are quadrupedal, ruminant mammals typically kept as livestock. Like all ruminants, sheep are members of the order Artiodactyla, the even-toed ungulates. Although the name "sheep" applies to many species in the genus Ovis, in everyday usage it almost always refers to Ovis aries...
and goat
Goat
The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...
known as the geep. Wider interspecific hybrids can be made via in vitro fertilization or somatic hybridization, however the resulting cells are not able to develop into a full organism. An example of interspecific hybrid cell lines is humster
Humster
A humster is a hybrid cell line made from hamster oocyte fertilized with human sperm routinely created for mainly two reasons:* To avoid legal issues with working with pure human embryonic stem cell lines....
(hamster x human) cells.
Hybrid plants
Plant species hybridize more readily than animal species, and the resulting hybrids are more often fertile hybrids and may reproduce, though there still exist sterile hybrids and selective hybrid elimination where the offspring are less able to survive and are thus eliminated before they can reproduce. A number of plant species are the result of hybridization and polyploidyPolyploidy
Polyploid is a term used to describe cells and organisms containing more than two paired sets of chromosomes. Most eukaryotic species are diploid, meaning they have two sets of chromosomes — one set inherited from each parent. However polyploidy is found in some organisms and is especially common...
with many plant species easily cross pollinating and producing viable seeds, the distinction between each species is often maintained by geographical isolation or differences in the flowering period. Since plants hybridize frequently without much work, they are often created by humans in order to produce improved plants. These improvements can include the production of more or improved; seeds, fruits or other plant parts for consumption, or to make a plant more winter or heat hardy or improve its growth and/or appearance for use in horticulture. Much work is now being done with hybrids to produce more disease resistant plants for both agricultural and horticultural crops. In many groups of plants hybridization has been used to produce larger and more showy flowers and new flower colors.
Another form of polyploidy called allopolyploidy occurs when two different species mate and produce hybrids. Usually the typical chromosome number is doubled in successful allopolyploid species, with four sets of chromosomes the genotypes can sort out to form a complete diploid set from the parent species, thus they can produce fertile offspring that can mate and reproduce with each other but can not back-cross with the parent species. Allopolyploidy in plants often gives them a condition called hybrid vigour, which results in plants that are larger and stronger growing than either of the two parent species. Allopolyploids are often more aggressive growing and can be invaders of new habitats.
Sterility in a hybrid is often a result of chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
number; if parents are of differing chromosome pair number, the offspring will have an odd number of chromosomes, leaving them unable to produce chromosomally balanced gametes. While this is a negative in a crop such as wheat
Wheat
Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
, when growing a crop which produces no seeds would be pointless, it is an attractive attribute in some fruits. Banana
Banana
Banana is the common name for herbaceous plants of the genus Musa and for the fruit they produce. Bananas come in a variety of sizes and colors when ripe, including yellow, purple, and red....
s and seedless watermelon
Watermelon
Watermelon is a vine-like flowering plant originally from southern Africa. Its fruit, which is also called watermelon, is a special kind referred to by botanists as a pepo, a berry which has a thick rind and fleshy center...
, for instance, are intentionally bred to be triploid, so that they will produce no seeds. Many hybrids are created by humans, but natural hybrids occur as well.
Heterosis
Hybrids are sometimes stronger than either parent variety, a phenomenon most common with plant hybrids, which when present is known as hybrid vigorHeterosis
Heterosis, or hybrid vigor, or outbreeding enhancement, is the improved or increased function of any biological quality in a hybrid offspring. The adjective derived from heterosis is heterotic....
(heterosis) or heterozygote advantage. A transgressive phenotype
Transgressive segregation
In genetics, transgressive segregation is the formation of extreme phenotypes, or transgressive phenotypes, observed in segregated hybrid populations compared to phenotypes observed in the parental lines....
is a phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
displaying more extreme characteristics than either of the parent lines. Plant breeders
Plant breeding
Plant breeding is the art and science of changing the genetics of plants in order to produce desired characteristics. Plant breeding can be accomplished through many different techniques ranging from simply selecting plants with desirable characteristics for propagation, to more complex molecular...
make use of a number of techniques to produce hybrids, including line breeding and the formation of complex hybrids. An economically important example is hybrid maize
Maize
Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...
(corn), which provides a considerable seed yield advantage over open pollinated varieties. Hybrid seed dominates the commercial maize seed market in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
and many other major maize producing countries.
Examples of species hybrids
Some plant hybrids include:- Leyland cypressLeyland CypressThe Leyland Cypress, × Cupressocyparis leylandii , often referred to as just Leylandii, is a fast-growing evergreen tree much used in horticulture, primarily for hedges and screens. Even on sites of relatively poor culture, plants have been known to grow to heights of 15 metres in 16 years...
, [x Cupressocyparis leylandii] hybrid between Monterey Cypress and Nootka Cypress. - LimequatLimequatThe limequat is a citrus tree that is the result of a cross between the Key lime and the kumquat, hybridized by Dr. Walter Swingle in 1909.-Description:...
, limeLime (fruit)Lime is a term referring to a number of different citrus fruits, both species and hybrids, which are typically round, green to yellow in color, 3–6 cm in diameter, and containing sour and acidic pulp. Limes are a good source of vitamin C. Limes are often used to accent the flavors of foods and...
and kumquatKumquatCumquats or kumquats are a group of small fruit-bearing trees in the flowering plant family Rutaceae, either forming the genus Fortunella, or placed within Citrus sensu lato...
hybrid. - LoganberryLoganberryThe loganberry is an hexaploid hybrid produced from crossing an octaploid blackberry and a diploid red raspberry. The plant and the fruit resemble the blackberry more than the raspberry, but the fruit colour is a dark red, rather than black...
, a hybrid between raspberryRaspberryThe raspberry or hindberry is the edible fruit of a multitude of plant species in the genus Rubus, most of which are in the subgenus Idaeobatus; the name also applies to these plants themselves...
and blackberryBlackberryThe blackberry is an edible fruit produced by any of several species in the Rubus genus of the Rosaceae family. The fruit is not a true berry; botanically it is termed an aggregate fruit, composed of small drupelets. The plants typically have biennial canes and perennial roots. Blackberries and...
. - London planeLondon PlanePlatanus × acerifolia, the London plane, London planetree, or hybrid plane, is a tree in the genus Platanus. It is usually thought to be a hybrid of Platanus orientalis and the Platanus occidentalis . Some authorities think that it may be a cultivar of P...
, a hybrid between Platanus orientalis Oriental planePlatanus orientalisPlatanus orientalis, or the Oriental plane, is a large, deciduous tree of the Platanaceae family, known for its longevity and spreading crown. The species name derives from its historical distribution eastward from the Balkans, where it was recognized in ancient Greek history and literature....
and Platanus occidentalis American planeAmerican sycamorePlatanus occidentalis, also known as American Sycamore, American plane, Occidental plane, and Buttonwood, is one of the species of Platanus native to North America...
(American sycamore). Thus forming [Platanus x acerifolia] - Magnolia × albaMagnolia × albaMagnolia × alba, commonly known as the white champaca, is a flowering plant of hybrid origin found nowhere in the wild and cultivated for ornamental use...
, an interspecific hybrid between Magnolia champaca and Magnolia montanaMagnolia montanaMagnolia montana is a species of Magnolia native to the Western Malesia region of the Indomalaya ecozone.- See also :*Magnolia × alba*Magnolia champaca*Michelia-External links:* from the Magnolia Society.*... - PeppermintPeppermintPeppermint is a hybrid mint, a cross between the watermint and spearmint . The plant, indigenous to Europe, is now widespread in cultivation throughout all regions of the world...
, a hybrid between spearmintSpearmintMentha spicata syn. M. cordifolia is a species of mint native to much of Europe and southwest Asia, though its exact natural range is uncertain due to extensive early cultivation. It grows in wet soils...
and water mintWater mintMentha aquatica is a perennial plant in the genus Mentha native throughout Europe except for the extreme north, and also northwest Africa and southwest Asia....
. - TangeloTangeloThe tangelo , Citrus × tangelo, is also widely known as the honeybell. Tangelo is a citrus fruit that is a hybrid of a tangerine and either a pomelo or a grapefruit. The fruits are the size of an adult fist and have a tangerine taste, but are very juicy, to the point of not providing much flesh...
, a hybrid of a Mandarin orangeMandarin orangeThe orange, also known as the ' or mandarine , is a small citrus tree with fruit resembling other oranges. Mandarin oranges are usually eaten plain or in fruit salads...
and a pomeloPomeloThe pomelo is a citrus fruit native to Southeast Asia. It is usually pale green to yellow when ripe, with sweet white flesh and very thick albedo . It is the largest citrus fruit, 15–25 cm in diameter, and usually weighing 1–2 kg...
which may have been developed in Asia about 3,500 years ago. - TriticaleTriticaleTriticale is a hybrid of wheat and rye first bred in laboratories during the late 19th century. The grain was originally bred in Scotland and Sweden. Commercially available triticale is almost always a second generation hybrid, i.e., a cross between two kinds of primary triticales...
, a wheatWheatWheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
–ryeRyeRye is a grass grown extensively as a grain and as a forage crop. It is a member of the wheat tribe and is closely related to barley and wheat. Rye grain is used for flour, rye bread, rye beer, some whiskeys, some vodkas, and animal fodder...
hybrid. - WheatWheatWheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
; most modern and ancient wheat breeds are themselves hybrids. Bread wheat is a hexaploid hybrid of three wild grasses; durumDurumDurum wheat or macaroni wheat is the only tetraploid species of wheat of commercial importance that is widely cultivated today...
(pasta) wheat is a tetraploid hybrid of two wild grasses. - Triangle of UTriangle of UThe Triangle of U is a theory about the evolution and relationships between members of the plant genus Brassica. The theory states that the genomes of three ancestral species of Brassica combined to create three of the common contemporary vegetables and oilseed crop species...
: cabbage, mustard etc. - GrapefruitGrapefruitThe grapefruit , is a subtropical citrus tree known for its sour fruit, an 18th-century hybrid first bred in Barbados. When found, it was named the "forbidden fruit"; it has also been misidentified with the pomelo or shaddock , one of the parents of this hybrid, the other being sweet orange The...
, hybrid between a pomeloPomeloThe pomelo is a citrus fruit native to Southeast Asia. It is usually pale green to yellow when ripe, with sweet white flesh and very thick albedo . It is the largest citrus fruit, 15–25 cm in diameter, and usually weighing 1–2 kg...
and the Jamaican sweet orangeOrange (fruit)An orange—specifically, the sweet orange—is the citrus Citrus × sinensis and its fruit. It is the most commonly grown tree fruit in the world....
.
Some natural hybrids are:
- Iris albicansIris albicansIris albicans, also known as the Cemetery Iris, White Cemetery Iris, or the White Flag Iris, is a species of iris which was planted on graves in Muslim regions and grows in many countries throughout the Middle East and northern Africa. It was later introduced to Spain, and then other European...
, a sterile hybrid which spreads by rhizome division - Evening primroseOenotheraOenothera is a Genus of about 125 species of annual, biennial and perennial herbaceous flowering plants, native to North and South America. It is the type genus of the family Onagraceae, the Evening Primrose Family. Common names include evening-primrose, suncups, and sundrops.The species vary in...
, a flower which was the subject of famous experiments by Hugo de VriesHugo de VriesHugo Marie de Vries ForMemRS was a Dutch botanist and one of the first geneticists. He is known chiefly for suggesting the concept of genes, rediscovering the laws of heredity in the 1890s while unaware of Gregor Mendel's work, for introducing the term "mutation", and for developing a mutation...
on polyploidyPolyploidyPolyploid is a term used to describe cells and organisms containing more than two paired sets of chromosomes. Most eukaryotic species are diploid, meaning they have two sets of chromosomes — one set inherited from each parent. However polyploidy is found in some organisms and is especially common...
and diploidy.
Some horticultural hybrids:
- Dianthus x allwoodii, is a hybrid between Dianthus caryophyllus × Dianthus plumarius. This is an "interspecific hybrid" or hybrid between two species in the same genus.
- x Heucherella tiarelloides, or Heuchera sanguinea × Tiarella cordifolia is an "intergeneric hybrid" a hybrid between two different genera.
- Quercus x warei [Quercus robur x Quercus bicolor] Kindred Spirit Hybrid OakKindred Spirit Hybrid OakKindred Spirit Hybrid Oak is an oak hybrid of Quercus robur x Quercus bicolor thus forming a Quercus x warei. In lay terms this means an Upright English Oak was hybridized with a Swamp White Oak and this tree was one of the progeny. The proper name of this tree is Quercus x warei 'Nadler'...
Hybrids in nature
Hybridisation between two closely related species is actually a common occurrence in nature but is also being greatly influenced by anthropogenic changes as well. Hybridization is a naturally occurring genetic process where individuals from two genetically distinct populations mate. As stated above, it can occur both intraspecifically, between different distinct populations within the same species, and interspecifically, between two different species. Hybrids can be either sterile/not viable or viable/fertile. This affects the kind of effect that this hybrid will have on its and other populations that it interacts with. Many hybrid zoneHybrid zone
A hybrid zone exists where the ranges of two interbreeding species meet. For a hybrid zone to be stable, the offspring produced by the cross have to be less fit than members of the parent species, although this condition does not need to be met in the very first hybrid generation...
s are known where the ranges of two species meet, and hybrids are continually produced in great numbers. These hybrid zones are useful as biological model systems for studying the mechanisms of speciation
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
(Hybrid speciation
Hybrid speciation
Hybrid speciation is the process wherein hybridization between two different closely related species leads to a distinct phenotype. This phenotype in very rare cases can also be fitter than the parental lineage and as such natural selection may then favor these individuals. Eventually, if...
). Recently DNA analysis of a bear shot by a hunter in the North West Territories confirmed the existence of naturally-occurring and fertile grizzly–polar bear hybrids. There have been reports of similar supposed hybrids, but this is the first to be confirmed by DNA analysis. In 1943, Clara Helgason described a male bear shot by hunters during her childhood. It was large and off-white with hair all over its paws. The presence of hair on the bottom of the feet suggests it was a natural hybrid of Kodiak and Polar bear.
Anthropogenic hybridization
Anthropogenic caused changes to the environment such as fragmentationHabitat fragmentation
Habitat fragmentation as the name implies, describes the emergence of discontinuities in an organism's preferred environment , causing population fragmentation...
and Introduced species
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...
are becoming more widespread. This is allowing another kind of hybridization that is more of the focus of conservation genetics
Conservation genetics
Conservation genetics is an interdisciplinary science that aims to apply genetic methods to the conservation and restoration of biodiversity. Researchers involved in conservation genetics come from a variety of fields including population genetics, molecular ecology, biology, evolutionary biology,...
to occur: anthropogenic hybridization. This anthropogenically caused hybridization increases the challenges in managing certain populations that are experiencing introgression
Introgression
Introgression, also known as introgressive hybridization, in genetics is the movement of a gene from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species...
.
Introduced species and habitat fragmentation
Humans have been introducing speciesIntroduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...
world wide to environments for a long time both directly such as establishing a population to be used as a biological control and indirectly such as accidental escapes of individuals out of agriculture. This causes drastic global affects on various populations with hybridization being one of the reasons introduced species can be so detrimental.
When habitats become broken apart, one of two things can occur, genetically speaking. The first is that populations that were once connected can be cut off from one another, preventing their genes from interacting. Occasionally, this will result in a population of one species breeding with a population of another species as a means of surviving such as the case with the red wolves
Red Wolf
The red wolf is a North American canid which once roamed throughout the Southeastern United States and is a glacial period survivor of the Late Pleistocene epoch...
. Their population numbers being so small, they needed another means of survival. Habitat fragmentation also led to the influx of generalist species into areas where they would not have been, leading to competition and in some cases interbreeding/incorporation of a population into another. In this way, habitat fragmentation is essentially an indirect method of introducing species to an area.
The hybridization continuum
There is a kind of continuum with three semi-distinct categories dealing with anthropogenic hybridization: hybridization without IntrogressionIntrogression
Introgression, also known as introgressive hybridization, in genetics is the movement of a gene from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species...
, hybridization with widespread introgression, and essentially a Hybrid swarm
Hybrid swarm
A hybrid swarm is a population of hybrids that has survived beyond the initial hybrid generation, with interbreeding between hybrid individuals and backcrossing with its parent types. Such population are highly variable, with the genetic and phenetic characteristics of individuals ranging widely...
. Depending on where a population falls along this continuum, the management plans for that population will change. Hybridization is currently an area of great discussion within Wildlife management
Wildlife management
Wildlife management attempts to balance the needs of wildlife with the needs of people using the best available science. Wildlife management can include game keeping, wildlife conservation and pest control...
and habitat management fields. Global climate change
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
, which is also anthropogenically caused, is creating other changes such as difference in population distributions which are indirect causes for an increase in anthropogenic hybridization.
Consequences
Hybridization can be a less discussed way toward ExtinctionExtinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
then within detection of where a population lies along the hybrid continuum. The dispute of hybridization is how to manage the resulting hybrids. When a population experiences hybridization with substantial introgression, there still exists parent types of each set of individuals. When a complete hybrid swarm is created, all the individuals are hybrids.
Management of hybrids
Conservationists disagree on when is the proper time to give up on a population that is becoming a hybrid swarm or to try and save the still existing pure individuals. Once it becomes a complete mixture, we should look to conserve those hybrids to avoid their loss. Most leave it as a case-by-case basis, depending on detecting of hybrids within the group. It is nearly impossible to regulate hybridization via policy because hybridization can occur beneficially when it occurs "naturally" and there is the matter of protecting those previously mentioned hybrid swarms because if they are the only remaining evidence of prior species, they need to be conserved as well.In some species, hybridisation plays an important role in evolutionary biology. While most hybrids are disadvantaged
Disadvantaged
The "disadvantaged" is a generic term for individuals or groups of people who:* Face special problems such as physical or mental disability * Lack money or economic support....
as a result of genetic incompatibility, the fittest survive, regardless of species boundaries. They may have a beneficial combination of traits allowing them to exploit new habitats or to succeed in a marginal habitat where the two parent species are disadvantaged. This has been seen in experiments on sunflower species. Unlike mutation, which affects only one gene, hybridisation creates multiple variations across genes or gene combinations simultaneously. Successful hybrids could evolve into new species within 50-60 generations. This leads some scientists to speculate that life is a genetic continuum rather than a series of self-contained species.
Where there are two closely related species living in the same area, less than 1 in 1000 individuals are likely to be hybrids because animals rarely choose a mate from a different species (otherwise species boundaries would completely break down). In some closely related species there are recognized "hybrid zones".
Some species of Heliconius butterflies exhibit dramatic geographical polymorphism of their wing patterns, which act as aposematic signals advertising their unpalatability to potential predators. Where different-looking geographical races abut, inter-racial hybrids are common, healthy and fertile. Heliconius hybrids can breed with other hybrid individuals and with individuals of either parental race. These hybrid backcrosses are disadvantaged by natural selection because they lack the parental form's warning coloration, and are therefore not avoided by predators.
A similar case in mammals is hybrid White-Tail/Mule Deer. The hybrids don't inherit either parent's escape strategy. White-tail Deer dash while Mule Deer bound. The hybrids are easier prey than the parent species.
In birds, healthy Galapagos Finch hybrids are relatively common, but their beaks are intermediate in shape and less efficient feeding tools than the specialised beaks of the parental species so they lose out in the competition for food. Following a major storm in 1983, the local habitat changed so that new types of plants began to flourish, and in this changed habitat, the hybrids had an advantage over the birds with specialised beaks - demonstrating the role of hybridization in exploiting new ecological niches. If the change in environmental conditions is permanent or is radical enough that the parental species cannot survive, the hybrids become the dominant form. Otherwise, the parental species will re-establish themselves when the environmental change is reversed, and hybrids will remain in the minority.
Natural hybrids may occur when a species is introduced into a new habitat. In Britain, there is hybridisation of native European Red Deer and introduced Chinese Sika Deer. Conservationists want to protect the Red Deer, but the environment favors the Sika Deer genes. There is a similar situation with White-headed Ducks and Ruddy Ducks.
Expression of parental traits in hybrids
When two distinct types of organisms breed with each other, the resulting hybrids typically have intermediate traits (e.g., one parent has red flowers, the other has white, and the hybrid, pink flowers). Commonly, hybrids also combine traits seen only separately in one parent or the other (e.g., a bird hybridBird hybrid
A bird hybrid is a bird that has two different species as parents. The resulting bird can present with any combination of characters from the parent species, from totally identical to completely different. Usually, the bird hybrid shows intermediate characteristics between the two species...
might combine the yellow head of one parent with the orange belly of the other). Most characteristics of the typical hybrid are of one of these two types, and so, in a strict sense, are not really new. However, an intermediate trait does differ from those seen in the parents (e.g., the pink flowers of the intermediate hybrid just mentioned are not seen in either of its parents). Likewise, combined traits are new when viewed as a combination.
In a hybrid, any trait that falls outside the range of parental variation is termed heterotic
Heterosis
Heterosis, or hybrid vigor, or outbreeding enhancement, is the improved or increased function of any biological quality in a hybrid offspring. The adjective derived from heterosis is heterotic....
. Heterotic hybrids do have new traits, that is, they are not intermediate. Positive heterosis produces more robust hybrids, they might be stronger or bigger; while the term negative heterosis refers to weaker or smaller hybrids. Heterosis is common in both animal and plant hybrids. For example, hybrids between a lion and a tigress ("ligers") are much larger than either of the two progenitors, while a tigon (lioness × tiger) is smaller. Also the hybrids between the Common Pheasant (Phasianus colchicus) and domestic fowl (Gallus gallus) are larger than either of their parents, as are those produced between the Common Pheasant and hen Golden Pheasant (Chrysolophus pictus). Spurs are absent in hybrids of the former type, although present in both parents.
When populations hybridize, often the first generation (F1) hybrids are very uniform. Typically, however, the individual members of subsequent hybrid generations are quite variable. High levels of variability in a natural population, then, are indicative of hybridity. Researchers use this fact to ascertain whether a population is of hybrid origin. Since such variability generally occurs only in later hybrid generations, the existence of variable hybrids is also an indication that the hybrids in question are fertile.
Genetic mixing and extinction
Regionally developed ecotypeEcotype
In evolutionary ecology, an ecotype,Greek: οίκος = home and τύπος = type, coined by Göte Turesson in 1922 sometimes called ecospecies, describes a genetically distinct geographic variety, population or race within species , which is adapted to specific environmental conditions.Typically, ecotypes...
s can be threatened with extinction
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
when new allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
s or genes are introduced that alter that ecotype. This is sometimes called genetic mixing. Hybridization and introgression
Introgression
Introgression, also known as introgressive hybridization, in genetics is the movement of a gene from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species...
of new genetic material can lead to the replacement of local genotypes if the hybrids are more fit
Fitness (biology)
Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
and have breeding advantages over the indigenous ecotype or species. These hybridization events can result from the introduction of non native genotypes by humans or through habitat modification, bringing previously isolated species into contact. Genetic mixing can be especially detrimental for rare species in isolated habitats, ultimately affecting the population to such a degree that none of the originally genetically distinct population remains.
Effect on biodiversity and food security
In agriculture and animal husbandryAnimal husbandry
Animal husbandry is the agricultural practice of breeding and raising livestock.- History :Animal husbandry has been practiced for thousands of years, since the first domestication of animals....
, the Green Revolution
Green Revolution
Green Revolution refers to a series of research, development, and technology transfer initiatives, occurring between the 1940s and the late 1970s, that increased agriculture production around the world, beginning most markedly in the late 1960s....
's use of conventional hybridization increased yields by breeding "high-yielding varieties". The replacement of locally indigenous breeds, compounded with unintentional cross-pollination and crossbreeding (genetic mixing), has reduced the gene pools of various wild and indigenous breeds resulting in the loss of genetic diversity
Genetic diversity
Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....
. Since the indigenous breeds are often well-adapted to local extremes in climate and have immunity to local pathogens this can be a significant genetic erosion
Genetic erosion
Genetic erosion is a process whereby an already limited gene pool of an endangered species of plant or animal diminishes even more when individuals from the surviving population die off without getting a chance to meet and breed with others in their endangered low population.Genetic erosion occurs...
of the gene pool for future breeding. Therefore, commercial plant geneticists strive to breed "widely adapted" cultivars to counteract this tendency.
Limiting factors
A number of conditions exist that limit the success of hybridization, the most obvious is great genetic diversity between most species. But in animals and plants that are more closely related hybridization barriers can include morphological differences, differing times of fertility, mating behaviors and cues, physiological rejection of sperm cells or the developing embryo.In plants, barriers to hybridization include blooming period differences, different pollinator vectors, inhibition of pollen tube growth, somatoplastic sterility, cytoplasmic-genic male sterility and structural differences of the chromosomes.
Mythical and legendary hybrids
Ancient folktales often contain mythological creatures, sometimes these are described as hybrids (e.g., HippogriffHippogriff
A Hippogriff is a legendary creature, supposedly the offspring of a griffin and a mare.- Early references :...
as the offspring of a griffin
Griffin
The griffin, griffon, or gryphon is a legendary creature with the body of a lion and the head and wings of an eagle...
and a horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
, and the Minotaur
Minotaur
In Greek mythology, the Minotaur , as the Greeks imagined him, was a creature with the head of a bull on the body of a man or, as described by Roman poet Ovid, "part man and part bull"...
which is the offspring of Pasiphaë
Pasiphaë
In Greek mythology, Pasiphaë , "wide-shining" was the daughter of Helios, the Sun, by the eldest of the Oceanids, Perse; Like her doublet Europa, her origins were in the East, in her case at Colchis, the palace of the Sun; she was given in marriage to King Minos of Crete. With Minos, she was the...
and a white bull). More often they are kind of chimera
Chimera (mythology)
The Chimera or Chimaera was, according to Greek mythology, a monstrous fire-breathing female creature of Lycia in Asia Minor, composed of the parts of multiple animals: upon the body of a lioness with a tail that ended in a snake's head, the head of a goat arose on her back at the center of her...
, i.e., a composite of the physical attributes of two or more kinds of animals, mythical beasts, and often humans, with no suggestion that they are the result of interbreeding, e.g., Harpies, mermaid
Mermaid
A mermaid is a mythological aquatic creature with a female human head, arms, and torso and the tail of a fish. A male version of a mermaid is known as a "merman" and in general both males and females are known as "merfolk"...
s, and centaurs.
External links
- Artificial Hybridisation - Artificial Hybridisation in orchids
- Domestic Fowl Hybrids
- Hybrid Mammals
- Hybridisation in animals Evolution Revolution: Two Species Become One, Study Says (nationalgeographic.com)
- Hybrids of wildcats with domestic cats
- Scientists Create Butterfly Hybrid - Creation of new species through hybridization was thought to be common only in plants, and rare in animals.
- What is a human admixed embryo?
- Video of Mirror carp & Gold fish spawning at a fishing venue in France