Outcrossing
Encyclopedia
Outcrossing is the practice of introducing unrelated genetic material into a breeding line. It increases genetic diversity
, thus reducing the probability of all individuals being subject to disease or reducing genetic abnormalities(only within the first generation). It actually can serve to increase the number of individuals who carry a disease recessively.
It is used in line-breeding to restore vigor or size and fertility to a breeding line. "Line-breeding", is where animals carry a common ancestor in their pedigrees and are bred together, should be considered distinct from the term "in-breeding" which is the production of offspring by parents more closely related than the average.
Outcrossing is now the norm of most purposeful breeding, contrary to what is commonly believed.
The outcrossing breeder intends to remove the traits by using "new blood". With dominant traits, one can still see the expression of the traits and can remove those traits whether one outcrosses, line breeds or inbreds. With recessives, outcrossing allows for the recessive traits to migrate across a population. It may actually increase the number of individuals carrying a disease. The outcrossing breeder then may have individuals that have many deleterious genes that are expressed by placing their animals against a similarly outcrossed individual. There is now a gamut of deleterious genes within each individual in many breeds. However one may increase the variance of genes within the gene pool by outcrossing, protecting against extinction by a single stressor from the environment. In cats, there is currently a study running to determine the genetic diversity within the cat breeds.
Outcrossing is believed to be the "norm" in the wild. However, it is not logical as migration occurs by necessity. Feral cats, for example are one of the most inbred as individuals remain nearby their original homes, unless environmental stresses drive them to migration.
Breeders inbreed
within their genetic pool, attempting to maintain desirable traits and to cull those traits that are undesirable. When undesirable traits begin to appear, breedings are selected to determine if a trait is recessive or dominant. Removal is accomplished by breeding two individuals of known genetic status, usually they are related.
In nature, where breeding is not managed, outcrossing rates may be estimated by genetic analysis, by employing mathematical models of mating system
s such as the mixed mating model
or the effective selfing model
. This allows calculation of the amount of genetic exchange between populations, and thus provides insights into the biogeography
and phytogeography
of species.
Gregor Mendel
used outcrossing in his experiments with flowers for his breeding stock. He then used the resulting offspring to chart inheritance patterns, using the crossing of siblings, and backcrossing to parents to determine how inheritance functioned.
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....
, thus reducing the probability of all individuals being subject to disease or reducing genetic abnormalities(only within the first generation). It actually can serve to increase the number of individuals who carry a disease recessively.
It is used in line-breeding to restore vigor or size and fertility to a breeding line. "Line-breeding", is where animals carry a common ancestor in their pedigrees and are bred together, should be considered distinct from the term "in-breeding" which is the production of offspring by parents more closely related than the average.
Outcrossing is now the norm of most purposeful breeding, contrary to what is commonly believed.
The outcrossing breeder intends to remove the traits by using "new blood". With dominant traits, one can still see the expression of the traits and can remove those traits whether one outcrosses, line breeds or inbreds. With recessives, outcrossing allows for the recessive traits to migrate across a population. It may actually increase the number of individuals carrying a disease. The outcrossing breeder then may have individuals that have many deleterious genes that are expressed by placing their animals against a similarly outcrossed individual. There is now a gamut of deleterious genes within each individual in many breeds. However one may increase the variance of genes within the gene pool by outcrossing, protecting against extinction by a single stressor from the environment. In cats, there is currently a study running to determine the genetic diversity within the cat breeds.
Outcrossing is believed to be the "norm" in the wild. However, it is not logical as migration occurs by necessity. Feral cats, for example are one of the most inbred as individuals remain nearby their original homes, unless environmental stresses drive them to migration.
Breeders inbreed
Inbreeding
Inbreeding is the reproduction from the mating of two genetically related parents. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is...
within their genetic pool, attempting to maintain desirable traits and to cull those traits that are undesirable. When undesirable traits begin to appear, breedings are selected to determine if a trait is recessive or dominant. Removal is accomplished by breeding two individuals of known genetic status, usually they are related.
In nature, where breeding is not managed, outcrossing rates may be estimated by genetic analysis, by employing mathematical models of mating system
Mating system
A mating system is a way in which a group is structured in relation to sexual behaviour. The precise meaning depends upon the context. With respect to higher animals, it specifies which males mate with which females, under which circumstances; recognised animal mating systems include monogamy,...
s such as the mixed mating model
Mixed mating model
The mixed mating model is a mathematical model that describes the mating system of a plant population in terms of the degree of self-fertilisation present. It is a fairly simplistic model, employing several simplifying assumptions, most notably the assumption that every fertilisation event may be...
or the effective selfing model
Effective selfing model
The effective selfing model is a mathematical model that describes the mating system of a plant population in terms of the degree of self-fertilisation present....
. This allows calculation of the amount of genetic exchange between populations, and thus provides insights into the biogeography
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...
and phytogeography
Phytogeography
Phytogeography , also called geobotany, is the branch of biogeography that is concerned with the geographic distribution of plant species...
of species.
Gregor Mendel
Gregor Mendel
Gregor Johann Mendel was an Austrian scientist and Augustinian friar who gained posthumous fame as the founder of the new science of genetics. Mendel demonstrated that the inheritance of certain traits in pea plants follows particular patterns, now referred to as the laws of Mendelian inheritance...
used outcrossing in his experiments with flowers for his breeding stock. He then used the resulting offspring to chart inheritance patterns, using the crossing of siblings, and backcrossing to parents to determine how inheritance functioned.