Paternal mtDNA transmission
Encyclopedia
In genetics, paternal mtDNA transmission and paternal mtDNA inheritance refer to the incidence of mitochondrial DNA
(mtDNA) being passed from a father
to his offspring. Paternal mtDNA inheritance is observed in a small proportion of species; in general, mtDNA is passed unchanged from a mother to her offspring, making it an example of non-Mendelian inheritance
. In contrast, mtDNA transmission from both parents occurs regularly in certain bivalves.
mussels, paternal mtDNA "is transmitted through the sperm and establishes itself only in the male gonad." In testing 172 sheep
, "The Mitochondrial DNA from three lambs in two half-sib families were found to show paternal inheritance."
In human mitochondrial genetics
, there is debate over whether or not paternal mtDNA transmission is possible. Many studies hold that paternal mtDNA is never transmitted to offspring. This belief is central to mtDNA genealogical DNA test
ing and to the theory of mitochondrial Eve
. The fact that mitochondrial DNA is maternally inherited enables researchers to trace maternal lineage
far back in time. (Y chromosomal DNA
, paternally inherited, is used in an analogous way to trace the agnate lineage.)
In sexual reproduction
, paternal mitochondria found in the sperm
are actively decomposed, thus preventing "paternal leakage". Mitochondria in mammalian sperm are usually destroyed by the egg cell after fertilization. In 1999 it was reported that paternal sperm mitochondria (containing mtDNA) are marked with ubiquitin
to select them for later destruction inside the embryo
. Some in vitro fertilization (IVF) techniques, particularly intracytoplasmic sperm injection (ICSI) of a sperm into an oocyte
, may interfere with this.
It is now understood that the tail of the sperm
, which contains additional mtDNA, may also enter the egg
. This had led to increased controversy about the fate of paternal mtDNA.
Some sources state that so little paternal mtDNA is transmitted as to be negligible ("At most, one presumes it must be less than 1 in 1000, since there are 100 000 mitochondria in the human egg and only 100 in the sperm (Satoh and Kuroiwa, 1991).") or that paternal mtDNA is so rarely transmitted as to be negligible ("Nevertheless, studies have established that paternal mtDNA is so rarely transmitted to offspring that mtDNA analyses remain valid..."). One study stated that about 1–2% of a person's mitochondria can be inherited from the father."
The controversy about human paternal leakage was summed up in the 1996 study Misconceptions about mitochondria and mammalian fertilization: Implications for theories on human evolution. The following quotation comes from the abstract to that peer-reviewed study printed in the Proceedings of the National Academy of Sciences:
The mixing of maternal and paternal mtDNA was thought to have been found in humans and chimpanzees in 1999. However, there has been only a single documented case of human paternal mitochondrial DNA transmission, and it was linked to infertility.
According to the 2005 study More evidence for non-maternal inheritance of mitochondrial DNA?, heteroplasmy
is a "newly discovered form of inheritance for mtDNA. Heteroplasmy introduces slight statistical uncertainty in normal inheritance patterns." Heteroplasmy may result from a mutation during development which is propagated to only a subset of the adult cells, or may occur when two slightly different mitochondrial sequences are inherited from the mother as a result of several hundred mitochondria being present in the ovum.
, have mitochondria with no DNA whatsoever.
s. Some Conifers also show paternal inheritance of mitochondria, such as the coast redwood, Sequoia sempervirens.
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
(mtDNA) being passed from a father
Father
A father, Pop, Dad, or Papa, is defined as a male parent of any type of offspring. The adjective "paternal" refers to father, parallel to "maternal" for mother...
to his offspring. Paternal mtDNA inheritance is observed in a small proportion of species; in general, mtDNA is passed unchanged from a mother to her offspring, making it an example of non-Mendelian inheritance
Mendelian inheritance
Mendelian inheritance is a scientific description of how hereditary characteristics are passed from parent organisms to their offspring; it underlies much of genetics...
. In contrast, mtDNA transmission from both parents occurs regularly in certain bivalves.
In animals
Paternal mtDNA inheritance in animals varies. For example, in MytilidaeMytilidae
Mytilidae is a family of small to large saltwater mussels, marine bivalve mollusks in the order Mytiloida. It is the only family in the order...
mussels, paternal mtDNA "is transmitted through the sperm and establishes itself only in the male gonad." In testing 172 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...
, "The Mitochondrial DNA from three lambs in two half-sib families were found to show paternal inheritance."
In humans
Human mitochondrial genetics
Human mitochondrial genetics is the study of the genetics of the DNA contained in human mitochondria. Mitochondria are small structures in cells that generate energy for the cell to use, and are hence referred to as the "powerhouses" of the cell....
, there is debate over whether or not paternal mtDNA transmission is possible. Many studies hold that paternal mtDNA is never transmitted to offspring. This belief is central to mtDNA genealogical DNA test
Genealogical DNA test
A genealogical DNA test examines the nucleotides at specific locations on a person's DNA for genetic genealogy purposes. The test results are not meant to have any informative medical value and do not determine specific genetic diseases or disorders ; they are intended only to give genealogical...
ing and to the theory of mitochondrial Eve
Mitochondrial Eve
In the field of human genetics, Mitochondrial Eve refers to the matrilineal "MRCA" . In other words, she was the woman from whom all living humans today descend, on their mother's side, and through the mothers of those mothers and so on, back until all lines converge on one person...
. The fact that mitochondrial DNA is maternally inherited enables researchers to trace maternal lineage
Matrilineality
Matrilineality is a system in which descent is traced through the mother and maternal ancestors. Matrilineality is also a societal system in which one belongs to one's matriline or mother's lineage, which can involve the inheritance of property and/or titles.A matriline is a line of descent from a...
far back in time. (Y chromosomal DNA
Y chromosome
The Y chromosome is one of the two sex-determining chromosomes in most mammals, including humans. In mammals, it contains the gene SRY, which triggers testis development if present. The human Y chromosome is composed of about 60 million base pairs...
, paternally inherited, is used in an analogous way to trace the agnate lineage.)
In 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...
, paternal mitochondria found in the sperm
Spermatozoon
A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote...
are actively decomposed, thus preventing "paternal leakage". Mitochondria in mammalian sperm are usually destroyed by the egg cell after fertilization. In 1999 it was reported that paternal sperm mitochondria (containing mtDNA) are marked with ubiquitin
Ubiquitin
Ubiquitin is a small regulatory protein that has been found in almost all tissues of eukaryotic organisms. Among other functions, it directs protein recycling.Ubiquitin can be attached to proteins and label them for destruction...
to select them for later destruction inside the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
. Some in vitro fertilization (IVF) techniques, particularly intracytoplasmic sperm injection (ICSI) of a sperm into an oocyte
Oocyte
An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell which undergoes a mitotic...
, may interfere with this.
It is now understood that the tail of the sperm
Spermatozoon
A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote...
, which contains additional mtDNA, may also enter the egg
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
. This had led to increased controversy about the fate of paternal mtDNA.
Some sources state that so little paternal mtDNA is transmitted as to be negligible ("At most, one presumes it must be less than 1 in 1000, since there are 100 000 mitochondria in the human egg and only 100 in the sperm (Satoh and Kuroiwa, 1991).") or that paternal mtDNA is so rarely transmitted as to be negligible ("Nevertheless, studies have established that paternal mtDNA is so rarely transmitted to offspring that mtDNA analyses remain valid..."). One study stated that about 1–2% of a person's mitochondria can be inherited from the father."
The controversy about human paternal leakage was summed up in the 1996 study Misconceptions about mitochondria and mammalian fertilization: Implications for theories on human evolution. The following quotation comes from the abstract to that peer-reviewed study printed in the Proceedings of the National Academy of Sciences:
The mixing of maternal and paternal mtDNA was thought to have been found in humans and chimpanzees in 1999. However, there has been only a single documented case of human paternal mitochondrial DNA transmission, and it was linked to infertility.
According to the 2005 study More evidence for non-maternal inheritance of mitochondrial DNA?, heteroplasmy
Heteroplasmy
Heteroplasmy is the presence of a mixture of more than one type of an organellar genome within a cell or individual...
is a "newly discovered form of inheritance for mtDNA. Heteroplasmy introduces slight statistical uncertainty in normal inheritance patterns." Heteroplasmy may result from a mutation during development which is propagated to only a subset of the adult cells, or may occur when two slightly different mitochondrial sequences are inherited from the mother as a result of several hundred mitochondria being present in the ovum.
In protozoa
Some organisms, such as CryptosporidiumCryptosporidium
Cryptosporidium is a protozoan that can cause gastro-intestinal illness with diarrhea in humans.Cryptosporidium is the organism most commonly isolated in HIV positive patients presenting with diarrhea...
, have mitochondria with no DNA whatsoever.
In plants
In plants, it has also been reported that mitochondria can occasionally be inherited from the father, e.g. in bananaBanana
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. Some Conifers also show paternal inheritance of mitochondria, such as the coast redwood, Sequoia sempervirens.
See also
- Y-chromosomal AdamY-chromosomal AdamIn human genetics, Y-chromosomal Adam is the theoretical most recent common ancestor from whom all living people are descended patrilineally . Many studies report that Y-chromosomal Adam lived as early as around 142,000 years ago and possibly as recently as 60,000 years ago...
- PatrilinealityPatrilinealityPatrilineality is a system in which one belongs to one's father's lineage. It generally involves the inheritance of property, names or titles through the male line as well....
- MatrilinealityMatrilinealityMatrilineality is a system in which descent is traced through the mother and maternal ancestors. Matrilineality is also a societal system in which one belongs to one's matriline or mother's lineage, which can involve the inheritance of property and/or titles.A matriline is a line of descent from a...
- Human mitochondrial geneticsHuman mitochondrial geneticsHuman mitochondrial genetics is the study of the genetics of the DNA contained in human mitochondria. Mitochondria are small structures in cells that generate energy for the cell to use, and are hence referred to as the "powerhouses" of the cell....
- Human migrationHuman migrationHuman migration is physical movement by humans from one area to another, sometimes over long distances or in large groups. Historically this movement was nomadic, often causing significant conflict with the indigenous population and their displacement or cultural assimilation. Only a few nomadic...
- RecLOHRecLOHRecLOH is a term in genetics that is an abbreviation for "Recombinational Loss of Heterozygosity".This is a type of mutation which occurs with DNA by recombination. From a pair of equivalent , but slightly different genes, a pair of identical genes results...
- List of genetic genealogy topics
External links
(as PDF)- Paternal inheritance of mitochondrial DNA (PDF) by Marianne Schwartz and John Vissing, 2002
- PubMed: