genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar wor ...

, paternal mtDNA transmission and paternal mtDNA inheritance refer to the incidence of

mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...

(mtDNA) being passed from a

father A father is the male parent of a child. Besides the paternal bonds of a father to his children, the father may have a parental, legal, and social relationship with the child that carries with it certain rights and obligations. An adoptive fathe ...

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 (also known as Mendelism) is a type of biological inheritance following the principles originally proposed by Gregor Mendel in 1865 and 1866, re-discovered in 1900 by Hugo de Vries and Carl Correns, and later popularize ...

. In contrast, mtDNA transmission from both parents occurs regularly in certain bivalves.

In animals

Paternal mtDNA inheritance in animals varies. For example, in

Mytilidae Mytilidae are a family of small to large marine and brackish-water bivalve molluscs in the order Mytilida. One of the genera, '' Limnoperna'', even inhabits freshwater environments. The order has only this one family which contains some 52 gener ...

mussels, paternal mtDNA "is transmitted through the sperm and establishes itself only in the male gonad." In testing 172

sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus ''Ovis'', in everyday usage it almost always refers to domesticated s ...

, "The Mitochondrial DNA from three lambs in two half-sib families were found to show paternal inheritance." An instance of paternal leakage resulted in a study on chickens. There has been evidences that paternal leakage is an integral part of mitochondrial inheritance of ''

Drosophila simulans ''Drosophila simulans'' is a species of fly closely related to ''D. melanogaster'', belonging to the same ''melanogaster'' species subgroup. Its closest relatives are ''D. mauritiana'' and ''D. sechellia''. Taxonomy This species was discovere ...

''.

In humans

human mitochondrial genetics Human mitochondrial genetics is the study of the genetics of human mitochondrial DNA (the DNA contained in human mitochondria). The human mitochondrial genome is the entirety of hereditary information contained in human mitochondria. Mitochondri ...

, there is debate over whether or not paternal mtDNA transmission is possible. Many studies hold that paternal mtDNA is never transmitted to offspring. This thought is central to mtDNA

genealogical DNA test A genealogical DNA test is a DNA-based test used in genetic genealogy that looks at specific locations of a person's genome in order to find or verify ancestral genealogical relationships, or (with lower reliability) to estimate the ethnic mixt ...

ing and to the theory of

mitochondrial Eve In human genetics, the Mitochondrial Eve (also ''mt-Eve, mt-MRCA'') is the matrilineal most recent common ancestor (MRCA) of all living humans. In other words, she is defined as the most recent woman from whom all living humans descend in an ...

. 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 Patrilineality, also known as the male line, the spear side or agnatic kinship, is a common kinship system in which an individual's family membership derives from and is recorded through their father's lineage. It generally involves the inheritanc ...

lineage. In

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

, paternal mitochondria found in the

sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...

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 is a small (8.6 kDa) regulatory protein found in most tissues of eukaryotic organisms, i.e., it is found ''ubiquitously''. It was discovered in 1975 by Gideon Goldstein and further characterized throughout the late 1970s and 1980s. Fo ...

to select them for later destruction inside the

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

. Some

in vitro fertilization In vitro fertilisation (IVF) is a process of fertilisation where an egg is combined with sperm in vitro ("in glass"). The process involves monitoring and stimulating an individual's ovulatory process, removing an ovum or ova (egg or eggs) f ...

(IVF) techniques, particularly intracytoplasmic sperm injection (ICSI) of a sperm into an

oocyte An oocyte (, ), oöcyte, or ovocyte 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 a female fetus in the ovary during female gametogenesis. The female ...

, may interfere with this. It is now understood that the tail of the

, which contains additional mtDNA, may also enter the

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...

. 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..."). A few studies indicate that, very rarely, a small portion 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,'' which was peer-reviewed and printed in ''Proceedings of the National Academy of Sciences.'' According to the study's abstract: The mixing of maternal and paternal mtDNA was thought to have been found in chimpanzees in 1999 and in humans in 1999 and 2018. This last finding is significant, as biparental mtDNA was observed in subsequent generations in three different families leading to the conclusion that, although the maternal transmission dogma remains strong, there is evidence that paternal transmission does exist and there is a probably a mechanism which, if elucidated, can be a new tool in the reproductive field (e.g. avoiding mitochondrial replacement therapy, and just using this mechanism so that the offspring inherit the paternal mitochondria). However, there has been only a single documented case among humans in which as much as 90% of a single tissue type's mitochondria was inherited through paternal transmission. According to the 2005 study ''More evidence for non-maternal inheritance of mitochondrial DNA?'',

heteroplasmy Heteroplasmy is the presence of more than one type of organellar genome (mitochondrial DNA or plastid DNA) within a cell or individual. It is an important factor in considering the severity of mitochondrial diseases. Because most eukaryotic cells c ...

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. However, the 2005 study states: A study published in PNAS in 2018 titled ''Biparental Inheritance of Mitochondrial DNA in Humans'' has found paternal mtDNA in 17 individuals from three unrelated multigeneration families with a high level of mtDNA heteroplasmy (ranging from 24 to 76%) in a total of 17 individuals.

In protozoa

Some organisms, such as ''

Cryptosporidium ''Cryptosporidium'', sometimes informally called crypto, is a genus of apicomplexan parasitic alveolates that can cause a respiratory and gastrointestinal illness (cryptosporidiosis) that primarily involves watery diarrhea (intestinal cryptosp ...

'', 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 bananas. Some Conifers also show paternal inheritance of mitochondria, such as the coast redwood, ''

Sequoia sempervirens ''Sequoia sempervirens'' ()''Sunset Western Garden Book,'' 1995:606–607 is the sole living species of the genus '' Sequoia'' in the cypress family Cupressaceae (formerly treated in Taxodiaceae). Common names include coast redwood, coastal ...

''.

References

External links

* * * * *
as PDF

Paternal inheritance of mitochondrial DNA
(PDF) by Marianne Schwartz and John Vissing, 2002 *
PubMed

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