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{{short description|Transmission of genes occurring outside the nucleus}}
'''Extranuclear inheritance''' or '''cytoplasmic inheritance''' is the transmission of genes that occur outside the [[Cell nucleus|nucleus]]. It is found in most [[eukaryotes]] and is commonly known to occur in cytoplasmic [[organelles]] such as [[mitochondrion|mitochondria]] and [[chloroplast]]s or from cellular parasites like [[virus]]es or [[bacteria]].<ref name="Birky_94">{{cite journal |author=C. W. Birky, Jr. |year=1994 |title=Relaxed and stringent genomes: why cytoplasmic genes don't obey Mendel's laws |journal=[[Journal of Heredity]] |volume=85 |issue=5 |pages=355–366 |doi=10.1093/oxfordjournals.jhered.a111480 }}</ref><ref name="Jain_etal_07">{{cite journal |author1=Sangeeta Jain |author2=Nima Goharkhay |author3=George Saade |author4=Gary D. Hankins |author5=Garland D. Anderson |year=2007 |title=Hepatitis C in pregnancy |journal=[[American Journal of Perinatology]] |volume=24 |issue=4 |pages=251–256 |doi=10.1055/s-2007-970181|pmid=17447189 }}</ref><ref name="Duff_96">{{cite journal |author=Patrick Duff |year=1996 |title=HIV infection in women |journal=[[Primary Care Update for OB/GYNS]] |volume=3 |issue=2 |pages=45–49 |doi=10.1016/S1068-607X(95)00062-N}}</ref>

== Organelles ==
[[File:Mitochondrion structure.svg|thumb|upright=1.35|left|Mitochondria contain their own [[Mitochondrial DNA|DNA]]. They are passed on by mothers to their children via the cytoplasm of the egg.]]

Mitochondria are organelles which function to transform energy as a result of [[cellular respiration]]. Chloroplasts are organelles which function to produce sugars via [[photosynthesis]] in plants and algae. The [[genes]] located in [[mitochondria]] and chloroplasts are very important for proper cellular function. The [[mitochondrial DNA]] and other extranuclear types of DNA replicate independently of the DNA located in the nucleus, which is typically arranged in chromosomes that only replicate one time preceding cellular division. The extranuclear genomes of mitochondria and chloroplasts replicate independently of cell division, instead, they replicate in response to a cell's increased energy needs which vary throughout the cell's lifespan. Since they replicate independently, genomic recombination of these genomes is rarely found in offspring, contrary to nuclear genomes in which recombination is common.
[[File:Egg cell fertilization - Zygote.png|thumb|]]
Mitochondrial diseases are inherited from the mother, not from the father. Mitochondria with their mitochondrial DNA are present in the egg cell prior to fertilization by the sperm. In many cases of fertilization, the head of the sperm enters the egg cell, leaving its middle part, with its mitochondria, behind. The mitochondrial DNA of the sperm often remains outside the [[zygote]] and is excluded from inheritance.

== Parasites ==
Extranuclear transmission of viral genomes and symbiotic bacteria is also possible. An example of viral genome transmission is [[perinatal]] transmission. This occurs from mother to fetus during the perinatal period, which begins before birth and ends about 1 month after birth. During this time viral material may be passed from mother to child in the bloodstream or breastmilk. This is of particular concern with mothers carrying [[HIV]] or [[hepatitis C]] viruses.<ref name="Jain_etal_07"/><ref name="Duff_96"/> Symbiotic cytoplasmic bacteria are also inherited in organisms such as insects and protists.<ref name="Sapp_04">{{cite journal |author=Jan Sapp |year=2004 |title=The dynamics of symbiosis: an historical overview |journal=[[Canadian Journal of Botany]] |volume=82 |issue=8 |pages=1046–1056 |doi=10.1139/b04-055}}</ref>

== Types ==
Three general types of extranuclear inheritance exist.
*'''Vegetative segregation''' results from random replication and partitioning of cytoplasmic organelles. It occurs with chloroplasts and mitochondria during mitotic cell divisions and results in daughter cells that contain a random sample of the parent cell's organelles. An example of vegetative segregation is with mitochondria of asexually replicating yeast cells.<ref name="Birky_etal_78"/>
*'''Uniparental inheritance''' occurs in extranuclear genes when only one parent contributes organellar DNA to the offspring. A classic example of uniparental gene transmission is the [[maternal inheritance]] of human mitochondria. The mother's mitochondria are transmitted to the offspring at [[fertilization]] via the egg. The father's mitochondrial genes are not transmitted to the offspring via the sperm. Very rare cases which require further investigation have been reported of paternal mitochondrial inheritance in humans, in which the father's mitochondrial genome is found in offspring.<ref name="Schwartz_Vissing_03">{{cite journal |author1=Marianne Schwartz |author2=John Vissing |year=2003 |title=New patterns of inheritance in mitochondrial disease |journal=[[Biochemical and Biophysical Research Communications]] |volume=310 |issue=2 |pages=247–251 |doi=10.1016/j.bbrc.2003.09.037|pmid=14521902 }}</ref> Chloroplast genes can also inherit uniparentally during [[sexual reproduction]]. They are historically thought to inherit maternally, but paternal inheritance in many species is increasingly being identified. The mechanisms of uniparental inheritance from species to species differ greatly and are quite complicated. For instance, chloroplasts have been found to exhibit maternal, paternal and biparental modes even within the same species.<ref name="Birky_95">{{cite journal |author=C. W. Birky, Jr. |year=1995 |title=Uniparental inheritance of mitochondrial and chloroplast genes: mechanisms and evolution |journal=[[Proceedings of the National Academy of Sciences USA]] |volume=92 |issue=25 |pages=11331–11338 |doi=10.1073/pnas.92.25.11331 |pmid=8524780 |pmc=40394|bibcode=1995PNAS...9211331B |doi-access=free }}</ref><ref name="Hanse_etal_06">{{cite journal |author1=A. Katie Hansen |author2=Linda K. Escobar |author3=Lawrence E. Gilbert |author-link3=Lawrence E. Gilbert |author4=Robert K. Jansen |year=2007 |title=Paternal, maternal, and biparental inheritance of the chloroplast genome in ''Passiflora'' (Passifloraceae): implications for phylogenic studies |journal= American Journal of Botany|volume=94 |pages=42–46 |issue=1 |doi=10.3732/ajb.94.1.42 |pmid=21642206}}</ref> In tobacco (''Nicotiana tabacum''), the mode of chloroplast inheritance is affected by the temperature and the enzymatic activity of an exonuclease during male gametogenesis.<ref>{{cite journal |last1=Chung |first1=Kin Pan |last2=Gonzalez-Duran |first2=Enrique |last3=Ruf |first3=Stephanie |last4=Endries |first4=Pierre |last5=Bock |first5=Ralph |title=Control of plastid inheritance by environmental and genetic factors |journal=Nature Plants |date=16 January 2023 |volume=9 |issue=1 |pages=68–80 |doi=10.1038/s41477-022-01323-7 |pmid=36646831 |pmc=9873568 |language=en |issn=2055-0278}}</ref>
*'''Biparental inheritance''' occurs in extranuclear genes when both parents contribute organellar DNA to the offspring. It may be less common than uniparental extranuclear inheritance, and usually occurs in a permissible species only a fraction of the time. An example of biparental mitochondrial inheritance is in the [[yeast]] ''[[Saccharomyces cerevisiae]]''. When two [[haploid]] cells of opposite mating type fuse they can both contribute mitochondria to the resulting [[diploid]] offspring.<ref name="Birky_94"/><ref name="Birky_etal_78">{{cite journal |author1=C. William Birky, Jr. |author2=Robert L. Strausberg |author3=Jean L. Forster |author4=Philip S. Perlman |s2cid=24730742 |year=1978 |title=Vegetative segregation of mitochondria in yeast: estimating parameters using a random model |journal=[[Molecular and General Genetics]] |volume=158 |issue=3 |pages=251–261 |doi=10.1007/BF00267196}}</ref>

==Mutant mitochondria==

''Poky'' is a mutant of the fungus ''[[Neurospora crassa]]'' that has extranuclear inheritance. ''Poky'' is characterized by slow growth, a defect in [[mitochondrial ribosome]] assembly and deficiencies in several [[cytochrome]]s.<ref name="pmid4275176">{{cite journal |vauthors=Lambowitz AM, Bonner WD |title=The mitochondrial beta-cytochromes of the wild type and poky strains of Neurospora crassa. Evidence for a component reduced only by dithionite |journal=J. Biol. Chem. |volume=249 |issue=9 |pages=2886–90 |date=May 1974 |doi=10.1016/S0021-9258(19)42713-0 |pmid=4275176 |doi-access=free }}</ref> Studies of ''poky'' mutants were among the first to establish an extranuclear mitochondrial basis for inheritance of a particular genotype. It was initially found, using genetic crosses, that ''poky'' is maternally inherited.<ref name="pmid16589122">{{cite journal |vauthors=Mitchell MB, Mitchell HK |title=A Case of "Maternal" Inheritance in Neurospora Crassa |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=38 |issue=5 |pages=442–9 |date=May 1952 |pmid=16589122 |pmc=1063583 |doi= 10.1073/pnas.38.5.442|bibcode=1952PNAS...38..442M |doi-access=free }}</ref> Subsequently, the primary defect in the ''poky'' mutants was determined to be a [[deletion (genetics)|deletion]] in the [[mitochondrion|mitochondrial]] DNA sequence encoding the small subunit of mitochondrial [[ribosomal RNA]].<ref name="pmid6233613">{{cite journal |vauthors=Akins RA, Lambowitz AM |title=The [poky] mutant of Neurospora contains a 4-base-pair deletion at the 5' end of the mitochondrial small rRNA |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=81 |issue=12 |pages=3791–5 |date=June 1984 |pmid=6233613 |pmc=345306 |doi= 10.1073/pnas.81.12.3791|bibcode=1984PNAS...81.3791A |doi-access=free }}</ref>

==See also==
* [[Maternal effect]]
* [[Plasmid]]
* [[Xenia (plants)]]

== References ==
{{reflist|32em}}

==External links==
* https://web.archive.org/web/20080521093531/http://www.tamu.edu/classes/magill/gene603/Lecture%20outlines/cytoplasmic%20inh/CYTOPLASMIC_INHERITANCE.html

[[Category:Genetics]]

Extranuclear inheritance - История изменений

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