centimorgan

センチモルガン

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2017/08/18 02:07:09」(JST)

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In genetics, a centimorgan (abbreviated cM) or map unit (m.u.) is a unit for measuring genetic linkage. It is defined as the distance between chromosome positions (also termed loci or markers) for which the expected average number of intervening chromosomal crossovers in a single generation is 0.01. It is often used to infer distance along a chromosome. However, It is not a true physical distance.

Relation to physical distance

The number of base-pairs to which it corresponds varies widely across the genome (different regions of a chromosome have different propensities towards crossover) and it also depends on if the meiosis where the crossing-over takes place is a part of oogenesis (formation of female gametes) or spermatogenesis (formation of male gametes).

One centimorgan corresponds to about 1 million base pairs in humans on average. The relationship is only rough as the physical chromosomal distance corresponding to one centimorgan varies from place to place in the genome, and also varies between men and women since recombination during gamete formation in females is significantly more frequent than in males. Morton et al. calculated that the female genome is 4782 centimorgans long, while the male genome is only 2809 centimorgans long. Plasmodium falciparum has an average recombination distance of ~15 kb per centimorgan: markers separated by 15 kb of DNA (15,000 nucleotides) have an expected rate of chromosomal crossovers of 0.01 per generation. Note that non-syntenic genes (genes residing on different chromosomes) are inherently unlinked, and cM distances have no meaning between them.

Relation to the probability of recombination

Because genetic recombination between two markers is detected only if there are an odd number of chromosomal crossovers between the two markers, the distance in centimorgans does not correspond exactly to the probability of genetic recombination. Assuming Haldane's map function, where the number of chromosomal crossovers is according to a Poisson distribution, a genetic distance of d centimorgans will lead to an odd number of chromosomal crossovers, and hence a detectable genetic recombination, with probability

$\Pr[{\text{recombination}}|{\text{linkage of }}d{\text{ cM}}]=\sum _{k=0}^{\infty }\Pr[2k+1{\text{ crossovers}}|{\text{linkage of }}d{\text{ cM}}]$

${}=\sum _{k=0}^{\infty }e^{-d/100}{\frac {(d/100)^{2\,k+1}}{(2\,k+1)!}}=e^{-d/100}\sinh(d/100)={\frac {1-e^{-2d/100}}{2}}\,,$

where sinh is the hyperbolic sine function. The probability of recombination is approximately d/100 for small values of d and approaches 50% as d goes to infinity.

The formula can be inverted, giving the distance in centimorgans as a function of the recombination probability:

$d=50\ln \left({\frac {1}{1-2\Pr[{\text{recombination}}]}}\right)\,.$

Etymology

The centimorgan was named in honor of geneticist Thomas Hunt Morgan by his student Alfred Henry Sturtevant. Note that the parent unit of the centimorgan, the Morgan, is rarely used today.

References

Further reading

• Su X; Ferdig, MT; Huang, Y; Huynh, CQ; Liu, A; You, J; Wootton, JC; Wellems, TE (November 1999). "A genetic map and recombination parameters of the human malaria parasite Plasmodium falciparum". Science. 286 (5443): 1351–3. PMID 10558988. doi:10.1126/science.286.5443.1351. 

See also

• Mutation rate

English Journal

• Genome-wide recombination rate variation in a recombination map of cotton.

• Shen C1, Li X1,2, Zhang R1, Lin Z1.
• PloS one.PLoS One.2017 Nov 27;12(11):e0188682. doi: 10.1371/journal.pone.0188682. eCollection 2017.
• PMID 29176878

• Mapping stripe rust resistance gene YrZH22 in Chinese wheat cultivar Zhoumai 22 by bulked segregant RNA-Seq (BSR-Seq) and comparative genomics analyses.

• Wang Y1, Xie J2, Zhang H1, Guo B1, Ning S3, Chen Y2, Lu P2, Wu Q2, Li M1, Zhang D1, Guo G1, Zhang Y1, Liu D3, Zou S4, Tang J4, Zhao H5, Wang X5, Li J6, Yang W6, Cao T7, Yin G8, Liu Z9.
• TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik.Theor Appl Genet.2017 Oct;130(10):2191-2201. doi: 10.1007/s00122-017-2950-0. Epub 2017 Jul 15.
• PMID 28711956

• Mapping novel aphid resistance QTL from wild soybean, Glycine soja 85-32.

• Zhang S1, Zhang Z1, Bales C1, Gu C1, DiFonzo C2, Li M3, Song Q4, Cregan P4, Yang Z5, Wang D6.
• TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik.Theor Appl Genet.2017 Sep;130(9):1941-1952. doi: 10.1007/s00122-017-2935-z. Epub 2017 Jul 14.
• PMID 28710504

Japanese Journal

• Homozygosity Mapping on Homozygosity Haplotype Analysis to Detect Recessive Disease-Causing Genes from a Small Number of Unrelated, Outbred Patients

• PLoS ONE 6(9), e25059, 2011
• NAID 120005300511

• Genetic verification of induced gynogenesis and microsatellite–centromere mapping in the barfin flounder, Verasper moseri

• Aquaculture 272(1), S115-S124, 2007
• NAID 120001041004

• Abetalipoproteinemia caused by maternal isodisomy of chromosome 4q containing an intron 9 splice acceptor mutation in the microsomal triglyceride transfer protein gene.

• Arteriosclerosis, thrombosis, and vascular biology 19(8), 1950-1955, 1999-08
• NAID 120000807440

Related Links

• Centimorgan | Define Centimorgan at Dictionary.com

(genetics) a unit of chromosome length, used in genetic mapping, equal to the length of chromosome over which crossing over occurs with 1 per cent frequency ... centimorgan cen·ti·mor·gan (sěn'tə-môr'gən) n. Abbr. cM A unit of ...

• centimorgan - definition of centimorgan by Medical dictionary

Definition of centimorgan in the Medical Dictionary. centimorgan explanation. Information about centimorgan in Free online English dictionary. What is centimorgan? Meaning of centimorgan medical term. What does centimorgan ...

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