Santimorgan

Santimorgan (abbreviated: cM ) in genetics is the unit of measurement of genetic distances between polymorphic fragments of the genome ( loci or markers ), which is defined as the distance at which the probability of recombination of genes in meiosis is 1%.

Content

Etymology

The name was given by Alfred Henry Stoutevant in honor of his teacher: Thomas Hunt Morgan ^[1] .

Relationship to physical distance

The number of base pairs that the centimorgan corresponds to varies widely across the entire genome — different regions of the chromosome have a different tendency to cross .

One centimorgan corresponds to approximately one million base pairs of the human body ^[2] ^[3] .

Plasmodium falciparum has an average recombination distance of ~ 15 kb per centimorgan: markers divided by 15 kb of DNA (15 thousand nucleotides ) have an expected level of 1% cross-generation per generation.

Please note that non- synth genes (genes located on different chromosomes) are inherently separated and the distances in the CM to them are not applicable.

Relation to recombination probability

Since genetic recombination between the two markers is detected only if there is an odd number of crosses between them, the distance, expressed in centimoragans, does not quite correlate with the probability of genetic recombination.

Assuming the Haldane mapping function, where the number of crosses is related to the Poisson distribution ^[4] , genetic distance d will result in an odd number of crosses, and therefore will detect genetic recombination, with a probability calculated using the formula:

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

{\ displaystyle \ 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}}\,,

{\ displaystyle {} = \ 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 function of the hyperbolic sine . The probability of recombination is about d / 100 for small values of d and reaches 50% as d tends to infinity.

Notes

↑ Santimorgan
↑ NIH ORDR - Glossary - C
↑ Harvey Lodish, Arnold Berk, Paul Matsudaira, Chris A. Kaiser, Monty Krieger, Matthew P. Scott, Lawrence Zipursky, and James Darnell. Molecular Cell Biology, Fifth Edition. - San Francisco: WH Freeman, 2004. - P. 396. - "" ... in humans centered on an average represents a distance of about 7.5x10E5 base pairs "". - ISBN 0-7167-4366-3 .
↑ Department of Plant Sciences (Undec.) .

Literature

Su X; Ferdig, MT; Huang, Y; Huynh, CQ; Liu, A; You, J; Wootton, JC; Wellems, TE, Plasmodium falciparum parasite (English) // Science: journal. - 1999. - November ( vol. 286 , no. 5443 ). - P. 1351-1353 . - DOI : 10.1126 / science.286.5443.1351 . - PMID 10558988 .

[humbio-1] Santimorgan

[2] NIH ORDR - Glossary - C

[3] Harvey Lodish, Arnold Berk, Paul Matsudaira, Chris A. Kaiser, Monty Krieger, Matthew P. Scott, Lawrence Zipursky, and James Darnell. Molecular Cell Biology, Fifth Edition. - San Francisco: WH Freeman, 2004. - P. 396. - "" ... in humans centered on an average represents a distance of about 7.5x10E5 base pairs "". - ISBN 0-7167-4366-3 .

[4] Department of Plant Sciences (Undec.) .