Kosambi centimorgans

deustachio at mcclb0.med.nyu.edu deustachio at mcclb0.med.nyu.edu
Tue Nov 3 18:33:14 EST 1992


Nigel Walker asked:
> What is a Kosambi centimorgan?  How does it differ from a plain vanilla
> centimorgan?  Is there a difference? 
and Joe Felsenstein replied:
>
> I think a Kosambi centimorgan is just a name for an ordinary centimorgan,
> when that centimorgan is estimated from recombination fractions, using
> the mapping function of Kosambi:
>
>    Kosambi, D. D.  1944. The estimation of map distance from recombination
>    values.  Annals of Eugenics  12: 172-175.
>
> There are other mapping functions, and there is no real reason to append the
> name of the mapping function to the name "centimorgan" as if what it
> calculates is incommensurable with ordinary centimorgans.
>
It's not quite that simple.  Mapping functions embody theories about inter-
ference (interactions - positive or negative - among a given number of
progeny chromosomes into a 'true' (contingent on the validity of your theory)
map distance.  Different mapping functions make quite different assumptions
in this respect and, especially for low density maps (i.e., recombination
fractions greater than 10% between adjacent markers), yield appreciably
different results.  At the same time, all the mapping functions I know of
converge as the distance between adjacent markers gets small. 

Peter D'Eustachio
NYU Medical Center - Biochemistry
peter at mcbcm2.med.nyu.edu



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