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From:
Subject: Re: [DNA] Are X results reported differently by 23andMe anddeCODEme?
Date: Tue, 19 Jan 2010 21:34:21 EST


The Mb to cM ratio is experimentally determined and varies over different
regions of the chromosomes, so you can't really calculate it. If you use
deCODEme's genome browser to determine the boundaries of the segment in
megabases, you can read the approximate values off a graph in this file:


http://web.archive.org/web/20070113005025/http://compgen.rutgers.edu/maps/compare.pdf

Chances are that your segments are in a "flat" section of the graph, where
the cM count doesn't increase very much as you add physical bases.

You can also download a set of tables and look up the cumulative cM count
at different physical base positions from this set of files:


http://hapmap.ncbi.nlm.nih.gov/downloads/recombination/2006-10_rel21_phaseI+II/rates/

Ann Turner





In a message dated 1/19/2010 3:08:05 PM Pacific Standard Time,
writes:

> In deCODEme my aunt shares 2 fragments on her X which are between a 5Mb
> and 10Mbs with another woman. In 23andMe she does not show any matching
> segments on her X with that same person.
>
> Are those fragment sizes on their X large enough to confirm a shared
> ancestor who likely lived in the last 400 years? What is the cut off point for
> 23andMe? How do you calculate the conversion from Mb to cM?



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