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Archiver > GENEALOGY-DNA > 2004-05 > 1083578832


From:
Subject: Re: [DNA] Y-chromosome map [number of genes]
Date: Mon, 3 May 2004 06:07:12 EDT


In a message dated 05/01/04 8:55:08 PM Pacific Daylight Time,
writes:

> By the way, unless the non-MSY genes are inactive, I'm not sure I agree
> that
> they should be omitted from the total number of genes on the Y-chromosome.
> From a genealogical standpoint, these genes are still inherited directly
> from father-to-son, generation after generation.

Actually, the non-MSY regions (the pseudo-autosomal regions at the tips of
the Y) have a VERY high rate of recombination with the X chromosome, so genes
and genetic markers in those regions can come from your father's mother as well
as your father's father. I hadn't really thought about it explicitly until I
came across a section in a textbook at PubMed, but recombination on the X/Y
pair must occur within a very limited region, compared to all the other
chromosomes which can recombine anywhere along their lengths. That pushes the
recombination percentage up for the small pseudo-autosomal region of the Y:

http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=hmg.section.1708

Nancy Custer's biology tutorial has an animation of recombination (also
called crossing over):

http://www.contexo.info/DNA_Basics/Meiosis.htm

You also asked about the vast unmapped portion of the Y. It may never be
fully sequenced (or at least the priority is very low). The textbook above also
has a section about this region, composed of "heterochromatin." It has highly
repetitive sequences with no landmarks to anchor things. The length of the
repeat patterns may be a few thousand bases, so it's hard to pin down the order of
things.

Ann Turner - GENEALOGY-DNA List Administrator
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