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Archiver > GENEALOGY-DNA > 2006-05 > 1147940231


From: "David Whyte" <>
Subject: RE: [DNA] New comparison of human and chimp DNA
Date: Thu, 18 May 2006 01:17:11 -0700
In-Reply-To: <2fd.56b6460.319d0fbf@aol.com>


I think, although I am no expert in the matter, that it has to do with male
sterility in hybrids. In two populations on their way to becoming different
species, there will be a progression from hybrids that are fertile and
healthy, to hybrids that are less fertile or even sterile, to hybrids that
are inviable. At some point, the two populations diverge enough that mating
becomes impossible (horse and giraffe) or unpalatable (the "yuk" factor).
Once some level of sterility arises in the hybrids the forces of speciation
have started. If there are sterile or inviable offspring after mating
between variant populations, they tend to be of the sex with different sex
chromosomes (males in humans, females in some other species, like
butterflies). This has become known as Haldane's Rule, after his
authoritative studies on the subject. Physically this could be due to the
inability of the X and Y chromosomes from the two populations to pair up,
resulting in aspermia, or it could be due to the genetic environment
changing, so that the X from one population is unable to function properly
in a cell with autosomal genes from the other population. Maybe it's a
combination of chromosomal and genic effects. Whatever the cause, it is the
males that are sterile because in the females there is a backup X to mask
these effects. It is interesting to note that although the X is overall
gene poor, it has lots of genes for sperm formation as well as cognitive
development. There's probably a joke in there...

-----Original Message-----
From: [mailto:]
Sent: Wednesday, May 17, 2006 3:46 PM
To:
Subject: Re: [DNA] New comparison of human and chimp DNA



In a message dated 5/17/2006 4:02:42 P.M. Pacific Standard Time,
writes:

"The genes that are a barrier to speciation tend to be on the
X-chromosome," said David Reich, the main author of the study.



Anyone care to expand on this statement?


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