Smallness of the human Y chromosome

Laurence Martin Cook LCOOK at fs1.scg.man.ac.uk
Wed Nov 1 12:44:17 EST 2000

In mosquitoes (Aedes) there are M-linked (= Y-linked) meiotic drive 
genes and suppressor genes on the m (or X) chromosome.  Numerous 
evolutionary events seem to have taken place, so that inter-
population crosses produce sex ratio distortion while intra-
population crosses do not, or do so to a much lesser extent.  The Mm 
chromosomes are equally large and carry many other loci. 


> Andrew Gyles  <syzygium at alphalink.com.au> wrote:
> >Under natural selection a human population in which the males had
> >the 'anti-X gamete' Y chromosome would suffer the disadvantages of a
> >surplus of males and a scarcity of females. In the long run natural
> >selection would favour subsequent mutants of the 'anti-X gamete' Y
> >chromosome in which those mutant genes that discriminated against the
> >production of X-bearing gametes in spermatogenesis or sperm maturation
> >were deleted or rendered inactive.
> This is the step in the argument that I doubt.  A Y chromosome
> with meiotic drive *always* has a local advantage over one without,
> even when the population as a whole is suffering badly from
> excessive males.  Group selection might possibly be able to
> push down the frequency of driven Y, but even if one accepts that
> group selection is a realistic possibility here, it tends to be
> weak and slow compared to individual selection.
> On the other hand, the X and the autosomes see a straightforward
> advantage in not allowing the Y they're with to push them into 
> a male zygote when males are wildly overrepresented, so X and
> autosomal suppressors are straightfowardly advantageous.  It
> seems to me, therefore, that the usual way a driven Y stops being
> driven is that a non-Y suppressor becomes fixed, not that the
> drive locus is damaged or deleted.
> There are a fair number of observations of meiotic drive in the
> literature; you could look for references to suppressors/revertants 
> and see what chromosome they're on.  I'd predict they're usually
> not on the Y.
> Mary Kuhner mkkuhner at genetics.washington.edu
> ---
> Laurence M. Cook
The Manchester Museum 
University of Manchester
Manchester M13 9PL U.K.
and:_lcook2 at excite.com


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