Smallness of the human Y chromosome

Mary K.Kuhner mkkuhner at kingman.genetics.washington.edu
Wed Nov 1 10:17:58 EST 2000

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


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