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Humans slow mutation rate (Science)

Daniel Weinreich dmw at MCZ.HARVARD.EDU
Thu Apr 27 08:19:08 EST 1995


On 24 Apr 1995, Grier Page wrote:

>This question is being addressed in a series of papers form Dr. W-H Li's lab. 

I again confess my former ignorance of these studies!  In response to my
original post I received (and forwarded to this list) a note from W.-H. Li
which gave some of these recent references (Nature 362:745, PNAS 91:827,
JME 40:70). 

> [The putatively faster Y-clock] is not the result of what enzymatic
> differences but due to difference in the number of divisions a egg goes
> through verses a sperm.

Putting aside the extremely difficult question of whether the level of
purifying selection acting on homologous X- and Y-linked introns is
identical, I'm still intrigued by an alternate explanation offered to the
list by Ingrid Jakobsen (ingrid at helios.anu.edu.au), who wrote: 

> DNA in sperm is methylated, while in ova it is not.  This would mean
> that genes on the Y chromosome would experience more C to T transitions
> independently of any effect that may be caused by cell division.

There are indeed some C->T transitions from ZFY to ZFX (e.g. see Fig 1c of
the Nature paper).  If one controls for this effect (e.g. by discarding
such transitions, or at least down-weighting them) does the whole
phenomenon of "male-drive" go away?  I doubt it; but has anyone run the
numbers? 

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