(Off Topic) genetics and baldness

[Joel S. Berson]

At 4/29/2010 05:41 PM, Garson O'Toole wrote:
>Researchers have long been aware of a genetic variant on the X
>chromosome that was linked to male pattern baldness, Richards said.
>   "That's where the idea that baldness is inherited from the mother's
>side of the family comes from," he explained. "However it's been long
>recognized that that there must be several genes causing male pattern
>baldness. Until now, no one could identify those other genes. If you
>have both the risk variants we discovered on chromosome 20 and the
>unrelated known variant on the X chromosome, your risk of becoming
>bald increases sevenfold."

And Alison Murie wrote today:
>I realized too late that what I said (above [but excised]) is
>absurd, even in terms of the simplistic recessive/
>dominant paradigm, since, if the male parent had a recessive
>baldness gene, he could pass that on to offspring as easily as the
>female, which would upset the female-only inheritance scheme!

First,(in my long-ago message), I reversed the X and Y chromosomes!

Second, Garson's description is more like it.  In my naive ignorance
I didn't think a single X-linked gene from a mother (which is all a
male gets; his other is a Y) could cause baldness in a son, whether
the gene were dominant or recessive.  But if the presence of another
gene, on another chromosome (20 in the above), is required, then
certain combinations of the two could cause male pattern baldness,
and the absence of the X-linked variant would mean no pattern
baldness in the male

By the way, Wikipedia says male pattern baldness (that is, androgenic
alopecia) can occur in female humans also.  That, too, fits -- a
woman could have the X-linked gene and the necessary variant on
chromosome 20, of which she (just like the man) has two (chromosomes, that is).

Joel

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