genetics

[victor steinbok]

Uhm... actually, no. I was very specific in my description. If the
gene is recessive, it would not show up in women when matched with a
normal pair. If it were dominant, it would absolutely show up in
women. I don't see how it could be any other way. It shows up in men
because there is no matched pair. This is true about ANY genetically
linked disorder that travels on X--the responsible gene is either
defective (a nonce gene, believe it or not) or recessive, never
dominant.

Either way, it makes absolutely no sense for baldness. Baldness is
extremely common--it is one of the most common characteristics. The
issue is more early baldness, but even there the distribution very
strongly favors men over women--very few women go bald early in life
and they do not develop MPB--or it would not be called Male Pattern.
With such a common distribution, the probability of ending up with two
baldness-inducing Xs would be very high and would result in early
baldness common among women. However, it is not. This actually
suggests that the Y chromosome, in this particular case, does make a
contribution. An alternative hypothesis would tie baldness to the
ratio of male-specific to female-specific hormones--this actually
makes more sense, as many women do lose their hair with age, although
this is rarely described as baldness because it does not follow MPB.
So, even though there is a possibility of sex link, a hormonal trigger
is more likely (these are not mutually exclusive, of course).

Whatever it is, one thing absolutely cannot be the cause--a simple,
single dominant gene. Sorry, I just can't accept that description.

VS-)

On Thu, Apr 29, 2010 at 6:09 PM, Alison Murie <sagehen7470 at att.net> wrote:
>
> On Apr 29, 2010, at 5:42 PM, victor steinbok wrote:
>
>>
>> Actually, the way you describe it, it would have to be recessive,
>> e.g., hemophilia. The idea is that because women have a pair of X
>> chromosomes, one would carry the dominant gene that blocks the
>> disorder--more precisely, in such cases, this gene is functioning
>> normally in producing a particular set of proteins--while the damaged
>> gene does not produce the proteins. Then, if the damaged gene is
>> inherited by male offspring, there is no corresponding normal gene in
>> the Y chromosome to offset the damage caused by the defective one from
>> the lone X. This is why sometimes women DO end up expressing syndromes
>> usually associated with men (colorblindness, hemophilia, baldness).
>>
>> To be honest, I've seen a lot of conflicting information concerning
>> heredity of baldness, so I am not even sure if this claim carries any
>> weight. But it still makes a good (peripheral) story.
>>
>> VS-)
>>
>> On Thu, Apr 29, 2010 at 4:54 PM, Alison Murie <sagehen7470 at att.net>
>> wrote:
>>
>>> It would have to be carried on the X, or a woman wouldn't have it.
>>> Presumably it is dominant, or there would need to be two, one from
>>> each parent.  The mechanism may be more complicated, controlled by
>>> more than one pair of genes.  I'm no geneticist, just parroting stuff
>>> I read somewhere,  confirmed by my biologist husband.
>>> AM
>>
> ~~~~~~~~~~~~
> Um, you are right, in that it could be recessive, but it wouldn't have
> to be.   The offspring could get a recessive from each parent ( the
> male having inherited one that was not expressed) & would then express
> the baldness.  On the other hand, if it were dominant, it wouldn't
> matter what the male contributed.
> Of course it isn't really this simple.  The contribution of
> environment is incalculable, for one thing.
> AM
>

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