genetics

[Alison Murie]

On Apr 29, 2010, at 8:58 PM, victor steinbok wrote:

> ---------------------- Information from the mail header
> -----------------------
> Sender:       American Dialect Society <ADS-L at LISTSERV.UGA.EDU>
> Poster:       victor steinbok <aardvark66 at GMAIL.COM>
> Subject:      Re: genetics
> -------------------------------------------------------------------------------
>
> 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
>>
~~~~~~~~~~
I defer to your greater learning.  I realized too late that what I
said (above) 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!
The hair of this female, once excessively thick, is thinning fast, but
approaching eighty with low thyroid function, it would be tricky to
sort out the genetic factor.
AM

------------------------------------------------------------
The American Dialect Society - http://www.americandialect.org