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Archiver > GENEALOGY-DNA > 2006-04 > 1144281650


From: "Diana Gale Matthiesen" <>
Subject: RE: [DNA] X inactivation [hemophilia]
Date: Wed, 5 Apr 2006 20:00:50 -0400
In-Reply-To: <23d.a037952.3165a477@aol.com>


My recollection from undergraduate genetics (eons ago) is that a homozygous
female will have hemophilia, but that the reason, at least historically (before
effective drugs were available), they're not well known is that 1) homozygosity
is extremely rare and 2) they don't survive the onset of mensus. Does my memory
serve me?

Diana

> -----Original Message-----
> From: [mailto:]
> Sent: Wednesday, April 05, 2006 5:54 PM
> To:
> Subject: Re: [DNA] X inactivation [hemophilia]
>
> In a message dated 04/05/06 3:14:19 PM Pacific Daylight Time,
> writes:
>
> > If only one of a woman's two X chromosomes is expressed at
> random, then
> > why do women never get hemophilia? As I understand it, the
> hemophilia gene
> > resides on one of the X chromosomes in a woman and if it
> is present, it will
> > be suppressed by the corresponding gene on the other X.
> Since men have only
> > one X chromosome, if they have the gene, they get the disease.
>
> In this case, it's not so much a matter of "suppression" as
> the fact that the
> normal gene in active chromosomes can express enough of the
> clotting factor
> to prevent everyday problems. If you actually measure the
> amount of clotting
> factor, it will be about 50% of normal (the 50-50 chance of
> whether the X with
> the normal version or the X with the mutation is
> inactivated), but that's still
> enough to do the job most of the time. Since X inactivation
> is random,
> though, some heterozygous females may end up with less than
> 50% of the normal amount
> and experience prolonged bleeding times.
>
> Ann Turner
>
>
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