Re: What makes a male/female ratio equal ??

From: Dan Christensen (dchris_at_allstream.net)
Date: 08/13/04 

Date: Fri, 13 Aug 2004 15:50:43 -0400

"George Greene" <greeneg@greeneg-cs.cs.unc.edu> wrote in message
news:xesisbmzvmn.fsf@greeneg-cs.cs.unc.edu...
> mtx014@linux.services.coventry.ac.uk (Robert Low) writes:
>
> : Dan Christensen <dchris@allstream.net> wrote:
> : >In humans, as with most animals (not all), gender is entirely
determined the
> : >individual's chromosomes which are inherited from his/her parents. See
any
> : >introductory biology text for details. Briefly, you have two sex
> : >chromosomes -- one from your father and one from your mother. There
are two
> : >types of sex chromosome, X and Y. Females have 2 X chromosomes -- one
from
> : >their mother and one from their father. That's what makes them female.
Males
> : >have one X chromosome from their mother, and a Y chromosome from their
> : >father. That's why the numbers roughly balance in humans.
>
> The numbers DON'T roughly balance in humans.
> There are more births of boys. By a percentage
> far enough away from 50/50 that it is NOT a rough
> balance. It is like 53-47.
>
> : Well, that together with the fact that males produce
> : X sperm and Y sperm in roughly equal proportions.
>

Yes. I forgot to mention that.

> Yes, we do. And that equality is not even rough;
> it is VERY close to exact. But XX and XY sperm have
> differently-shaped heads and the spermatozoon that fertilizes
> the egg is basically the one that GETS THERE FIRST, so an
> an aerodynamic advantage in swimming MATTERS.

It may be more complicated than that. I read (I'm no expert) that X sperms
are slower, but can swim farther. A newly released egg is thus more likely
to encounter X sperms -- the Y sperms having previously exhausted themselves
in a "sprint."

Dan

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