female:male ratio in K-3 kids

Shawn Snaples CSM0352 at acs.tamu.edu
Fri Jan 12 15:42:19 EST 1996

klynn at STUDENTS.WISC.EDU (Karyn Lynn) wrote:
>Yeah, but the optimum pH for survival is different for x sperm and y sperm.
>Maybe other factors that change as women age are also influential.
>>Sophie Wilson (sophiewi at uoguelph.ca) wrote:
>>: And I dimly remember from a biology class that as women
>>: age, they are more likely to produce female babies than male babies.  Is
>>: it possible that the average age of the MOTHERS might be a factor here?

Yes, there are statistically more male sperm that meet of up eggs; I think the ratio is about 1 X sperm : 1.5 Y sperm.  But the male fetuses tend to have more problems.  The birth ratio is 1 female : 1.05 males.  And then due to all sorts of biological reasons, at about 20 years old,  the ratio is approximately 1:1.  Older then that, there are statistically more females than males.

The theory is that since females have 2 X chromosomes, they compensate for any gene on the X chromosome that is non-functional.  Males with a defective gene on the X chromosome tend to die young.  Hence, the reasoning goes, there are more males to start with, so that everything is equal at prime reproductive age.  Actually, this is true for any hemizygous sex; in humans it's the male.

Second, there are all sorts of theories on what is more likely to produce a male or a female child.  The one I find most interesting is that the female sperm seem to be more hardy.  So if you want a baby girl, you have sex several hours after ovulation.  Or several hours before ovulation for a boy.

Of course, it's all "statistical."  And things that have a 1 in a million chance happen 9 times out 10.  :)

Shawn Snaples
Genetics student

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