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Name: Dion
Status: Other
Grade:  Other
Location: N/A
Country: United States
Date: May 2005

How is gender selected at conception? Is it random or are there reasons -- i.e. acidity levels temperature at conception? Does the sperm have a precursor to give off the X or Y chromosome?

The sex of a child is determine at coneption by whether a sperm carrying a Y chromosome or a sperm carrying an X chromosome fertilizes the egg. If the fertilizing sperm carries an Y chromosome, the embryo develops into a male. In humans, 51.4% of the time the egg is fertilized by a Y carrying sperm (the sex ratio at birth is 106 males for every 100 females. The reason why the sex ratio is not exactly 50% is not known but possible theories are that Y sperm swim faster because the Y chromosome is much smaller than the X chromosome or that the Y sperm live longer than the X chromosome bearing sperm for some reason.

Ron Baker, Ph.D.

Well, probability wise, it is supposed to be random. Half the sperm have a Y and half have an X. But some research shows that the biochemistry of the female reproductive system may be more receptive to Y or X sperm.


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