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.
Click here to return to the Molecular Biology Archives
Update: June 2012