50.3%% of the world’s population is male. How can this be explained genetically? Since the male sperm provides the X or Y for female and male respectively, is there a greater number of Y sperm than X sperm? Or does it have a selective advantage in the battle for the egg cell?
Answer
A sperm cell that will give rise to a son contains (as you yourself already mentioned) a Y chromosome, a sperm cell that gives rise to a daughter contains an X chromosome. Now a Y chromosome is no more than an X with a bit less (men have only 1 set of genetic information for a number of characteristics). A ‘male sperm cell’ is therefore somewhat lighter and also somewhat faster than a ‘female’; which makes it more likely that such a ‘male sperm cell’ will win the race to the egg cell. The chance is not much higher, but it is still there and ensures that the male/female ratio is not 50/50, but slightly tilted in favor of the men.
Answered by
dr. Jelle Boeve-de Pauw
Biology, Education, Environmental Education
Prinsstraat 13 2000 Antwerp
http://www.uantwerpen.be
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