how is the sex of a zygote determined
Best Answer: There are no other factors. The sex of a zygote is determined by which sperm fertilizes the egg. On the last pair of chromosomes, women are XX, whereas men are XY. A woman can only donate X to the offspring, whereas a man can donate X or Y. Which one (X or Y) is donated by the man is what determines the sex of the zygote. Since the sperm contains half of the chromosomes of a regular cell, each sperm will contain either an X or a Y. So, it all depends on which sperm is the lucky one that fertiliaes the egg.