During spermatogenesis, two types of gametes are produced of which 50 percent carry the X- chromosome and the rest 50 percent has Y-chromosome besides the autosomes.
Females produce only one type of ovum with an X- chromosome. In case the ovum fertilises with a sperm carrying X chromosome the zygote develops into a female (XX) and with Y-chromosome results into a male off spring. Thus the genetic makeup of the sperm that determines the sex of the child
