The sex of a zygote is determined by sex chromosomes in humans.
In human beings, females have two X chromosomes and males have one X and one Y chromosome. Therefore, females are XX and males are XY. The gametes, as we know, receive half of the chromosomes. The male gametes have 22 autosomes and either the X or the Y sex chromosome. The mother provides only X chromosomes. Thus, the sex of a zygote is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.