Men determine the sex of a baby depending on whether their sperm is carrying an X or Y chromosome. An X chromosome combines with the mother’s X chromosome to make a baby girl (XX) and a Y chromosome will combine with the mother’s to make a boy (XY).
If a baby has chromosome Y in the sex chromosome set. Like XY than that is a baby boy. If the sex chromosome set has XX sequence than that is a baby girl. So, the Y chromosome determines the sex of the baby.
