A man has XY chromosomes. A woman has XX chromosomes The sex of a baby is determined by the father, as he provides either an X chromosome (resulting in a girl) or a Y chromosome (resulting in a boy) through his sperm. The mother always contributes an X chromosome through her egg, making the combination either XX for a girl or XY for a boy. The Y chromosome of Jesus was provided supernaturally by the Holy Spirit during the Incarnation, as Mary could only provide an X chromosome. This miraculous i