The sex of a baby is determined by two sex chromosomes inherited from both the genetic parents. A baby will normally inherit one sex chromosome from the mother and one from the father. A woman has two X chromosomes and thus gives either of her X chromosomes. The father has one X chromosome and one Y chromosome, can give either his X or Y chromosome. The egg (from the mother) already contains an X chromosome. Therefore the sex of a baby is determined by the X or Y chromosome of the sperm cell from the father. A baby girl will result if there is XX, and a baby boy will result if the final arrangement is XY. It is possible to have an abnormal arrangement of sex chromosomes, however, this is very rare.