Answer: The father determines the biological sex of a baby
Explanation: Human beings have two sex chromosomes, males have XY chromosomes whereas females have XX chromosomes. During fertilization, an egg from a woman fuses with a sperm cell from a man to form a zygote. Women have two X chromosomes (XX) and any point in time they can only release an egg bearing an X chromosome but males have one X and one Y chromosome, therefore they can either release a sperm cell with an X chromosome or a sperm cell with a Y chromosome. When an egg with X-chromosome fuses with a sperm cell with an X chromosome, the resulting baby is a female but when an egg with an X chromosome fuses with a sperm cell with a Y chromosome, the resulting baby is a male.
What makes the difference in both sexes is the Y chromosome from the man, therefore the father determines the biological sex of a baby.
