Chromosome
There are 46 chromosomes in a human as 23 pairs. Everyone has a set of chromosomes from their father and a set from their mother. They include a pair of sex chromosomes. The mother's eggs always contain an X chromosome, while the father's sperm contains either a Y chromosome or an X chromosome. That determines the sex of the child. If the child gets a Y chromosome from the father it is male. If it gets an X from the father, it is female.