In human body, there are 23 pairs of chromosomes in the cell. Out of these, 22 pairs have a maternal and a paternal copy of genes, but do not take part in sex-determination in human being. The 23rd pair, which is not always a perfect pair, is called sex chromosomes.
Women have a perfect pair of sex chromosomes XX. But men have a mismatched pair of chromosomes in the form XY. This cell is divided meiotically in both men and women to form gametes. All children will inherit an X chromosome from their mother regardless of whether they are boys or girls and an X or Y chromosomes from their father. Thus, the sex of the children will be determined by what they inherit from their father. A child who inherits an X chromosome from her father will be a girl, and one who inherits a Y chromosome from him will be a boy.