In human, 23 pairs (46) chromosomes are present out of these 22 pairs have a maternal and a paternal copy. These chromosomes (autosomes) determine the characters other than sex. The 23rd pair of chromosomes called sex chromosomes. Women have perfect pair of sex chromosomes, both called XX chromosomes. Men have a mismatched pair of chromosomes—one is a normal size X chromosome and a short one called Y chromosome. So, women have XX chromosomes and men have XY sex chromosomes.
All children will inherit an X chromosome from their mother regardless of whether they are boys or girls. It means that the sex of the children will be determined by what sex chromosome they inherit from their father. A child who inherits an X chromosome from father will be girl, and one who inherits a Y chromosome from father will be a boy.

Fig. Birth of a girl or boy baby