What is Sex chromosomes?

Of the 23 pairs of human chromosomes, 22 are alike in the two sexes; the 23rd pair is made of the sex chromosomes: two X chromosomes in a female (XX), one X and one Y in a male (XY). The Y is small, carries few genes, and is transmitted only from father to son; every egg carries an X, and a sperm carries either an X or a Y, so the father’s sperm decides the chromosomal sex of the child, with equal chances.