Explanation: All human beings have 23 pairs of chromosomes- 22 pairs of autosomes and 1 pair of sex chromosomes. Females possess XX pairs of sex chromosomes while males have XY. During fertilisation, the male nucleus possesses either X or Y chromosome which combines with the X chromosome of the female. As a result, a zygote is formed with either XX or XY chromosomes and the autosomes. Hence, the equal genetic contribution of male and female parents is ensured in the progeny.