Sex Determination

The human body has 23 pairs of chromosomes in its nucleus. 22 of these pairs control our characteristics, Which are called autosomes. The 23rd chromosome pair determines sex.

  • In females, the sex chromosomes are the same – XX
  • In males, the sex chromosomes are different – XY

50% of the offspring’s alleles are donated from each parent. The female always contributes an X chromosome, whereas the male has a 50/50 chance of contributing either an X or a Y chromosome.

So, half of all sperm cells will carry an X chromosome and the other half will carry a Y chromosome, whereas all egg cells will carry an X chromosome.

This means that a child’s biological sex is determined by the chromosome that the father contributes.

Genetic Diagrams

We can see the inheritance of sex using a Punnett Square diagram:

There is a 50% chance that the offspring will be a girl (XX) and a 50% chance that the offspring will be a boy (XY). So, the ratio of female to male offspring is 1:1. So on average, 50% of the offspring will be female and 50% will be male.