The chromosomes that determine the sex of an organism are called sex chromosomes. The 23rd chromosome in the human body is the sex chromosome. The two sex chromosomes are X and Y. It is called heterosome. A chromosome that does not play any role in determining the sex of an organism is called an autosome. Human body has 22 pairs of autosomes. Autosomes are identical XX. External differences are seen in male and female animals. This is called sexual dimorphism.