Male sex chromosomes. Computer artwork of an X and Y symbolising the male sex chromosomes. An individual's sex is determined by the presence or absence of the Y chromosome. Women have two X chromosomes, while men have an X and a Y. Chromosomes consist of very condensed deoxyribonucleic acid (DNA). DNA contains sections, called genes, which encode the body's genetic information. The Y chromosome only contains genes for 'maleness', for example a gene that triggers the development of the testes, and is much smaller than the X chromosome.