Human sex chromosomes. Computer illustration of human X and Y chromosomes, and strands of DNA (deoxyribonucleic acid). There are 22 pairs of chromosomes and also the gender determining pair. In men, this comprises one X and one Y chromosome. In women, it is two X chromosomes. The Y chromosome carries genetic information responsible for the development of male characteristics. Chromosomes carry genetic information in the form of genes, lengths of DNA that act as recipes for production of proteins.