Male sex chromosomes. Fluorescence in situ hybridisation (FISH) micrograph of the X and Y chromosomes of a human male. Every human cell has 46 chromosomes, of which 22 pairs are identical in both males and females. However, in males the last pair is composed of an X (left) and a much smaller Y chromosome (right), while females have two X chromosomes. Here, the chromosomes have been tagged to show the ends of their long arms (in green). The magenta areas have been stained with DAPI. Chromosomes carry genetic information in the form of genes and the sex chromosomes carry the genes that control sexual development.