Male sex chromosomes. Colored Scanning Electron Micrograph (SEM) of the X and Y chromosomes in a human male, known as the sex chromosomes. Every human cell has 46 chromosomes of which 22 pairs are identical in females and males. The last pair is composed of two X chromosomes in a female, whereas a male has one X (at top) and one Y chromosome (at bottom). Chromosomes carry genetic information in the form of genes. Sex chromosomes determine gender of male or female. In a female, only one X chromosome is active. In a male, the X chromosome is active and the shorter arm of the male Y chromosome (lower left) has genes for male genital development. Magnification: unknown.