Sex chromosome

Sex chromosome: The X chromosome or the Y chromosome, in humans. The sex chromosomes determine the sex of an individual. As a general rule, normal females have two X chromosomes while normal males have an X and a Y chromosome. The sex chromosomes evolved from an ancient pair of autosomal chromosomes. The X is considerably larger and richer in genes than the Y. The X contains 153 M bp (mega base pairs) and 1095 genes while the Y contains 50 M bp and 148 genes. The sex chromosomes, by convention, are the 23rd and last pair of chromosomes in a normal human karyotype.