Sex chromosome

Sex chromosomes are chromosomes which determine the sex of individual organisms. In men, for example, there are 23 pairs of chromosomes, and one of these pairs are sex chromosomes. Females have two X chromosomes, males have one X and one Y. An egg always carries a single X, while sperms carry either an X or a Y. That is how sex is determined in humans.Bainbridge, David A. 2003. The X in sex: how the X chromosome controls our lives. Harvard. 

Not all organisms have their sex determined by chromosomes. Those that do use the sex chromosome system have variations in how it happens. The account above is generally true for mammals.Vallender J. & Lahn T. 2006. Multiple independent origins of sex chromosomes in amniotes. Proceedings of the National Academy of Sciences of the United States of America 103 (48): 18031–18032.

 Related pages 
Sex determination 
Karyotype
Chromosome

 References 

Category:Biological reproduction
Category:Chromosomes