The Y chromosome is an allosome (sex chromosome) possessed by only male animals, which also possess one X chromosome in contrast to females, which possess two X chromosomes. It was fittingly discovered in 1905 by a woman (Nettie Stevens).
The Y chromosome does not participate in recombination, and so the Y chromosome is inherited without changes from one generation to another, meaning that all the males in a family will have the same Y chromosome as their ancestors. At the same time, the Y chromosome is the fastest evolving human chromosome, although it appears to hold very few genes (which generally form a cocktail for "maleness" and are non-vital).
