Sex chromosomes: male versus female
In a man's somatic cells there is always an X and a Y chromosome and in awoman's somatic cells there are always two X chromosomes.
In women one of the two X chromosomes is deactivated at an early stage of embryonicdevelopment. Which one is deactivated seems to be chosen at random. Inany case it is not the same chromosome that is deactivated in everycell. Women therefore express some of the characteristics whose genesare situated on the X chromosome to varying degrees.
In a man the two sex chromosomes are not identical but we still consider them as a pair. There is little genetic information on the Y chromosome, but it plays a crucial role in the development of the embryo. The Y chromosome initiates production of male hormones and therefore the development of male sexual characteristics.