content: It's interesting because in women the body has to deal with two X chromosomes, both of which want to dictate the phenotype, so one of the chromosomes gets silenced rather than 'sharing' control like many of our other chromosomes. Oftentimes (less so in humans) that genetic silencing is localized, so you will be phenotypically different in two different parts of the same tissue.  Men and women have two copies of every chromosome, except the X and Y, where females have two X and no Y, and males have one X and one Y.