The X chromosome codes quite a few crucial proteins [0], such as certain clotting factors (that's why women rarely get haemophilia), or retinal proteins (that's

The X chromosome codes quite a few crucial proteins [0], such as certain clotting factors (that's why women rarely get haemophilia), or retinal proteins (that's why women see more colors, and rarely get daltonism). It is pretty impossible for a fetus to develop with a YY genotype. [0] http://ghr.nlm.nih.gov/chromosome/X/show/Genes http://ghr.nlm.nih.gov/chromosome/X/show/Genes