Some conditions have been traced to genes that usually occur only in the Y chromosome, and hence can be transmitted only by fathers to their sons. These include bark-like skin (ichthyosis hystrix gravior), dense hairy growth on the ears (hypertrichosis), nonpainful hard lesions of the hands and feet (keratoma dissipatum), and a form of webbing of the toes (fusion of the skin between the 2nd and 3rd toes). (Montague, Ashley. The Natural Superiority of Women. NY: Collier Books, 1952, 1974, pp 80-81)