If you ever need examples for X-linked characteristics, they are found in tortoiseshell (orange & black) housecats. The gene for orange coat colour and the gene for black coat colour both travel on the X chromosome. This is why almost all black and orange housecats are female (XX - one X gene carries the orange gene, the other carries the black gene). It is possible to have a male tortoiseshell cat, but his genes would be XXY, instead of the normal XY that most male mammals have. Also, this doesn't apply to other species of cats like tigers.