In cats, tortoiseshell coat color appears in females. A tortoiseshell coat has patches of dark brown fur and patches of orange fur that each in total cover about half the body but have a unique pattern in each female. Male cats can be either dark brown or orange, but a male cat with tortoiseshell coat is rarely produced. Two sample crosses between males and females from pure-breeding lines produced the tortoiseshell females shown.

Cross I          P: dark brown male × orange female
                      F₁: orange males and tortoiseshell females
Cross II         P: orange male × dark brown female
                      F₁: dark brown males and tortoiseshell females

Why are tortoiseshell cats female?