Ik Lata, Color Blindness

The royal family had hemophelia, and e were able to trace it back with a family tree. It's because they're the on the x chromosome that is responsible for certain types of color blindness. There's also this really cool concept of x inactivation mosaicism where females do have two x somes,. But in each individual cell of her body, she's only manifesting one of those ex chromosomes.