Some traits are inherited through sex chromosomes. An example of such a feature is the red-green colour perception defect or color blindness.

Color blindness is caused by a mutation that influences the individual's the X chromosome. X-linked color blindness is a recessive trait.

Males inherit their single X chromosome from their mothers. As a result, they can become color blind if their signle X chromosome has the color perception defect. In females, the colour perception defect manifests itself only when it is inherited from both parents. For this reason, red-green blindness is much more common in men than in women.

Image on the right: Can you see the number four in the image?