Colour blindness
Red-green colour blindness is not 'blindness' at all but just a difficulty in distinguishing shades between red and green. It affects about one in 12 men, but only one in 200 women. If you are a man with colour blindness, then you may have nephews or grandsons who also have this trait. Your children may all have normal vision, though all your daughters will be carriers of the trait. Female carriers may have sons with colour blindness, but not daughters.
