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What is 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.Enlarge
Ishihara tests are used to detect colour blindness.
How is colour blindness inherited?
Your eyes detect colour with special cells that contain chemical pigments. People with red-green colour blindness have pigment genes that are missing, or not working properly. Genes on the X-chromosome normally make these chemical pigments. As females have two X-chromosomes, they usually have at least one set of working pigment genes. But males have only one X-chromosome (and a Y-chromosome, which does not have any pigment genes), so if they have a single altered pigment gene they will be colour blind.
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The inheritance of colour blindness.
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