• Question: How are people colour-blind?

    Asked by roflatop to Amy, Drew, Julia, Kimberley, Sara on 20 Jun 2011.
    • Photo: Amy MacQueen

      Amy MacQueen answered on 19 Jun 2011:

      Good question roflatop!

      The average human retina (in the eye) contains two kinds of light cells: the rod cells (active in low light) and the cone cells (active in normal daylight). Normally, there are three kinds of cones which have sensitivities to different wavelengths of light (they are sometimes called blue cones, red cones and green cones). Normal colour vision depends on the way these cones detect light!
      Colour blindness can be caused by accidents and damage to the eye but mostly is genetic (to do with the DNA you inherit from your mum and dad). Many of the genes involved in colour vision are on the X chromosome. Girls have two of these and boys only have one – so its more common in boys as if they have one broken gene that makes them colour blind they don’t have a normal one to “override” it and restore normal vision as it were.

      For more details on the different gene defects that make us colour blind check out Wikipedia! 🙂

    • Photo: Sara Imari Walker

      Sara Imari Walker answered on 20 Jun 2011:

      Hey! Amy’s got this one nailed! One more thing to add – different kinds of color blindness depend on what is damaged (or missing due to genetic defect) in the eye. If cones are malfunctioning a person may be unable to distinguish colors at all, and will see in shades of gray (the cones enable us to distinguish details such as colors nicely). If you are missing a particular kind of rod, you may be missing out on just that color. So there are actually lots of kinds of colorblindness. Amy’s suggestion of wikipedia is a great reference! You should check it out =)

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