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Are people with blue eyes really mutants of brown eyed people?

I heard in the Telegraph that people with blue eyes are mutants of brown eyed people. I was wondering why scientists think this and what lead them to this conclusion?
Julia Greater London (age 5-14)

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2 Responses

  1. Hello Julia,
    Blue eye colour is caused by a mutation(change ) in an eye colour gene.
    Eye colour genes have the code for a coloured chemical or pigment found in the iris of your eyes. Everyone inherits two copies of every gene – one from each of their parents.
    If you inherit a blue eye colour gene from each parent you will have blue eyes. This is because the blue eye colour gene does not produce any coloured chemical. If you inherit one blue eye gene and one brown eye gene( technically called alleles), you will have brown eyes.
    If you inherit two copies of the brown eyed gene you will also have brown eyes.

  2. Dear Julia,

    Marion’s response is an accurate description of the genetics of eye colour but I am not sure if it addresses your question directly. A brown eye is the result of the action of an enzyme, tyrosinase, (another vesion of the enzyme is also responsible for brown hair pigment) during the development of the eye. So people with blue eyes do not have the eye tyrosinase and as such are derived from ancestors who lost a functioning tyrosinase encoding gene, presumably by mutation. As Marion states you have to have two copies of the non-functioning gene to get blue eyes.

    In fact most babies are born with blue eyes and it takes a while for the tyrosinase enzyme to produce the brown pigment, melanin.

    Blue eye colour is not the default colour of the eye. Albinos have pink eyes, with the red colour originating from the blood vessels in the eye. White mice are albino mice and as you see they have pink eyes.

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