• Question: Why are people's pupil different colours?

    Asked by to Edward, Ian, Mathew, Naomi, sakshisharda on 17 Jun 2014. This question was also asked by .
    • Photo: Ian Stephenson

      Ian Stephenson answered on 17 Jun 2014:

      Eye colour is down to a chemical called melanin. If your body is good at making it, then you have brown eyes, if its bad at it then you have blue.

      Your body gets its ability to make melanin genetically, and its typically taught that you have two genes, and get one from each parent. If either can make melanin then you have brown eyes, even if you have a recessive non-melanin making (blue eyed) gene from the other parent.

      However while there is some truth in that, its more complex… For a start what about green eyes? Its not simply the case that you can either make melanin or not – people make different amounts, and while there is a genetically inherited component, there’s a lot of other factors too.

    • Photo: Naomi Osborne

      Naomi Osborne answered on 18 Jun 2014:

      Eye colour is controlled by two or more genes inherited from your parents. How these genes interact to make eye colour is still unknown. Babies are all born with blue eyes – if they have genes able to produce melanin, their eyes turn brown at around 1 year old.

      Some people can have two different coloured eyes (although this is rare) – my chemistry teacher had one blue and one brown one. This is thought to be down to varied expression of these genes (and maybe others which we still don’t know about) in the cells of each eye.

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