Chromosome 15 – Eye colour


[MUSIC PLAYING] I’m in London to talk
about the eye. It’s one of the most
impressive feats of engineering that you’re
likely to see. But I’m not talking about
the London Eye. I’m talking about
the human eye. [MUSIC PLAYING] Now we know that the eye is an
incredible mechanical marvel. But when you stare into
someone’s eyes, you’re not thinking about engineering. The first thing that you usually
notice is the colour, and the colour of the eyes is
down in part to a gene on Chromosome 15. Now that gene is known as
OCA2 or, to you or me, oculocutaneous albinism II. Now in order to work out how the
colour in the eye works, let’s have a closer look. [MUSIC PLAYING] The coloured part of the
eye is the iris. And in the iris, the OCA2 gene
gives instructions for the production of a pigment
called melanin. Now when lots of melanin is
produced, the result is dark brown eyes. [MUSIC PLAYING] When little or no melanin is
produced, we get blue eyes. [MUSIC PLAYING] Now the blue doesn’t come from a
coloured structure or a blue pigment, but arises from light
being scattered through the iris in a similar way to how
light scatters through the earth’s atmosphere and
gives us a blue sky. [MUSIC PLAYING] Although we don’t yet fully
understand the genetics of it, it’s the same kind of cells
and the same production of melanin that causes our skin
to darken a few days after we’ve been in the sun. Although in the middle of winter
in England, I think that’s unlikely to happen
anytime soon. [MUSIC PLAYING]

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