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[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]