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Asked by myersh to Daniela, Hannah, Ian, Jono, Mark on 24 Jun 2013. This question was also asked by rebeccasedgwick, jayisbeast, eliciamcnally.
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Hannah Brotherton answered on 24 Jun 2013:
Hi myersh,
The colour of our iris is caused by melanin, which is a molecule we have in a skin that lets us tan in the sun. But we only tan brown…..not green, hazel, blue and brown like the colour of our eyes. We have all these different colours in our eyes because the way light scatters through a layer in our iris.Our genes determine the colour, but brown is a stronger gene than blue, So if dad has brown eyes and mum blue, the child will always have brown. However, sometimes, these genes can mutate (or just mix around) and this is why we have so many different colours like green or even grey (yes I know someone with grey eyes)
Animals have so many other colours, and this is because they have other molecules as well as melanin in their eyes like purines. This interact differently with light and make different colours.
But look at this – a photographer was able to take pictures really really really close of humans and animals eyes. It AMAZING. the link is:
😀
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Daniela Plana answered on 24 Jun 2013:
Hi myersh!
Our irises have a high content of pigments (colour molecules), which protect our eye… letting light go only into the pupil. As Hannah says, we only actually have melanin, that can make the coulour go from light brown to black… the the other colours are more complicated and have to do with how light interacts with different parts of the iris.
What colour our eyes are is determined, like many things in our body, by our DNA… some colours are dominant, like brown, and that’s why they are more common. Blue, on the other hand, is recessive and so you have to have oeioke with blue eyes both on your mom’s and your dad’s side of the family in order to get them.
Hope that helps!
Daniela -
Mark Hodson answered on 24 Jun 2013:
Hi myersh,
can’t really add anything to Daniela and Hannah’s answers. I always find it interesting that different eye colours are the most common in different countries. My wife is celtic, has red hair and blue eyes and when we visited China people stared at her and took photographs!
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Ian Wilson answered on 24 Jun 2013:
Hi myersh,
Your eyes contain a pigment (coloured material) called melanin. Different people have different concentrations of melanin in their eyes. But, despite what we see, the melanin only actually colours the iris brown or black. Very low concentrations of melanin give us light brown eyes and very high concentrations give us black eyes. The other colour irises that some people have (hazel, green and blue) are caused by light being scattered and bent (or ‘refracted’) when it hits the iris.
This is the exact same reason for the colour of the sky. Space is black yet, if you look up, you see blue. This is because light from the sun is being scattered when it hits gases and particles in the atmosphere. It’s kind of like when you shine a white light into a prism and the light comes out in a rainbow. The light from the sun is being refracted so it looks blue. The scattering of light like this is called ‘Rayleigh scattering’, after the scientist who discovered it.
As Hannah says, there’s also a genetic reason for the different iris colours we see. Scientists think there may be up to 16 genes that, between them, code for the melanin concentrations and the way that the eye bends light. There are set of 6 common mutations in these genes that cause the eye colours we see.
One final thing: most babies are born with blue eyes as there is little melanin in their irises. Different eye colours develop over time as melanin concentrations increase as the child grows up!
Hope that helps,
Ian
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