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Asked by sophiesweeneyx to Kate, Kieren, Nicola, Rowena, Roy on 13 Mar 2014.
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Rowena Fletcher-Wood answered on 13 Mar 2014:
Blue eyes are recessive, so get passed on as genes only when there isn’t another gene for brown eyes which is stronger. If you have blue eyes your parens have blue eyes. I have grey eyes rather than blue which comes from mixing blue and brown. My mother has brown eyes and my father blue.
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Nicola Rogers answered on 13 Mar 2014:
There are two factors that affect the colour of your eyes. Firstly, our iris scatters light, and blue light scatters more than red light, so they tend to look blue (in the same way that the sky looks blue). In addition to this, the amount of a pigment called melanin in the eye will affect the colour. Melanin varies from light brown to black in humans, as the amount of melanin increases, and if there is very little melanin this will contribute very little to the colour. So if you have hardly any melanin in the eyes then they will look blue from the scattering, whereas if there is a lot of melanin then they will look brown.
Interestingly babies are usually born with blue eyes usually because the melanin in the eyes doesn’t develop until they are a bit older – so they can either remain blue or turn brown as the baby develops!
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Kate Nicholson answered on 14 Mar 2014:
Because of the genes that you have that determine how much pigment will develop in the iris. The shade can shift a little depending on how the muscles in your eyes are behaving and the blood vessels. They all look black if you look at them in infra red – slightly creepy! This is just because of how they scatter and absorb the light.
Comments
sophiesweeneyx commented on :
Rowena, my mum has brown eyes and my dad has blue eyes and so does my sister so why aren’t my eyes grey like yours?
Kate commented on :
Sophie I have blue eyes too, and my mam had brown(ish) eyes and my dad has blue – so the brown gene didn’t win out in my family like it should either! I think that it is not just the one gene that determines what happens but also the amount of melanin pigment too – I don’t have a lot of that in my skin either!
Rowena commented on :
Ah, maybe your mum has a brown eye gene and a blue eye gene and she looks brown eyes but she passed you the blue eye gene? We have a gene from each parent so she could have a blue gene if one of her parents had blue eyes.
Rowena commented on :
*This different is called genotype (the two genes you have) whilst phenotype is what you look like. If you have a brown eye gene in your genotype you have a brown eye phenotype or a mixed colour like grey, but you don’t get blue eyes because brown eyes win or merge. You don’t have brown eyes in your genotype because you didn’t get grey eyes!