Eli5 : Why do some genes (like skin color) mix and shade upon inheritance while some don’t (like eye color) ?
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It has to do with how the tissue reflects light. Skin reflects light differently from the iris. That’s why there are blue and green eye colors but not blue and green skin colors. There are multiple kinds of melanin. Brown and black eumelanin cause darker skin tones, the different shades of brown eyes and brown, blonde and black hair. Pheomelanin produces red and yellow colors and tones lighter skin tones pink or yellowish. It also causes red/orange hair colors. Skin tone is determined by how many genes you have telling your body to produce melanin, so if you have a dark skinned parent you inherit more melanin genes. If you have a light skinned parent you inherit fewer melanin genes. That’s why skin tone looks like it mixes.
With eye color, there was a mutation around 10k years ago where suddenly people had eyes with little to no eumelanin. With limited eumelanin, you get light reflecting off of both the iris shape and pheomelanin and that affects whether someone has hazel, blue, green, or gray eyes. There’s actually a huge variation in eye colors, they’re potentially as unique as fingerprints, but it’s because the iris can reflect a range in colors and skin cannot. But because light eyes are the result of a single recessive mutation that’s why you can get a random blue-eyed child from two dark-eyed parents. There are around 60 genes affecting eye color and they get turned off and on so to speak, (it’s more whether you have a recessive or dominant allele) producing potentially unpredictable eye colors in children. Skin color is affected by the quantity of genes inherited instead of single gene mutations.
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