Eli5 : Why do some genes (like skin color) mix and shade upon inheritance while some don’t (like eye color) ?
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Certain parts of the year, I turn darker. When I go to Florida, I turn a little darker, a shade darker. Most of the time I carry myself in a mocha tone, but there are some parts of the year when I’m more mahogany.
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.
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.
Certain parts of the year, I turn darker. When I go to Florida, I turn a little darker, a shade darker. Most of the time I carry myself in a mocha tone, but there are some parts of the year when I’m more mahogany.
Two different mechanism exist which determine the color of an object we perceive.
The first is controlled by pigments like melanin as mentioned in other comments. Pigments absorb certain wavelengths of light and reflect others. We then see the reflected light. Our skin gets darker when a higher pigment concentration absorbs more light.
The second mechanism is light scattering. Think of it as physical nano structures that bend light into other wavelengths. Blue pigment is very rare in animals and most get their blue color this way. Some fish and amphibians are the exception.
The human iris gets it’s color via a combination of both.
A bunch of genes influence the pigment production. If you get a high yielding set form at least one parent, most of the light is absorbed by pigments and you’ll have brown eyes. Barely any light is left to scatter.
Blue and grey eyes are where you produce less pigment so only a bit of the light is absorbed and the rest scattered. Grey is rarer because it requires more specific scattering.
Green and hazel eyes lie in between. Green is so rare because it needs just the right amount of pigmentation.
Amber may look like hazel but is produced by a specific combination of pigment concentrations and less a result of scattering. Hence it’s the third rarest after grey and green.
No pigments at all means the light goes straight through to be reflected by blood vessels causing the red eyes characteristic for albinism.
Two different mechanism exist which determine the color of an object we perceive.
The first is controlled by pigments like melanin as mentioned in other comments. Pigments absorb certain wavelengths of light and reflect others. We then see the reflected light. Our skin gets darker when a higher pigment concentration absorbs more light.
The second mechanism is light scattering. Think of it as physical nano structures that bend light into other wavelengths. Blue pigment is very rare in animals and most get their blue color this way. Some fish and amphibians are the exception.
The human iris gets it’s color via a combination of both.
A bunch of genes influence the pigment production. If you get a high yielding set form at least one parent, most of the light is absorbed by pigments and you’ll have brown eyes. Barely any light is left to scatter.
Blue and grey eyes are where you produce less pigment so only a bit of the light is absorbed and the rest scattered. Grey is rarer because it requires more specific scattering.
Green and hazel eyes lie in between. Green is so rare because it needs just the right amount of pigmentation.
Amber may look like hazel but is produced by a specific combination of pigment concentrations and less a result of scattering. Hence it’s the third rarest after grey and green.
No pigments at all means the light goes straight through to be reflected by blood vessels causing the red eyes characteristic for albinism.
Two different mechanism exist which determine the color of an object we perceive.
The first is controlled by pigments like melanin as mentioned in other comments. Pigments absorb certain wavelengths of light and reflect others. We then see the reflected light. Our skin gets darker when a higher pigment concentration absorbs more light.
The second mechanism is light scattering. Think of it as physical nano structures that bend light into other wavelengths. Blue pigment is very rare in animals and most get their blue color this way. Some fish and amphibians are the exception.
The human iris gets it’s color via a combination of both.
A bunch of genes influence the pigment production. If you get a high yielding set form at least one parent, most of the light is absorbed by pigments and you’ll have brown eyes. Barely any light is left to scatter.
Blue and grey eyes are where you produce less pigment so only a bit of the light is absorbed and the rest scattered. Grey is rarer because it requires more specific scattering.
Green and hazel eyes lie in between. Green is so rare because it needs just the right amount of pigmentation.
Amber may look like hazel but is produced by a specific combination of pigment concentrations and less a result of scattering. Hence it’s the third rarest after grey and green.
No pigments at all means the light goes straight through to be reflected by blood vessels causing the red eyes characteristic for albinism.
Eye color is determined by the level of the same pigment in your iris, that also affects the color of your skin: melanin.
The key difference is the mechanism of how that color is manifested. With your skin, melanin absorbs most colors of light, and reflects back what’s left. Usually a shade of tan/brown, which can range from very light to very dark.
Your eyes are a bit different. Some of the light is absorbed by the melanin, but unlike your skin, the light that hits your iris also travels through your cornea and lens, which refracts (bends) the light, an also scatters it a bit, dissipating some other colors of light. Your resulting eye color is the sum of these effects.
Lens and eye size/shape aside, changing the amount of melanin *does* effect eye color, which we do see in a lot of cases. Eye color can change between infancy and older ages, as melanin production increases. Some peoples’ eye color even change subtly with the seasons, between summer and winter, as the amount of melanin they produce fluctuates.
Eye color is determined by the level of the same pigment in your iris, that also affects the color of your skin: melanin.
The key difference is the mechanism of how that color is manifested. With your skin, melanin absorbs most colors of light, and reflects back what’s left. Usually a shade of tan/brown, which can range from very light to very dark.
Your eyes are a bit different. Some of the light is absorbed by the melanin, but unlike your skin, the light that hits your iris also travels through your cornea and lens, which refracts (bends) the light, an also scatters it a bit, dissipating some other colors of light. Your resulting eye color is the sum of these effects.
Lens and eye size/shape aside, changing the amount of melanin *does* effect eye color, which we do see in a lot of cases. Eye color can change between infancy and older ages, as melanin production increases. Some peoples’ eye color even change subtly with the seasons, between summer and winter, as the amount of melanin they produce fluctuates.
Eye color is determined by the level of the same pigment in your iris, that also affects the color of your skin: melanin.
The key difference is the mechanism of how that color is manifested. With your skin, melanin absorbs most colors of light, and reflects back what’s left. Usually a shade of tan/brown, which can range from very light to very dark.
Your eyes are a bit different. Some of the light is absorbed by the melanin, but unlike your skin, the light that hits your iris also travels through your cornea and lens, which refracts (bends) the light, an also scatters it a bit, dissipating some other colors of light. Your resulting eye color is the sum of these effects.
Lens and eye size/shape aside, changing the amount of melanin *does* effect eye color, which we do see in a lot of cases. Eye color can change between infancy and older ages, as melanin production increases. Some peoples’ eye color even change subtly with the seasons, between summer and winter, as the amount of melanin they produce fluctuates.
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