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I do not understand how skin color in humans work, even after taking a basic genetics course and reading some on wikipedia.

From what I understand, skin is color based on multiple genes that control melanin and other products that affect appearance of skin. So then their are multiple alleles for "skin color" and also some of these alleles can be varying in their expression/inheritance? based on the other alleles presence?(epistasis)

So then a black person and a white person could have various skin colors (phenotypes?) And the offspring of these children could then have varying offspring as well?

Diagrams would help me maybe in explaining the concept.

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    $\begingroup$ I'm still a little uncertain as to where your question lies. Are you wondering how different melanin types and levels create different skin phenotypes (of any animal, no real reason to limit this to humans), or are you interested in how genetic inheritance effects melanocytes? $\endgroup$ – Atl LED May 26 '15 at 18:27
  • $\begingroup$ I have the same problem. Do you look more into melanin production and how this is regulated or more into the genetic reasons for different skin color? $\endgroup$ – Chris May 26 '15 at 18:33
  • $\begingroup$ @AtlLED Ummm, I want to know the underlying genetic components(how the genes work) more than their product(cells, proteins, etc..) $\endgroup$ – Ro Siv May 26 '15 at 18:51
  • $\begingroup$ This is relatively complicated. $\endgroup$ – Chris May 26 '15 at 19:02
  • $\begingroup$ @RoSiv So is your question "How do genes work?" $\endgroup$ – Atl LED May 26 '15 at 19:25
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The genetics of pigmentation is relatively complicated, as the pathway for the pigmentation (regulation of the pigment production, ratio between the melanins, maturation, trafficking and distribution of the melanins from the melanocytes to other cells) is quite long and also subject to different regulations. All the mutations found to date (at least to my knowledge) affect single parts of this long process (so for example MC1R mutations are affecting whether eumelanin is made, while Rab7 and Rab27a is most likely involved in the distribution of the melanosomes). Not all gene functions in this network have been understood so far.

Population studies have shown that the three main ethnic subgroups (west-africans, asians and europeans) have developed independently from a common ancestor with different (and independent) mutations in each arm. See the figure from reference 1 as an illustration, it also shows the genes involved in each arm:

enter image description here

Pigmentation is a protection against UV light, so there is a strong selection against mutations in areas with high UV light (west africa for example). The general theory is that in areas with less UV light the skin got lighter to allow the production of vitamin D (for which you need UV light). If you want to go through the single genes and their influence on pigmentation, please have a look at this Wikipedia page, which gives a good explanation. Also have a look at the references.

References:

  1. Unpacking Human Evolution to Find the Genetic Determinants of Human Skin Pigmentation
  2. The genetics of pigmentation: from fancy genes to complex traits.
  3. Molecular genetics of human pigmentation diversity
  4. Human pigmentation genetics: the difference is only skin deep
  5. The etiology and molecular genetics of human pigmentation disorders
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    $\begingroup$ This HHMI Biointeractive Video gives one of the better explanations I have seen on the genetics of Human Skin color. The Biology of Skin Color It is actually the destruction of folate, which is known to lead to birth defects and sperm fitness that selects for Eumelanin in regions with high levels of UV. $\endgroup$ – AMR Jan 10 '16 at 23:56
  • $\begingroup$ Ok, several genes are involved, which increases the combinatory. But still, this should give a finite number of genotypes, and thus of phenotypes, right ? -> is the combinatory just large enough (estimation?) so that we have the false impression of continuous shade ? Or is there something else occurring, making the shades really continuous ? $\endgroup$ – Fabrice NEYRET Dec 21 '16 at 9:30

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