Shriver, M. D., E. J. Parra, et al. (2003). “Skin pigmentation, biogeographical ancestry and admixture mapping.” Human
Genetics 112(4): 387-399.
These articles are getting little old, but their findings are interesting and important. They examined the correlation between skin pigmentation and estimated African ancestry. Using a DermaSpectrometer, skin color measurements (melanin index) were taken inner part of arm where the UV rarely hit. African genetic ancestry was estimated using 33 ancestry informative markers (AIMs).
They found that estimated African ancestry was significantly correlated with melanin index, as expected, but more interestingly melanin index and estimated African ancestry vary greatly. This means that functional genes that determine the skin color are located somewhere else on the genome and the allele frequencies of these skin pigmentation gene variants differ greatly between ancestral populations (e.g., Africans and Europeans for African Americans). They explain that because African Americans are recently admixed, we are observing the results of the population structure that existed in their ancestral populations.
Skin color is a very heritable trait. If skin color is determined largely by genes, one may expect to see small variability of melanin index of African Americans with 100% African ancestry, but that is not the case. They observed a great variation in melanin index of African Americans with 100% African ancestry. Because skin color is polygenic traits, there are many different genes that determine the skin color, so natural variation in skin color should exist in Africa.
The research was conducted when only a few candidate genes linked to skin color were found, and they confirmed that two candidate genes for skin pigmentation, TYR and OCA2 are significantly associated with melanin index in African Americans (actually, Shriver and colleagues were working on other projects looking for skin color genes when these articles came
out).
How variable is the skin color and melanin index in Africa? There are research projects that demonstrated that skin color varies among sub-Saharan African populations, but has anybody systematically investigated how variable the skin color is within an African population?
