Mixed Race Studies

An Unexpectedly Complex Architecture for Skin Pigmentation in Africans

Cell
Volume 171, Issue 6, 2017-11-30
pages 1340–1353.e14
DOI: 10.1016/j.cell.2017.11.015

Alicia R. Martin, Meng Lin, Julie M. Granka, Justin W. Myrick, Xiaomin Liu, Alexandra Sockell, Elizabeth G. Atkinson, Cedric J. Werely, Marlo Möller, Manjinder S. Sandhu, David M. Kingsley, Eileen G. Hoal, Xiao Liu, Mark J. Daly, Marcus W. Feldman, Christopher R. Gignoux, Carlos D. Bustamante, Brenna M. Henn

Highlights

• Skin pigmentation in Africans is far more polygenic than light skin in Eurasians
• Southern African KhoeSan populations have lighter skin compared to equatorial Africans
• Highly heritable KhoeSan skin color variation is poorly explained by known genes
• The study of African skin color identifies novel and canonical pigmentation genes

Approximately 15 genes have been directly associated with skin pigmentation variation in humans, leading to its characterization as a relatively simple trait. However, by assembling a global survey of quantitative skin pigmentation phenotypes, we demonstrate that pigmentation is more complex than previously assumed, with genetic architecture varying by latitude. We investigate polygenicity in the KhoeSan populations indigenous to southern Africa who have considerably lighter skin than equatorial Africans. We demonstrate that skin pigmentation is highly heritable, but known pigmentation loci explain only a small fraction of the variance. Rather, baseline skin pigmentation is a complex, polygenic trait in the KhoeSan. Despite this, we identify canonical and non-canonical skin pigmentation loci, including near SLC24A5, TYRP1, SMARCA2/VLDLR, and SNX13, using a genome-wide association approach complemented by targeted resequencing. By considering diverse, under-studied African populations, we show how the architecture of skin pigmentation can vary across humans subject to different local evolutionary pressures.

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DNA survey finds all humans are 99.9pc the same

The Telegraph
2002-12-20

Roger Highfield, Science Editor

Whether you hail from Surbiton, Ulan Bator or Nairobi, your genetic make-up is strikingly similar to that of every other person on Earth, an analysis concludes today.

Although scientists have long recognised that, despite physical differences, all human populations are genetically similar, the new work concludes that populations from different parts of the world share even more genetic similarities than previously assumed.

All humans are 99.9 per cent identical and, of that tiny 0.1 per cent difference, 94 per cent of the variation is among individuals from the same populations and only six per cent between individuals from different populations….

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How medicine is advancing beyond race

CNN.com
2011-07-08

Elizabeth Landau, CNN.com Health Writer/Producer

(CNN)—No matter what race you consider yourself to be, you have a unique genetic makeup.

That’s why, as technology improves and researchers explore new implications of the human genome, medicine is going to become more individually tailored in a model called personalized medicine.

Although we’ve been hearing for years that people of particular races are at higher risk for certain illnesses, personalized medicine will (in theory) make better predictions based on actual genetic makeup. And even now, race is less relevant to your own health care than you might think.
 
But doctors say a patient’s culture—the collection of norms, goals, attitudes, values and beliefs—will always be important to health care, no matter how sophisticated genetic technology gets.

Biologically, what is race?

When it comes down to it there’s, no clear-cut way of saying that one person “belongs” to one race or another—in fact, a person who has the skin color and hair type typical of one race may self-identify in a completely different way.

And if you think that race comes from location-based populations, many Americans don’t have a “pure” genetic heritage from only one world region. In fact, 9 million Americans identified as multiracial on the most recent census, so it’s hard to make these distinctions.

You probably have genes that came from several groups of ancestral communities. Based on archaeological evidence, everyone’s earliest ancestors came from Africa more than 2 million years ago, so we’re all descended from the same “race” anyway.

“There are genetic ancestries—markers that you can see—but those don’t necessarily perfectly correlate with what people consider their own race to be, because that’s sort of an artificial construct,” said Dr. Wendy Chung, assistant professor of pediatrics at Columbia University Medical Center…

…Sometimes race obscures underlying mechanisms for genetic traits.
 
For decades, doctors thought that sickle cell disease was exclusively African, but some people of Mediterranean and Indian origin also have the genetic trait. We now know that the genetic trait for sickle cell disease protects against malaria, and that it is found among people with ancestry in places where malaria is, or used to be found, biologists Marcus Feldman and Richard Lewontin point out in their essay “Race, Ancestry, and Medicine.”

Race can also hide underlying social issues—namely, poverty.
 
African-American life expectancy at birth is on average, about five fewer years than white Americans, according to the most recent data from the Centers for Disease Control and Prevention. But Dr. Vicente Navarro at Johns Hopkins University has shown in his research that social class is a bigger driver of U.S. life expectancy than race or gender. He points out in a 1990 Lancet study that the United States is the only Western developed nation that does not report health statistics according to class…

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