Red hair raises more genetic complexities than was once thought. Previously, variations in a single gene, MC1R, were thought to be decisive. But lately, it has become clear that other genetic factors interact with MC1R to determine whether one’s locks will be “ginger” or something else. To get to the roots of the matter, scientists based at the University of Edinburgh mapped the genes responsible for hair color among UK Biobank participants—a population of nearly 350,000 people.

Comparing redheads to people with brown or black hair, the scientists, led by the University of Edinburgh’s professor Ian Jackson, Ph.D., identified eight previously unknown genetic differences that are associated with red hair. The scientists also looked at the functions of the genes they identified and found that some of them work by controlling when MC1R is switched on or off.

Additional details appeared December 10 in the journal Nature Communications, in an article titled, “Genome-wide study of hair colour in UK Biobank explains most of the SNP heritability.” Besides identifying eight additional variants that explain most of the SNP heritability of red hair, the study found that more than 200 genetic variants are independently associated with multiple hair colors on the spectrum of blond to black.

“MC1R explains only 73% of the SNP heritability for red hair in UK Biobank, and in fact most individuals with two MC1R variants have blonde or light brown hair,” the article’s authors indicated. “We identify other genes contributing to red hair, the combined effect of which accounts for ~90% of the SNP heritability.”

Also detailed were the differences in the 200 genes associated with blondes and brunettes. The researchers were surprised to find that many of these 200 genetic differences were associated with hair texture rather than pigmentation. Others are involved in determining how the hair grows—whether curly or straight, for example. This finding, the scientists pointed out, emphasizes the importance of the keratinocyte-melanocyte interactions in the determination of hair pigmentation and the impact of hair shape on color perception.

“We were able to use the power of UK Biobank, a huge and unique genetic study of half a million people in Britain, which allowed us to find these effects,” noted Dr. Jackson.

Melanie Welham, executive chair of the Biotechnology and Biological Sciences Research Council (BBSRC), commented on the study as follows: “Once again, collaborative research is helping to provide answers to some of life’s important questions. BBSRC is pleased to have helped support the largest genetic study of human hair color. It has provided some fascinating insights into what makes us such distinct individuals.”

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