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Hair colour: Maybe we’re born with it. Maybe it’s a melanin gene


Roughly, for every redhead, there are three people with black hair, five with blonde, 15 with light brown and 20 with dark brown, according to a new Canadian study

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A vast survey of nearly 13,000 Canadians of European background has uncovered new clues to the genetic causes of hair colour.

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Using data from a massive genetic survey of Canadian volunteers, the study out of University of Toronto at Mississauga identified several possible previously unknown genetic causes for blonde, red and light or dark brown hair. It also offers a good estimate of how those colours are distributed among white Canadians.

Roughly, for every redhead, there are three people with black hair, five with blonde, 15 with light brown and 20 with dark brown, according to the study’s findings.

These colours are what geneticists refer to as phenotypes, the observable or measurable characteristics of an organism, such as a human being. Most phenotypes are determined by the interaction of an organism’s genotype, its set of genes, with the environment and experience.

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But hair colour is curious. It is a genetically controlled expression of pigmentation, like eye colour and skin colour with which it correlates, and one of the few complex human traits that is largely unaffected by a person’s environment.

Hair colour arises from differences in the amount and ratio of melanins in the hair bulb, from which the strand grows. This is a process that is controlled by genetics and has been affected by many different evolutionary factors. The genes that are known to control it, however, do not seem to do so directly, more by regulating other genes.

“We know from recent studies that there are hundreds of variants in many genes involved in this, but sometimes just knowing the gene is not enough information because within one gene you can have mutation, what we call variants,” said lead author Frida Lona-Durazo, who recently completed doctoral research on the biology of hair, skin and eye pigmentation in the Department of Anthropology at the University of Toronto at Mississauga.

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“Our objective was to pinpoint which variants are responsible, even if we know already some genes.”

The researchers did not discover any previously unknown genes, but they were able to “pinpoint other variants in or near genes that have not been described before,” Lona-Durazo said in an interview.

To do this, she and colleagues looked at many complex areas of the human genome that are known to change a person’s hair colour, seeking correlation with self-declared hair colour.

The research focused on people of European background because they show the greatest variation in hair colour. Asian and African populations show variation in hair colour, but the range is narrower, and it is harder to study as a self-reported variable. Ideally, Lona-Durazo said, research could be done on all populations by measuring melanin levels objectively in the lab, rather than asking subjects to report their own hair colour.

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Participants in the new Canadian study were asked to self-report their natural hair colour as falling into one of the five colour categories offered, or to answer “not applicable.” The question specified that this was about hair colour before greying, in which pigmentation declines normally with age.

The data showed interesting regional variations. The proportion of people with black hair from Quebec was much higher than British Columbia, and the proportion of people with red hair from B.C. was much higher than Quebec. Ontario and Alberta’s proportions were very similar, whereas the Atlantic provinces had proportionally more black and dark brown hair and less blonde.

There was a slight sex bias in the number of participants, with about 54 per cent female. But roughly two thirds of people who describe their hair as black were male. All other colour categories were more evenly balanced, male to female. One possible reason for this, according to Lona-Durazo, is a bias among men to say they have black hair and/or a bias among women to say they do not. Another possible factor is that females in general tend to have lighter skin pigmentation, which is correlated with hair colour.

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Variation in hair colour is correlated with variation in eye and skin colour, though not perfectly. Some people with blonde hair have blue eyes, for example, but not all all of them. Also, the global variation in skin pigmentation shows a clear pattern that suggests it is an adaptation to ultraviolet radiation. Hair colour is not so obvious.

“Current evidence indicates that there is a partial overlap in the genetic architecture of hair, eye and skin pigmentation,” according to the paper newly published in Communications Biology.

Much of the interest, beyond pure science, is the application of this knowledge about pigmentation genetics to the understanding of skin cancers. Several genes associated with pigmentation are known to increase melanoma risk, for example.

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This genome-wide meta analyses of hair colour among 12,741 Canadians of European background was made possible by the Canadian Partnership For Tomorrow’s Health, known as CanPath. Using data collected from volunteers, the study’s purpose is to offer health researchers around the world “comprehensive genomic, clinical, behavioural and environmental data on 330,000 Canadians.”

A similar project in Britain in 2018 noted that natural hair colour within European populations is “strikingly variable.” It found “more than 200 genetic variants independently associated with multiple hair colours on the spectrum of blond to black,” and learned that many of those genes are involved in hair growth and texture, not pigmentation. The authors suggested that perceived hair colour in fact arises from the complex interaction of pigmentation and shape, because of different refractive and reflective properties. Strands of blonde hair, for example, tend to be thinner than darker hair.

Curiously, the British study also found the male bias toward black hair, but it also found females were more likely to report blonde or red hair. The Canadian numbers do not seem to show this.

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