Researchers from The University of Western Australia are part of an international team of 45 scientists from seven countries that has identified the genes that determine hair colour.
The study, published in Nature Genetics, confirms that hair colour – one of the most noticeable physical characteristics in humans – evolved through interactions between many different genes.
Managing director and Chair of UWA’s Centre for Ophthalmology and Visual Science Professor David Mackey and colleagues Dr Seyhan Yazar and Dr Alex Hewitt were part of the international research team that identified 123 autosomal and one X-chromosome linked to hair colour.
The genome-wide association study analysed almost 300,000 participants of European descent.
Participants in the Western Australian Pregnancy Cohort (Raine) Study were asked to classify their hair colour at the 20 and 22-year follow-ups. They were asked to define their natural hair colour as fair/blonde, light brown, light red or ginger, dark red or auburn, dark brown, or black.
Combining the Raine data with available genetic data, UWA researchers contributed to the study as one of the cohorts where new genes are identified as genuinely true and not by chance.
Dr Yazar said there were two types of melanin pigment, eumelanin and pheomelanin, which were responsible for giving human hair its colour in combination.
“Pheomelanin is a lighter pigment found in red hair and all humans have some pheomelanin in their hair,” she said.
“Eumelanin, which is further classified into the sub-types black or brown, determines the darkness of the hair colour.”
Dr Yazar said a low concentration of brown eumelanin produced blond hair whereas a higher concentration resulted in brown hair.
“High amounts of black eumelanin result in black hair while low concentrations, in the absence of other pigments, produce grey hair,” she said.
Professor Mackey, who also heads the UWA affiliated-Lions Eye Institute, said twin studies had shown that the amount, ratio and spread of eumelanin and phenomelanin produced in human hair was highly heritable, with inherited factors accounting for 97 per cent of colour variation.
“Until recently, the genetic factors identified in studies had only explained a small portion of hair colour variation,” Professor Mackey said.
“However, using data from the 23andMe Inc customer base, the UK BioBank and the International Visible Traits Genetics Consortium, in which Australian researchers are involved, more than 100 new candidate genes were identified in approximately 300,000 European individuals.
“With these additional genetic factors, we were able to explain 34.6 per cent of red hair, 24.8 per cent of blond hair and 26.1 per cent of black hair inheritance in the study populations.
“Women were more likely to report blonde or red hair than any other colour and less likely to report black hair than men. However, this difference had no impact on distinguishing the identified genetic factors in women and men.”
Dr Yazar said dissecting the pigmentary process that determined human hair colour may allow researchers to develop new genetic tests as well as better understand some rare diseases and skin cancer.