Hair color is determined by the influence of more than a dozen genes, according to our partner The Conversation.
People with red hair have much more pheomelanin, those with dark hair have higher levels of eumelanin, and blonde hair is due to low amounts of both pigments.
The analysis of this phenomenon was carried out by Frida Lona Durazo, postdoctoral researcher in Computational Genetics at the University of Montreal.
Hair color is often used to describe people's physique.
Hair is a good descriptor because it varies a lot from person to person.
Melanin is the molecule responsible for the many shades of color in our hair.
It is also responsible for the color of our skin and eyes.
It is a complex process that causes us to inherit these characteristics from our parents.
Understanding how our genetic information produces different hair shades can be as difficult as disentangling long hair after several days without brushing it.
Although certain genes are known that determine the undertones of hair colors, recent studies in the UK and Latin America with large cohorts of people have shown that there are more than a dozen genes that influence hair color.
In a recent article published in
Communications Biology
, my colleagues and I studied genes associated with hair color in a group of nearly 13,000 Canadians of European descent.
Our results provide information on the genetic variants that can determine different hair colors.
Types of melanin
Melanin is made by a specific cell called a melanocyte which is found in the skin, eyes and hair follicles.
It is also present in the brain.
The type and amount of melanin and how it is distributed in cells is responsible for the different color shades of hair, skin and eyes.
Melanocytes produce melanin, which influences the color of our skin and hair © Setijanti HB, Rusmawati E., Fitria R., Erlina T., Adriany R. & Murtiningsih - CC BY (via The Conversation)
Melanoma, a type of skin cancer, is caused by an overgrowth of melanocytes in the skin.
There are two main types of melanin in our hair: eumelanin and pheomelanin.
Eumelanin is considered the brown-black pigment, while pheomelanin is the red-orange pigment.
People with red hair have much more pheomelanin, those with dark hair have higher levels of eumelanin, and blonde hair is due to low amounts of both pigments.
The main difference that determines which of the two types of melanin is synthesized is in a protein called the melanocyte stimulating hormone receptor, or MC1R.
Variants of the MC1R gene that cause loss of protein function can affect pheomelanin production.
On the other hand, there are many genes in our genome that influence the variations of eumelanin.
Molecular structure of eumelanin © Roland Mattern / Wikimedia CC BY-SA 4.0
The complexity of genetics
In our research, we used genome-wide association studies (GWAS) to identify genetic regions associated with hair color in our autosomal chromosomes.
GWAS find the overlapping associations in a gene of interest or other functional genomic elements.
This method also detects associations in intergenic regions, DNA sequences located between genes.
But correlation does not equal causation.
Therefore, we have attempted to locate genetic variants within or near genes of interest that are more likely to influence hair color.
This helps us to better understand the molecular mechanisms involved in pigmentation.
We have identified genetic variants that had previously been reported, such as those that damage the function of MC1R, which causes a decrease in eumelanin production or can even switch to pheomelanin production.
Other genetic variants that are known to be associated with hair color and pigmentation in general do not alter the structure or function of the protein.
Rather, they regulate the expression of the gene, which means that they control the amount of protein produced.
Vitiligo is a benign genetic disorder that affects melanin production © Shutterstock (via The Conversation)
One can take as example a genetic variant located near the OCA2 gene for which the expression of the OCA2 gene decreases in the presence of guanine, a constituent element of DNA.
This results in less production of melanin.
We also investigated whether these regions of interest share genetic markings related to DNA methylation - which can regulate gene expression - in melanocytes.
We have observed that the DNA methylation state may be a relevant process in the regulation of pigmentation in certain genomic regions.
More research is needed to provide concrete evidence on this.
The ways of pigmentation
By studying the genetic factors that determine hair color, we can better understand how pigmentation occurs.
This helps us better understand pigmentation diseases and their genetic risk factors, such as the role of pigmentation in skin melanoma and vitiligo.
Our "GENETICS" file
Another interesting avenue is the improvement of predictive models of hair color from a DNA source, which has an impact on forensic DNA phenotyping in police investigations by making it possible to predict the appearance of a person from forensic samples.
The inclusion of other population groups in hair color research will give us the opportunity to identify new genes and to better understand the mechanisms of pigmentation.
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This analysis was written by Frida Lona Durazo, postdoctoral researcher in Computational Genetics at the University of Montreal.
The original article was published on The Conversation website.
Declaration of interests
Frida Lona Durazo does not work, advise, own shares, receive funds from any organization that could benefit from this article, and has not declared any affiliation other than her research organization.
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