A One-Letter Blond

Oct. 10, 2014

By Medical Discovery News

Out of the 3 billion letters contained in the human genetic code, all it takes to be born a blond is a single change in a certain place from an A to a G. With the sheer complexity of the human genome, this new discovery shows how remarkably simple it is to be a natural blond. Especially when you consider the lengths people go to become one artificially.

This discovery actually came from research on the evolution of Sticklebacks, small fish that emerged from the oceans and colonized streams, rivers, and lakes at the end of the last Ice Age. Scientists at Stanford University have been studying how Sticklebacks have adapted to different habitats around the world, and particularly how different populations acquired their skin colors. They discovered that changes in a single gene determined the pigmentation of fish throughout the world. The gene responsible, the Kit ligand gene, is also in the human genome. Different versions of it have evolved around the world and are associated with differences in skin color.

The protein encoded in the Kit ligand gene aids in the development of pigment-producing cells, so its role in skin and hair color makes sense. However, the Kit ligand protein plays other important roles elsewhere in the body, such as developing stem cells into blood cells and producing sperm. Therefore, changes to this gene are not simple and could have detrimental consequences. This caused scientists to wonder how such an important gene could evolve while still preserving its essential roles. Both in fish and humans, the changes that lead to differences in pigmentation were not in the genetic region that encodes the Kit ligand protein, but rather at sites in the genome quite distant from here, where elements responsible for regulating that gene are located.

To find the regions that regulate the Kit ligand gene and therefore influence hair color, scientists cut out various regions at a time and linked them to a gene that produces a color when activated. Done in mice, only one of the regions activated in developing hair follicles. Comparing the DNA sequence of that region between brunettes and blonds, they then identified the single A to G change unique to blonds. This change reduced the amount of Kit ligand protein by 20 percent compared to brunettes. Even in mice, when scientists made this genetic alteration, their hair was lighter too. This means that changing a single letter only affects the utilization of the Kit ligand gene in one part of the body – the hair follicles. This region contributes to the diversity of hair color in humans while maintaining the same roles in other parts of the body. As it turns out, being blond is only skin deep.

This work further proves that large regions of our genetic information once thought of as “junk” DNA actually play critical roles. Subtle changes like this reveal how intricately genes are controlled and how even simple alterations are responsible for human diversity. This information can also help us understand how other gene variations may be associated with disease or resistance.

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