Changing just one letter of genetic code is enough to generate blonde hair in humans, according to a new analysis from researchers at the Howard Hughes Medical Institute in Chevy Chase, MD. David Kingsley, of the Howard Hughes Medical Institute, has been studying the evolution of sticklebacks – the small fish that moved from the seas to colonize lakes and streams at the end of the last Ice Age – for the last 10 years. Using the sticklebacks’ adaptive responses to different habitats as a case study, Kingsley and his colleagues have been able to identify molecular-level changes responsible for driving evolution. More recently, they have turned their attention to see how evolutions in the stickleback might apply to other species, such as humans. The research that led Kingsley’s team to investigate the genetic code responsible for hair color initially concerned changes in stickleback pigmentation. As part of a 2007 study, they found that a change in the same gene had driven pigmentation changes in different populations of sticklebacks around the world. Interestingly, they found that this genetic change was not unique to the stickleback.

Same gene in sticklebacks and humans controls pigmentation “The very same gene that we found controlling skin color in fish showed one of the strongest signatures of selection in different human populations around the world,” Kingsley says. Share on Pinterest The genome “is littered with switches,” the researchers suspect. Different versions of this gene – called “Kit ligand” – in humans are associated with differences in skin color. In both fish and humans, Kingsley found, the genetic changes thought to be responsible for pigmentation differences take place in regulatory elements of the genome. “It looked like regulatory mutations in both fish and humans were changing pigment,” Kingsley says. But tracking down specific regulatory elements in the whole genome is like finding a needle in the proverbial haystack. “We have to be kind of choosy about which regulatory elements we decide to zoom in on,” Kingsley acknowledges. As well as encoding a protein that develops pigment-producing cells, however, Kit ligand has many other functions. For example, it influences the behaviors of blood stem cells, sperm or egg precursors and neurons in the intestine. The team was interested in seeing whether they could isolate the regulatory changes in Kit ligand responsible for hair color without affecting any of the gene’s other functions.