A One-Letter Blond


If you're tempted to make a dumb blond joke, don't, because they're obsolete! Turns out, blond hair is determined by a single letter in the three billion letters of the human genetic code, and affects no other trait - not intelligence nor the capacity for fun.

This new discovery came from studies on Sticklebacks, a small fish in various habitats around the world, each group having evolved its own distinct skin color. A gene called the Kit ligand is responsible for the fish's skin pigment which in an earlier study, scientists found also affects skin color in humans, and possibly hair color too.

However, Kit ligand plays other important roles in humans, affecting blood cells and sperm cells. It's actually a mutation in an area affecting the Kit ligand that causes blond hair in Northern Europeans. So how did evolutionary changes occur without affecting Kit ligand's other important functions?

Researchers in the new study decided to isolate this regulatory element and determine how it was different in blonds. Using engineered mice, they were able to identify the single letter change from A to G that creates blonds, while affecting nothing else.

This isn't turning a gene on or off, but rather it shows how a gene can be used slightly differently in just one part of the body. Subtle changes like this one reveal how exquisitely controlled the utilization of genes is regulated and how changes to this system contributes to human diversity.

More Information

Single-Letter Change in DNA Leads to Blond Hair
Newswise ' "A single-letter change in the genetic code is enough to generate blond hair in humans, in dramatic contrast to our dark-haired ancestors."

Gene Study Shows Blond Hair Color Is Just Skin Deep
National Geographic News — "For thousands of years, people have both prized and mocked blond hair. Now, a new study shows that many can thank a tiny genetic mutation'a single letter change from an A to a G among the 3 billion letters in the book of human DNA'for their golden locks."

Single letter of DNA 'defines hair color'
Medical News Today — "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."