Blondes may indeed have more fun, and suffer the most when it comes to dumb blonde jokes. However, being blonde, natural blonde, is all a matter of a slight DNA tweak that Stanford researchers say is tied to a molecule in stem cell function.
A new Stanford University School of Medicine study states hair color determination is tied to a very tiny DNA change. Research of DNA shows that just one single letter of genetic code, or what researchers say is a "single nucleotide polymorphism" is what makes for a blonde or brunette.
"We've been trying to track down the genetic and molecular basis of naturally occurring traits - such as hair and skin pigmentation - in fish and humans to get insight into the general principles by which traits evolve," said David Kingsley, PhD, professor of developmental biology. "Now we find that one of the most crucial signaling molecules in mammalian development also affects hair color."
According to researchers blonde tresses are due to a DNA change that is tied to a gene encoding a stem cell factor or KITLG. Using mice in experiments, the researchers introduced the gene tweak and there was a significant lighter hair result.
"What we're seeing is that this regulatory region exercises exquisite control over where, and how much, KITLG expression occurs," said Kingsley. "In this case, it controls hair color. In another situation - perhaps under the influence of a different regulatory region - it probably controls stem cell division. Dialing up and down the expression of an essential growth factor in this manner could be a common mechanism that underlies many different traits."
The results also reveal hair color change is not tied to any other human traits such as personality or intellect.
"The change that causes blond hair is, literally, only skin deep," said Kingsley.
The one-letter mutation discovery has nothing to do with hair growth and is part of what scientists once viewed as junk DNA. The gene mutation also doesn't play into eye color or skin color.
"It shows blonde hair doesn't have anything to do with anything but blonde hair," Kingsley said.
The discovery came out of Kingsley's considerable research on stickleback fish. The fish change their coloring depending on water traits.
"The specificity of the [fish] switch shows exactly how independent colour changes can be encoded to produce specific traits in humans," said Kingsley.