A new gene study may help explain why she sees crimson, vermillion and tomato, but it’s all just red to him.

In an analysis of the DNA of 236 men from around the globe, researchers found that the gene that allows people to see the color red comes in an unusually high number of variations. And that may be a boon to women’s color perception in particular, study co-author Dr. Brian C. Verrelli told Reuters Health.

That’s because the gene, known as OPN1LW, sits on the X sex chromosome. Women have two X chromosomes, one from each parent, while men have one X and one Y chromosome. Because women have two different copies of the “red” gene, the fact that the gene can have so many variations means it may especially aid women’s perception of the red-orange spectrum.

Verrelli, an assistant professor at Arizona State University in Tempe, and colleague Dr. Sarah Tishkoff report the findings in the American Journal of Human Genetics.

Among the 236 samples of DNA they studied, the researchers found 85 variations in the OPN1LW gene. That’s about three times the number of variations one would see in any other “random gene” pulled from the human genome, Verrelli said.

He noted that past research into color-vision genes has focused largely on variations related to color blindness. The red gene routinely swaps bits of genetic material with its neighbor on the X chromosome, the “green” gene. Sometimes this exchange goes wrong and results in a defect that causes color blindness.

An estimated eight percent of men are color-blind, while few women have the condition because the odds are they will have at least one good copy of the red and green genes.

But the new findings show that variations in the red-perceiving gene are beneficial as well, according to Verrelli. For the many variants to have been preserved throughout evolution, he explained, this diversity must have served a purpose.

He and Tishkoff speculate that the gene variations may have been useful in humankind’s hunter-gatherer days, when sharp color perception may have helped women in their foraging work.

“Today,” Verrelli noted, “it’s not really that important.”

But what is important, according to the researcher, is that studies continue to delve into not only outright genetic defects, but also the common, subtle variations in genes, since they may have significant health effects as well.

SOURCE: American Journal of Human Genetics, September 2004.