Natural Science Forum / Biology / Paleontology / July 2004

Variation in Color Vision Genes May Have Helped Humans See the Fruit for the
Trees
Sarah Graham

Eight percent of men experience red-green color blindness, which results
from mutations in genes that code for light-sensitive pigments. But a new
study suggests that even men who aren't color blind may see the world
differently than women do, thanks to natural selection.
Brian Verrelli of Arizona State University and Sarah Tishkoff of the
University of Maryland analyzed genetic data from 236 people from around the
world. Specifically, they studied a gene on the X chromosome known as
OPN1LW, which codes for a protein that detects visible light in the red
spectrum. Exchange of material between this gene and a neighboring gene
associated with green light leads to a high amount of genetic variation but
can result in color blindness if the process goes awry. Among the study
participants the researchers found 85 variants of the gene. "That's
approximately three times higher than what you see at any other random gene
in the human genome," Tishkoff says. "Usually it's a bad thing to have too
much change in a gene, and natural selection gets rid of it. But in this
case we're seeing the reverse."

The increased variation enhances the ability to discriminate between colors
in the red-orange spectrum, particularly among females, because they have
two copies of the X chromosome. Previous research in other primates has
suggested that enhanced red vision in females allows them to better
distinguish between berries and foliage when they are gathering food,
Verrelli explains. If females did the gathering in prehistoric times, as
many experts believe, that may explain why genetic variation promoting color
sensitivity persists today. "We can't explicitly test it, but the model
fits," Verrelli says. The results will appear in the September issue of the
American Journal of Human Genetics. --Sarah Graham

From Scientific American
http://cl.extm.us/?fe8e1c727162067576-fe3016707360067c711779

Posted by
Robert Karl Stonjek.