Book2-Unit3-TextC..doc

Unit 3 Gene: a Miracle Text C Some Women May See 100 Million Colors, Thanks to Their Genes 1 Susan Hogan can’t be sure, but it wouldn’t surprise her if she turned out to be a tetrachromat. 2 A tetrachromat is a woman who can see four distinct ranges of color, instead of the three that most of us live with. 3 A genetic test would be needed to verify whether Mrs. Hogan truly fits that description, but it could help explain why the interior decorator can hold up three samples of beige wall paint, “and I can see gold in one and gray in another and green in another, but my clients can’t tell the difference.” 4 It may be impossible for us trichromats to imagine what a four-color world would look like. But mathematics alone suggests the difference would be astounding, said Jay Neitz, a renowned color vision researcher at the Medical College of Wisconsin. 5 Each of the three standard color-detecting cones in the retina—blue, green and red—can pick up about 100 different gradations of color, Dr. Neitz estimated. But the brain can combine those variations exponentially, he said, so that the average person can distinguish about 1 million different hues. 6 A true tetrachromat has another type of cone in between the red and green—somewhere in the orange range—and its 100 shades theoretically would allow her to see 100 million different colors. 7 That may be why Mrs. Hogan can look out the windows of her Mount Washington home and tell the relative depths and silting of the three rivers at the Point by discerning the subtle differences in their shades. 8 “I have a very hard time even giving names to colors because I see so many other colors inside them,” she said. 9 Dr. Neitz, who conducts his research with his wife Maureen, said only women have the potential for super color vision. 10 That’s because the genes for the pigments in green and red cones lie on the X chromosome, and only women have two X chromosomes, creating the opportunity for one type of red cone to be ac