How Many Colors Can You See?

Normal people are trichromatic.  They have three cones in their eyes (blue, green and red) that can identify about 100 different gradations of color.  The brain then combines those colors in variation, enabling the average person to distinguish about 1 million different colors.

(Most animals are dichromatic, meaning they have two optical cones.  Humans and some other primates are trichromatic.  Certain fish, birds and insects are tetrachromatic, meaning they have four optical cones.)

What would it be like for a human to be tetrachromatic?  About 2 percent of women – almost 100 million around the world – actually have this rare gift.  These females have a fourth optical cone between the red and green cones, enabling them to see about 100 million different colors.

Only women can be tetrachromatic, as the necessary genes are only found on the X chromosome.  (Women have two X chromosomes, while men have one X and one Y.)

Conversely, about 8 percent of men have an opposite problem: color deficiency, also known as color blindness.  In this case, a man inherits two red or two green cones in addition to the blue one.  This makes it difficult for him to distinguish between red and green.  Interestingly, a color-deficient male may be more likely to have a tetrachromatic mother, due to the way genes are inherited.

A recent study by neurologists found that women are better than men overall at distinguishing subtle differences in colors.

Gene therapy may someday be able to help those with genetic eye diseases or defects.  Scientists were able to restore rod and cone vision in dogs afflicted with retinal degeneration using gene therapy.  An Agilent high-performance liquid chromatograph and array detector were used in the research.

This information is for research purposes only.  It is not intended for any use in diagnostic procedures.


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