What causes colorblindness?

Colorblindness is usually a genetic condition passed on the X chromosome from mother to son. It affects up to one in 10 men and one in 100 women. The most common form is the inability to distinguish red from green (that's why traffic signals are always in the same order every where). Colorblind people are banned from such jobs as fighter pilots and police officers -- and (we hear) from picking out their own clothes. Take a test using the circles below.

Normal people should see A=8, B=5, C=29, and D=74. Color deficient people may see A=3, B=2, C=70, or D=21. » Continue reading

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