Color blindness is a condition in which a person cannot differentiate between certain colors. Those affected cannot distinguish between reds and greens. A few others cannot differentiate between blues and yellows.
The retina is an important part of the human eye and plays a vital role in vision. It includes cells called cones which are innumerable and help the brain to see colors.
About 60 percent are L-cones that see red, 30 percent are M-cones that see green and the remaining are S cones perceiving blue.
Color blindness takes place when cones are absent or when they malfunction. It is generally inherited as a defect in the X chromosome. Since men have only one X chromosome, any defects in that chromosome would affect the resulting male child.
On the other hand, women have 2 X chromosomes. Any defect in one could be negated if the other X chromosome is healthy. It means that a woman can inherit color blindness only if both the X chromosomes have the color blindness trait. Hence, we can safely say that men are more likely to inherit color blindness than women and the chromosome for color blindness comes from the mother.
Although color blindness is primarily inherited, it could take place for other reasons such as brain damage, damage to the retina etc.
Thus, color blindness is sex-linked as it is carried by a sex chromosome, especially an X chromosome. Men have to inherit the gene from their mother to be color blind. But women have to get it from their father too. Color blindness has no bearing on life expectancy. Nor does it affect normal life except for the inability to distinguish colors.
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