Inherited Or Acquired Defect
Most individuals who are color blind inherit the trait. Men are more likely to be color blind because of the way color blindness is inherited. The gene for the trait is located on the X chromosome. Men have one X chromosome and women have two. If a man inherits the gene for the trait, he will have a color vision defect. If a woman inherits a single gene for the trait, she will not, because the normal gene on her other X chromosome will dominate over the defective gene. Women must inherit the defective trait from both parents to be color blind.
Color blindness is a so-called sex-linked characteristic. This means it is a gene that occurs only on the X chromosome, which is passed to the child by the mother. The Y chromosome, which is passed to the child by the father, does not carry the defective gene. This means that children inherit color blindness only from their mothers. Children can inherit color blindness from a mother who is color blind or from a mother who is a carrier of the gene but is not color blind herself. Daughters of men who are color blind will carry the trait, but sons will not.
A more unusual way to become color blind is through disease. Cataracts are the most common cause of acquired color deficiency. In one of the most common eye diseases, cataracts, a cloudy layer in the lens or eye capsule develops. The condition can cause vision to worsen in bright sunlight. Other conditions that may cause acquired color deficiency are retinal and optic nerve diseases.
Medications such as digitalis, a common medication for heart disease, and quinine, medicine for malaria, can also make color perception change. Alcohol has also been known to change the way people see color.
- Color Blindness - Adapting To A Different World
- Color Blindness - Reds And Greens
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