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To be color blind means to have a condition called color blindness, an inability to distinguish between colors. It is a sex-linked recessive genetic disorder, so men are more likely affected than women, and it is present from birth. However, the symptoms of color bindness may also arise when there is damage to the eye, particularly the retina, rendering a person unable to dinstinguish between colors later in life.

Types of Color Blindness

In the back of the eye, along the retina, are light receptors called rods and cones that communicate to the brain via the optic nerve. Rods detect light regardless of wavelength. These receptors help the brain determine light intensity as bright or dim. Cones consist of red, blue, or green wavelength detectors and are active in bright light. Each type detects a particular wavelength of light. Color blindness results when a person lacks a particular type or types of cones, or if a particular set is non-functioning.

The most common form of color blindness is red-green color blindness, meaning that a person can not distinguish between the two colors. The brain sees both as the same color, and which color depends on which cones are deficient. The disorder is actually categorized as a disability because it can hinder activities, particularly those requiring discernment of color or the reading of signs from a distance. There are many simple tests to determine if a person is color blind that consist of colored dots making a shape among dots of another color - red and green or, in some cases, blue and yellow. Most people do not know they are color blind until an event occurs where their inability to distinguish between the colors is pointed out.

The Genetics of Color Blindness

The genes encoding the cones are on the X chromosome, which is transmitted differently to males and females, thus the term sex-linked disorder. Since males only inherit one X chromosome, they receive the recessive gene from their mothers. Women need to receive both X chromosomes with a mutant gene from both parents. The heredity breaks down as follows:

-If a mother is a carrier, her sons have a 50% chance of receiving the X with the mutation and being color blind, but their sisters would not be color blind unless their father was as well. However, the daughters have a 50% chance of being carriers.

-If a mother is color blind then her sons will definitely be color blind and her daughters have a 50% chance of being so as well (Any daughters who are not color blind will be carriers). If their father is also color blind, then all children will be.

-If a father is color blind and the mother is not, then the daughters will be carriers. If the mother is a carrier, then they have a 50% chance of being color-blind, as mentioned above.

Learn more about this author, Alicia M Prater PhD.
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