Color blindness is a condition in which different colors appear to be the same color. To understand how this happens, it is necessary to examine how humans actually see colors.
The inner lining of the eyeball is called the retina. The surface of the retina is made up of specialized receptor cells called photoreceptors. There are two types of photoreceptors packed closely together in the retina. The central portion of the retina contains mainly cone-shaped receptor cells (called cones), while the peripheral portion of the retina contains mainly rod-shaped receptor cells (called rods). Whenever a photoreceptor is exposed to light, the photoreceptor produces a barrage of electrical signals. These signals activate a series of nerve cells in a pathway that travels from the eye to the brain.
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Cone vision can differentiate colors, rod vision cannot. The reason for this difference is that all rods respond in the same way to light exposure. However, there are three different types of cones. One type responds more strongly to red light and less to other colors (called red cones) red green color blind test. A second type responds more strongly to green light and less to other colors (called green cones). The third type responds more strongly to blue light and less to other colors (called blue cones). Each spot of color we look at will cause numerous red, green, and blue cones to send signals to the brain. The brain uses the ratio of red cone signals: green cone signals: blue cone signals to determine what color that speck really is. Each shade of color has a slightly different ratio.
However, some people inherit a genetic defect that affects one of the three types of cones. As a result, that type of cone does not work properly. The brain now receives signals from only two types of cones. He still uses the signal ratio to determine the colors. But, due to missing information, several different colors now produce the same ratio. Therefore, the individual sees them as the same color. The most common type of color blindness is called red-green color blindness. In this case, the genetic defect makes it difficult for the person to distinguish between certain shades of red and green. However, there are also other types of color blindness.
Color blindness occurs in men much more often than in women. This is due to the location of the genes responsible for cone vision. The explanation requires some basic information about the genes.
Within the nucleus of a human cell, DNA is present on 46 chromosomes, which can be grouped into 23 pairs. One chromosome in each pair comes from the father, while the other comes from the mother. Each chromosome is made up of thousands of genes. Genes are sections of DNA that contain instructions for making a certain component of the body. Occasionally, a gene undergoes a mutation that changes instructions. In addition to carrying genes, one of the pairs of chromosomes determines the sex of the individual. If this pair consists of two X chromosomes, the individual is a female. But if this pair consists of an X chromosome and a Y chromosome, the individual is a male.
The genes responsible for cone vision are known to be found on the X chromosome. If a mutation has occurred, the instructions for making one of the cone-shaped receptors on the retina may have been changed. Modified instructions can result in a non-functional cone, which could result in color blindness. In a female, the defective gene would have to be present on both of her X chromosomes for her to be color blind. If any of her X chromosomes have normal color vision genes, she will have normal color vision. However, she will be a carrier of color blindness, because she could pass the X chromosome with the defective gene to her child.
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