"Color blindness is common in humans-up to 8 percent of Caucasian males are color-blind due to abnormalities in their X-linked red/green opsin genes. However, in the wild, color blindness is very rare. A study of 3153 macaque monkeys revealed only 3 color-blind individuals (less than 0.1 percent). Given the high frequency of color blindness in humans (where color vision is certainly under less intense selection now, if at all) and the low frequency of color blindness in the wild macaque, this suggests that selection is maintaining color vision in these monkeys and other trichromatic species," (Carroll 105). To review and understand why a male is more likely to receive the mild disorder (color-blindness), please read Campbell page 278.
If color blindness is increasing, albeit a rare disorder inherited as a sex-linked trait, why has natural selection relaxed (Carroll 123) upon these genes (opsins MWS and LWS) that lead to the development of color vision? How could natural selection contribute to creating these genes into fossil genes? Could natural selection be relaxed more upon sex-linked genes causing greater disruptions through evolutionary history because males receiving one copy of their X-chromosome from their mother could receive disorders much more easily?
Most mammals are nocturnal and thus the need for color vision is not truly a selective advantage as opposed to having rhodopsin (Caroll 123-124). If humans are diurnal, why is there a greater loss of color vision as it may provide a selective advantage?
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The reason why color-blindness is so common is because of the lack of selective pressure on humans today. While color-blindness may have meant death for a caveman in the old days, a color-blind person has no trouble surviving today. This is similar to the growth in lactose intolerance: a disability or genetic disorder no longer prevents a person from reproducing. While color vision certainly is useful, it really isn't necessary for life now.
ReplyDeleteI believe that color-blindness could possibly become a fossil gene one day. Since we no longer "need" color vision, a man's opsin genes may mutate, resulting in colorblindness. Then, since color-blindness won't affect his chances at reproduction, his mutated opsin genes will be passed down to his kids. Over time, the opsin gene will fossilize in his family, since there won't be any selective pressure on maintaining color vision.
I don't think the normal red-green color-blindess will fossilize any genes because it's a result of sex-linked genetic disorders. While definitely kinder to girls, the chance of inheriting this color-blindness doesn't change.
Many other animals such as birds have a great need for color vision. Their color vision is used to be able to distinguish prey from far distances. Humans also have great need for color vision although it is not as apparent as it is in other animals. Many times humans use their color vision to help them to better learn information. For example, it is common in ap bio for Ms. I to use different colors in her powerpoint to help us to remember certain concepts better. It is a color tool for many students. Color vision is also fairly important for humans in terms of mating. You often hear “look at his beautiful eyes” or “I love her blonde hair”. It is a way to differentiate all humans and also in mating there is a certain aspect of attraction that uses the differences in color. Also, color helps humans to identify dangers. For example, if a person is walking and feels their nose is wet and feels it how would they know if it is mucus or blood. Both blood and mucus can be thick and thin and could be hard to identify without color. However, we treat the two options very differently. Colors are constantly being used in science to identity the differences between difference substances in chemistry. Also, color is typically used in medicine to distinguish between gram positive and gram negative bacteria, and are constantly used to make medical diagnosis’s. Humans are able to be as technological as they are because of their abilities to see color. If humans lost this ability they would no longer be able to function with the same efficiency. Therefore, color vision will not become a fossil gene in humans.
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