Help with AP Biology please? About phenotypic polymorphism.
If a phenotypic polymorphism lacks a genetic component, then natural selection cannot act upon it to make a population better adapted over the course of generations.
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Polymorphisms, or variations in appearance, can be genetic or environmental in origin. An environmental polymorphism is also known as a polyphenism. While the underlying mechanism for the polyphenism is of course in the genes, the environment determines the outward appearance, so that individuals with the same allele can present different phenotypes, depending on the conditions they are exposed to.
A common example of polyphenism would be temperature dependent sex determination, which is seen in some reptiles. In this case, the gender of the animal is determined not by genetics, but by the temperature at which the eggs are incubated.
Another example is seasonal polyphenism; many birds and animals exhibit different plumage or antlers during mating season, or change pelt color to better blend in with the environment as the seasons change.
Since natural selection acts solely by changing the frequencies of alleles in a population, it does not affect polyphenisms, where the variants are all the result of the same alleles. An individual with a different allele might be subject to natural selection, however; for instance, an arctic fox who did not turn white in the winter might not be as successful as its peers, but that fox would not be an example of polymorphism, it would be a mutation.
Polymorphism is a natural occurence within species that allows for different forms of the same species to exist. Think about hair color ,for example. The four basic hair colors for human hair are black, brunette (brown), blonde, and red. Then, there are variations, in-betweens, combinations of those four basic hair colors. It is all hair, but it is different forms of hair color. This trait is expressed physically as a result of that persons genotype, the genetic code in their DNA that expresses for the specific hair color. So expecting to get a child that has a completely different hair color from two parents who have similar hair colors doesn't make much sense, since the offspring gets their genetic makeup from the two parents. The genotype, what you are calling the genetic component, is the mechanism that produces the phenotype, the physical trait being observed. Without the correct genotype, the phenotype can not naturally exist, much less be passed on to future generations.
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