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In this lesson you will learn about one of the aspects of nature that makes evolution possible: mutation.

Specifically, we’ll look at the difference between spontaneous and induced mutations.

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Genetic Change

Think about how different reptiles look now than they did during the time of the dinosaurs. This is a result of evolution, or change over time, and it is an ongoing part of nature.

There are several different mechanisms that move evolution along and help create the changes we see throughout natural history, but arguably the most influential of these mechanisms is mutation. Mutation happens when the genetics of an organism are altered, which produces a change in how the organism looks or acts.One famous example of mutation is in fruit flies (Drosophila melanogaster).

Fruit flies are periodically born with different eye colors or wing shapes, and it is easy to study them because they have such a short life cycle. Fruit flies have been studied as part of both of the two main types of mutation: spontaneous mutation, which occurs naturally, and induced mutation, which is purposefully set in motion by humans.

Spontaneous Mutation

Spontaneous mutations get their name because they are unpredictable.

New spontaneous mutations are not particularly frequent, and scientists are not sure exactly how they work or what causes them. These mutations occur naturally, without human interference.There are several factors that can influence spontaneous mutation. These include natural sources of radiation, such as UV rays from the sun.

Heat can also cause mutation. Sources that can cause mutations are known as mutagenic agents. In some cases, it’s not easy to pinpoint the mutagenic agent for a spontaneous mutation.One example of spontaneous mutation is the appearance of sickle cell anemia in humans.

It occurs naturally, and it has stuck around for new generations because it is beneficial to carry the sickle cell anemia gene in areas with high incidence of malaria. Malaria does not affect carriers of sickle cell, thereby giving those with sickle cell anemia immunity against malaria, which kills over one million people every year.

Induced Mutations

Due to their infrequent and unpredictable nature, spontaneous mutations are not a reliable source for scientists who want to study mutations and how they work.

Induced mutations are a solution to this issue. Induced mutations are purposefully started (they are induced) by exposing living tissue to mutagenic agents. Scientists often do this simply to measure rates and incidences of mutation.Mutations can be induced using physical agents, such as X-rays or UV rays, or chemical agents, such as mustard gas and formaldehyde. For the most part, induced mutations appear as point mutations, especially if they are caused by chemical agents. Point mutations are when one part of a base pair of DNA is changed.

Deletion is another type of mutation. This is when part of a chromosome pair is completely removed.Fruit flies were the subjects of one of the earliest induced mutation experiments because of their short lifespan and ease of observation. H. J.

Muller exposed fruit flies to X-rays, and he noted that the rate of mutation increased as the fruit flies were exposed to more X-rays.

Lesson Summary

One way that evolution proceeds is through mutation, and there are two overarching types of mutations. The first is spontaneous mutation. This type occurs naturally, and it is infrequent and unpredictable. It might be affected by several different naturally occurring mutagenic agents, such as UV rays or heat. Sickle cell anemia is an example of a spontaneous mutation that stuck around to future generations because it is occasionally beneficial. The other type of mutation is induced mutation.

These are purposefully started by exposing living tissue to mutagenic agents. Physical agents include X-rays and UV rays, while chemical agents include mustard gas and formaldehyde. Point mutations are most common with induced mutations, especially those done with chemical agents. Point mutations happen when one half of a base DNA pair is changed.

Deletion, where part of a chromosome is removed, might also occur. Fruit flies are used to study both types of mutation because they have very short life spans, so the effect of mutation is easily observable across generations.

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