Module 8 Discussion Prompt

 Genetic Variation 

Natural Selection and evolution are believed to eliminate genetic variation and fixate certain genes in populations. Natural selection selects for specific genes and these genes are supposed to become fixated in a population, so why do we not see a loss in genetic variation? 

One reason is that the heterozygote trait is selected for. We see this in people with sickle-cell anemia. In places with malaria, sickle-cell anemia is seen as an advantage to protect against it. Sickle-cell anemia is a blood disease that cause sickle-shaped red blood cells. However, people with sickle-cell anemia are protected from malaria. The heterozygote trait is selected for because the individual still had immunity to malaria and they tend to not have the severe effects of sickle-cell anemia. In this case, genetic variation will continue in the population because the dominate and recessive genes are needed. 

Another reason could be negative frequency-dependent selection. Negative frequency-dependent selection is when a trait starts to become common, it starts getting selected against and the rare trait get selected for. This type of selection promotes genetic variation because the selection is constantly changing between different traits. This can be seen in viruses a lot. Once a certain strain becomes common, hosts start fighting off the common strain. This makes the rarer strain selected for, but as that one becomes more common, a new strain starts getting selected for. This creates a cycle that promotes genetic variation. 

One last reason that can explain genetic variation is migration. When individuals migrate to a different place, they bring their different genes with them. If they mate with individuals in this new population, they will introduce new genes to the population. This promotes genetic variation. 

There are other reasons as to why we do not see a complete loss in genetic variation during natural selection and evolution. However, I mentioned 3 different ways from the past modules that we have learned about. Those 3 include selection of the heterozygote, negative frequency-dependent selection, and migration.