Blog #4

Describe the three types of selection: directional, stabilizing and disruptive and give an example of each in your own words.

          Directional selection is a type of natural selection where it favors a single phenotype. It occurs in population when there is a shift towards an extreme version of the good trait. An example would be like creating new breeds of dogs over generations. For example, scientists who want dogs who can run fast will look for and select breeds who can run fast, and select the fastest runners from their offspring. Over time, after continuing the process they can produce a dog in a future generation who can run extremely fast.  
          Stabilizing selection is a type of selection where genetic diversity decreases as the population settles on a certain trait. Stabilizing selection favors the normal traits in a population. An example of stabilizing selection is choosing something in the middle, an average point. For example, animals must have certain traits to survive in an environment, so stabilizing selection chooses an average, normal trait for that animal so there are no extremes. The size of an animal would be an example, because in certain habitats, that animal cannot be too big or too small, so stabilizing selection chooses a medium size for that animal.
          Disruptive selection is pretty similar to directional selection; it favors the extreme traits in a population. It is like the opposite of stabilizing selection. It is different from directional selection though, because sudden environmental changes cause sudden forces favoring a particular extreme. Disruptive selection occurs quickly. An example of this would be like the color of an animal. If a mouse had black fur and another had white fur, the offspring could have gray fur. However, the environment they are in may give an advantage to the black and white mice, therefore causing the mouse with gray fur to stand out. As a consequence of the selective environmental pressures the mice population would be disruptively selected for extreme values of the black and white mice, but not the gray mice.