Blog Response to Oct. 8

 There are three types of selection to be discussed today.

1. Directional Selection

    This occurs when the extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype. In the example drawn, the shark is looking for a tasty dinner. He swims over by a coral reef where a red fish and an orange & purple fish are trying to hide from him. In this case, the red fish blends in well enough to survive, while the orange & purple fish is not hidden enough and will be the shark's dinner. Therefore, the phenotypic frequency is shifted toward the population of the red fish. 



2. Stabilizing Selection
    
    Stabilizing selection occurs when the average phenotypic frequency is favored, rather than either of the extremes. An example of this occurs in birds. When birds lay eggs, the number of offspring they produce is called "clutch size." Birds want to lay as many eggs as possible to maximize her number of offspring. However, studies have shown that the more offspring produced, the decreased chance that each individual will survive due to decreased parental care and resources. For example, if a female bird were to only lay one egg, that egg would have about a 90% chance of survival, but if she had 10 offspring, each individual offspring would have about a 10% chance of survival. Therefore, in this case the optimal number of offspring produced would be around 5 so each individual would have about a 50% chance of survival. 




 
Average & Favored clutch size



3. Disruptive Selection

                Disruptive selection occurs when either phenotypic extreme is favored, rather than the average phenotypic frequency. Therefore, the variance of the trait increases and the population is divided into two distinct groups. 



Comments

  1. Amanda CzapkayOctober 20, 2020 at 9:03 AM

    I like the images you added and the examples used for the different types of selection. That definitely helps me understand it more. I think we are also supposed to include positive and negative frequency dependent selection in our blog posts! I could be wrong but I think she also covered those in the lectures as well.

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