The experiment below is used for answering questions 1 and 2. Using experimental

Question

The experiment below is used for answering questions 1 and 2.

Using experimental populations of mosquitoes, a scientist wished to study the frequencies of two alleles (p = freq. of W1 and q = freq. of W2) of a gene that affects the mosquitos' ability to survive in the presence of a new insecticide.

She set up 10 populations in her lab; all were large enough so that the effects of genetic drift were minor. Five of them (#1-5) were exposed to the insecticide, while the others (#6-10) were not. She started the insecticide-present populations, and the insecticide-absent populations, at different W1 allele frequencies (p = 0.5, 0.1, 0.7, 0.8, and 0.3). After several years and many generations, she re-measured p, the frequency of W1; the results are shown below under "p at end."

    Insecticide        p at start       p at end

1.    Yes                0.5                0.399

2.    Yes                0.1                0.392

3.    Yes                0.7                0.402

4.    Yes                0.8                0.404

5.    Yes                0.3                0.397

6.    No                 0.5                0.502

7.    No                 0.1                0.994

8.    No                 0.7                0.693

9.    No                 0.8                0.806

10. No                 0.3                0.299

Question 1. Of the five "selection scenarios" we discussed in class, which best explains the results?   Explain your answer.

Question 2. Come up with a set of genotype fitnesses for W1W1, W1W2, and W2W2 that, in the presence of the insecticide, would lead to the results shown above, given enough time. Feel free to use the Allele A1 software to check your answer before submitting it. (Note: I am looking for actual numbers here, not symbols. There are many possible correct answers.)

Explanation / Answer

1. Natural selection best explains the case. Genotypes that enable organisms survive and reproduce, in a specific environment, are more common among the individuals that reproduce. These genotypes contribute disproportionately to the offspring of the next generation. Those alleles that increase survival chances or reproduction increase in frequency from generation to generation. Thus, over generations, the individuals of a population adapt beeter to survive and reproduce in the prevailing environment.

Directional selection: The given scenario shows balanced selection in which one allele always has he highest fitness. While in the absence of the insecticide, the frequency of W1 allele remain almost unaltered, its frequency decreased in the presence of the pesticide. This indicates that the other allele has highest fitness than the W1 allele.

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