Given a detoxification gene with two alleles A and a, allele A is dominant, and

Question

Given a detoxification gene with two alleles A and a, allele A is dominant, and the environment suddenly favors the A allele because of a new insecticide. The allele A has a frequency of 0.2 and a has a frequency of 0.8 as a starting point. Exactly 90% of the aa genotypes die before reproducing (remember the difference between fitness and selection coefficient) and the relative fitness of the heterozygote and of AA is 1 in each case. A. What is the selection coefficient (s) against the aa genotype from the starting generation to the next? B. What is the frequency of A in the next generation of gametes? C. What is the mean fitness in the next generation? D. What is delta p (change in p) from one generation to the next? E. What is the frequency of a in the next generation of gametes? F. Has natural selection occurred? Why or why not? G. Has evolution occurred? Why or why not? H. Has evolution by natural selection occurred? Why or why not?

Explanation / Answer

Answer:

By crossing different homozygotes, Mendel generated plants whose two homologous chromosomes each had a different allele of the gene (Fig. 2.5a). The condition of having two different alleles in a single gene is called heterozygous. All the plants generated from the initial cross (F1 hybrids or F1 generation) would have the same genotype, but could have either one of two different parental phenotypes. In the heterozygous plants, Mendel discovered that certain variants of a trait appeared to mask or cover the expression of other variants. A variant that would cover the other type was termed dominant, while the phenotype that would disappear was called recessive. When we write allele names, we often use uppercase letters for dominant alleles and lowercase letters for recessive alleles. Today we understand that dominant alleles have a sequence of DNA that encodes for a functional protein, while many recessive alleles have changes in the DNA sequence, called mutations, which render the encoded protein nonfunctional. Therefore, in a heterozygous plant, functional and nonfunctional proteins are produced, and the plant has the phenotype of the dominant allele from the functional protein. In Mendel

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