Question

Assume that a certain population is free of all evolutionary forces except for natural selection. A particular recessive allele is known to confer a selective disadvantage when expressed in recessive homozygotes. In going from one generation to the next, the frequency of the dominant counterpart to this allele shifts from 0.2 to 0.3. 4. a. What is the selection coefficient for the homozygous recessive genotype? (4 points) b. What is the frequency of the dominant allele in generation 3? (4 points) c. What are the genotype frequencies in the third generation? (3 points)

Answer 1

a) If the population size remains same and reproductive rate differ then fitness of a homozygous recessive populatiom=0.50

                   selection coefficient=1-w(w=fitness)

                                                = 1-0.50

                                                =0.50

b) Since recessive gene frequency=0.3 the let us consider it as q

p+q=1 so p+0.3=1 and q=1-0.3=0.7 so frequency of dominant allele is 70%

c)Frequency of dominant homozygous=6/9=0.67

Frequency of heterpzygous=1/9=0.11

Frequency of homozygous recessive=2/9=0.22