A population of South American Yanomoto indians was exposed to measles. Resistan

Question

A population of South American Yanomoto indians was exposed to measles. Resistance to the disease is given by a resistant allele, PgmS and the other allele in this population, PgmF gives no resistance. The numbers of each genotype in the population before measles exposure are given below, along with the fitness of each genotype.

a. What will be the genotype and allele frequencies in this population after the measles epidemic?

b. No further measles epidemics occur and the next generation of this population also has 2000 individuals. What will be the allele and genotype frequencies in this next generation?

c. Measles returns again, and this next generation is infected. What will be the genotype and allele frequencies in this next generation after this second measles epidemic?

Genotype                FF      FS      SS      Total

Numbers                781     938     281     2000

Fitness                   0        .5       1.0

Explanation / Answer

Answer a: Genotype frequencies after the measles epidemic: SS = 0.375; FS = 0.625 (As explained below)

Allele frequencies after the measles epidemic: S = 0.612; F = 0.388 (As explained below)

Frequency of SS = q2 = 281 / (281+469) = 0.375

Frequency of S = (0.375)1/2 = 0.612

Frequency of F = p = 1 - q = 1 - 0.612 = 0.388

Frequency of FS = 469 / (281+469) = 0.625

Answer b: Genotype frequencies in the next generation: SS = 0.5; FS = 0.5 (As explained below)

Allele frequencies in the next generation: S = 0.707; F = 0.293 (As explained below)

So, next generation would have 50% of SS and 50% of SF genotype. i.e. 1000 of each type (since we ar given that the next generation has 2000 individuals in it)

Frequency of SS = q2 = 1000 / 2000 = 0.5

So, Frequency of S = q = (0.5)1/2 = 0.707

Frequency of F = p = 1 - q = 1 - 0.707 = 0.293

Frequency of FS = 1000 / 2000 = 0.5

Answer c: Genotype frequencies after the measles epidemic: SS = 0.67; FS = 0.33 (As explained below)

Allele frequencies after the measles epidemic: S = 0.818; F = 0.182 (As explained below)

Frequency of SS = q2 = 1000 / 1500 = 0.67

Frequency of S = (0.5)1/2 = 0.818

Frequency of F = p = 1 - q = 1 - 0.818 = 0.182

Frequency of FS = 500 / 1500 = 0.33

FF FS SS Fitness 0 0.5 1 Survival Rate 0 50% 100% Genotype before epidemic 781 938 281 Genotype after epidemic 0 =938 x 50% = 469 281

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