Question

You are studying a population of wild turtles on a remote Pacific island. You have been following the allelic frequencies at a single two-allele locus 'S', which controls embryonic survival through simple Mendelian inheritance with dominance. The population has been in Hardy-Weinberg equilibrium at this locus for many generations.

At Hardy-Weinberg equilibrium, the frequency of the recessive allele S^d is 0.88

The genotypic frequencies at Hardy-Weinberg equilibrium are as follows:

f(S^DS^D) = 0.0144

f(S^DS^d) = 0.2112

f(S^dS^d) = 0.7744

An increase in ocean temperature between 2018 and 2019 is thought to have driven the population away from Hardy-Weinberg equilibrium at the S locus.

The numbers of sampled offspring by genotype after the 2019 hatch are as follows:

S^DS^D : 200

S^DS^d : 200

S^dS^d : 40

Calculate the relative fitness (W) values for each genotype (you will need all these values in a subsequent step).

a) The relative fitness value for the S^dS^d genotype is [A] (enter your answer as a decimal in the form '0.x'; do not spell out the number as a word; there are no units to include)

b) The type or form of natural selection that has occurred is [B] (use the specific phrase that describes this form of selection completely!).

Now, calculate all genotypic frequencies in the 2019 offspring (first generation after selection):

c) post-selection f(S^DS^D) = [C] (perform this and the following two calculations (d and e) to four significant figures after the decimal point; enter your answers in the exact form '0.wxyz'; make sure to round off correctly; there are no units)

d) post-selection f(S^DS^d) = [D]

e) post-selection f(S^dS^d) = [E]

f) The frequency of the S^d recessive allele in the 2019 offspring (first generation after selection) is [F] (perform the calculation with four significant figures, then round off to 2 significant figures in the final answer; enter your answer in the exact form '0.xy')

Answer 1

The population of wild turtles are in Hardy Weinberg equilibrium and the allele S controls the embryonic survival through simple Mendelian inheritance with dominance. The frequency of recessive allele S^d, therefore, the frequency of dominant allele, S^D, , the given genotype frequencies are as follows: f(S^DS^D)= p²= 0.0144; f(S^DS^d), 2pq=0.2112; f(S^dS^d), q²=0.7744

The number of sampled offspring by genotype after the 2019 hatch are as follows: S^DS^D=200; S^DS^d=200; S^dS^d=40

Therefore, the relative fitness for the S^DS^D genotype, ; relative fitness for the S^DS^d genotype, ; relative fitness for the S^dS^d genotype,

(a) The relative fitness value for the S^dS^d genotype =0.2.

(b) Here, w_DD=w_Dd=1 and w_dd<1. The heterozygote alomg with the homozygous dominant has the highest fitness, which is greater than that of the homozygous recessive. Natural selection is operating against the recessive allele, S^d.

The mean fitness,

(c) Post selection f(S^DS^D)=

(d) Post selection f(S^DS^d)=

(e) Post selection f(S^dS^d)=

(f) Frequency of allele S^D after selection, ; therefore the frequency of the S^d allele after selection, .