Consider two populations of guppies living in a tropical stream. One is upstream

Question

Consider two populations of guppies living in a tropical stream. One is upstream of a waterfall, and the other is downstream. In both populations, homozygous individuals have either blue or red stripes, depending on the allele they carry: R for the red allele and B for the blue. RB heterozygotes have purple stripes. In the downstream population only, there are crayfish that feed on the guppies. Because the crayfish can't see red colors, the red-striped guppies have higher fitness than blue or purple. Comparison to the upstream population, where there are no crayfish, indicates that the selection coefficient on purple and blue guppies is 0.25. The current frequency of the R allele is 0.64. Your job is to calculate the percent change in allele frequency that occurs in the next generation due to crayfish predation. To do this you should: a) Use the Hardy-Weinberg principle to determine expected genotype frequencies in the generation without selection b) Determine the relative fitness of each genotype c) Calculate the genotype frequencies in the new population following selection d) Find the percent change in allele frequency of the resistant R allele.

Explanation / Answer

a)The formula for expected genotype frequency q=1-p

Where p is the initially present genotype and q is the newly expected one.

q=1-0.64 (0.64 is the current frequency)

q=0.36

b)The relative fitness of each genotype can be given in comparison mode:-

Red stripped guppies-high fitness level

Blue stripped guppies-medium fitness level

Purple stripped guppies-very low fitness level

c)The genotype frequencies in new population selection is already calculated in question 'a'.

The new frequency of genotype=0.36

d)The percent change in allele frequency of resistant R allele is calculated as follows:-

New frequency from previous answer=0.36

Percent change=0.36×100=36%

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.