Consider a hypothetical fish whose scale color is controlled by one gene with tw

Question

Consider a hypothetical fish whose scale color is controlled by one gene with two alleles. The gene is inherited in an incomplete dominance pattern. In a wild population of 1000 of these fish, there are 625 with blue scales and genotype SBSB, 175 with green scales and genotype SBSY, and 200 with yellow scales and genotype SYSY.

1. What is the allele frequency of the SB gene and the SY gene?

2. What is the genotype frequency observed in this population for blue fish, for green fish, and for yellow fish?

3. What is the genotype frequency expected if the population follows Hardy Weinburg equilibrium for the blue, the green, and the yellow fish.

4. Explain why this fish population is, or is not in Hardy Weinburg equilibrium. If it is not in Hardy Weinburg equilibrium, what type of selection is likely occurring?

Explanation / Answer

1) p2=625/1000

=0.625

p=0.790

therefore q=1-p (as p+q=1)

               =0.21

allele frequency of SB gene=0.790

allele frequency of SY gene=0.21

2) observed genotypic frequency

for blue fish=625/1000x100=62%

green fish=175/1000x100= 17.5%

yellow fish=200/1000x100= 20%

3) genotype frequency for blue fish (following Hardy-Weinberg equilibrium)

=p2=( 0.79)2 =0.62 (62%)

genotype frequency for green fish=2pq

=2x0.79x0.21=0.33 (33%)

genotype frequency for yellow fish=q2 =(0.21)2 =0.04=(4%)

4) The population is not following Hardy-Weinberg equilibrium, because there is a change in allelic frequencies in the population. Here it is more of a directional selection where the dominant phenotype is preferred compared to the intermediate and the recessive phenotype.

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

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