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In fruit flies, a gene for body colour has a dominant allele for grey body, G, and a recessive allele for black body, g - AQA - A-Level Biology - Question 6 - 2019 - Paper 2
Question 6
In fruit flies, a gene for body colour has a dominant allele for grey body, G, and a recessive allele for black body, g. A gene for eye colour has a dominant allele ... show full transcript
Worked Solution & Example Answer:In fruit flies, a gene for body colour has a dominant allele for grey body, G, and a recessive allele for black body, g - AQA - A-Level Biology - Question 6 - 2019 - Paper 2
Step 2
6.2 Give one piece of evidence from Figure 4 to show that the allele for grey body colour is dominant.
Answer
If we observe flies 3 and 4, both produced offspring that included black body flies, indicating that the grey body (G) is indeed dominant because it manifests in the phenotype of the offspring.
Step 3
6.3 Explain one piece of evidence from Figure 4 to show that the gene for body colour is not on the X chromosome.
Answer
In Figure 4, Fly 3 produced a black-bodied offspring (Fly 9) when crossed with another grey-bodied fly (Fly 4). Since the black body trait appears in males as well as females, which receive their X chromosomes from their mothers, this evidence supports that the body colour gene is autosomal and not linked to the X chromosome.
Step 4
6.4 A heterozygous grey-bodied, white-eyed female fly was crossed with a black-bodied, red-eyed male fly.
Answer
Phenotypes of parents: Grey-bodied, white-eyed female x Black-bodied, red-eyed male.
Genotypes of parents: GgXr x ggRR.
Genotypes of offspring: GgRr, Ggrr, ggRr, ggrr.
Phenotypes of offspring: Grey-bodied, red-eyed; Grey-bodied, white-eyed; Black-bodied, red-eyed; Black-bodied, white-eyed.
Ratio of phenotypes: 1:1:1:1.
Step 5
6.5 A population of fruit flies contained 64% grey-bodied flies. Use the Hardy-Weinberg equation to calculate the percentage of flies heterozygous for gene G.
Answer
Using the Hardy-Weinberg equation, we have: p^2 + 2pq + q^2 = 1. Given that 64% (p^2) is grey-bodied, p = √0.64 = 0.8. Therefore, q = 1 - p = 0.2. The percentage of heterozygous flies is 2pq = 2(0.8)(0.2) = 0.32 or 32%.