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 for red eyes, R, and a recessive allele for white eyes, r, and is located on the X chromosome. Figure 4 shows the phenotypes of fruit flies over four generations. **Figure 4** 1 --- 2 Grey body Black body | 3 --- 4 Grey body Grey body | 5 --- 6 Grey body Black body | 7 --- 8 Grey body Black body | 9 --- 10 Grey body Grey body | 11 --- 12 Grey body Black body | 13 Black body 6.1 Give the full genotype of the fly numbered 6 in Figure 4. Genotype = 6.2 Give one piece of evidence from Figure 4 to show that the allele for grey body colour is dominant. 6.3 Explain one piece of evidence from Figure 4 to show that the gene for body colour is not on the X chromosome. 6.4 A heterozygous grey-bodied, white-eyed female fly was crossed with a black-bodied, red-eyed male fly. Complete the genetic diagram below to show all the possible genotypes and the ratio of phenotypes expected in the offspring from this cross. Phenotypes of parents: Grey-bodied, white female × Black-bodied, red-eyed male Genotypes of parents: ______________ × ______________ Genotypes of offspring: Phenotypes of offspring: ______________ Ratio of phenotypes: 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.

A-Level AQA Biology 7.1 Inheritance (A Level only): In fruit flies, a gene for body

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 1

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 1

Step 1

Give the full genotype of the fly numbered 6 in Figure 4.

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Answer

The full genotype of the fly numbered 6 in Figure 4 is GgXRY.

Step 2

Give one piece of evidence from Figure 4 to show that the allele for grey body colour is dominant.

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Answer

From Figure 4, it can be observed that flies 3 and 4, which are grey-bodied, produced offspring (fly 6) with black-bodied phenotype only when paired with the black-bodied fly. This demonstrates that the grey body allele (G) is dominant over the black body allele (g).

Step 3

Explain one piece of evidence from Figure 4 to show that the gene for body colour is not on the X chromosome.

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Answer

In Figure 4, both male and female flies can have grey bodies, as evidenced by flies 1, 2, and 3. If the body colour gene were on the X chromosome, males would not exhibit the recessive trait (black body) as homozygous. Since males can be grey-bodied, it indicates that the gene is autosomal, not linked to the X chromosome.

Step 4

Complete the genetic diagram below to show all the possible genotypes and the ratio of phenotypes expected in the offspring from this cross.

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Answer

Genotypes of parents: GgXr × ggXY

Genotypes of offspring: 1 GgXRY (Grey-bodied, red-eyed) 1 GgXrY (Grey-bodied, white-eyed) 1 GgXRY (Grey-bodied, red-eyed) 1 ggXRY (Black-bodied, red-eyed) 1 ggXrY (Black-bodied, white-eyed)

Phenotypes of offspring:

3 Grey-bodied (1 GgXRY + 1 GgXrY)
2 Black-bodied (1 ggXRY + 1 ggXrY)

Ratio of phenotypes: Grey-bodied : Black-bodied = 3:2.

Step 5

Use the Hardy–Weinberg equation to calculate the percentage of flies heterozygous for gene G.

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Answer

Given that 64% (or 0.64) of the flies are grey-bodied, we can denote the frequency of the dominant allele (p) as follows:

Using the equation: $p^2 + 2pq + q^2 = 1$

Where:

$p^2$ = frequency of homozygous grey-bodied (G)
$2pq$ = frequency of heterozygous (Gg)
$q^2$ = frequency of homozygous black-bodied (gg)

Let’s set $q^2 = 0.36$ (since 1 - 0.64 = 0.36):

Now, taking the square root gives us: $q = rac{1}{q} = rac{0.6}{1}$

Then, $p = 1 - q = 0.4$ .

Finally, to find the heterozygous genotype ( hence, $2pq = 2(0.4)(0.6) = 0.48$ ) which shows that 48% of the flies are expected to be heterozygous for gene G.

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 1

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 1

Give the full genotype of the fly numbered 6 in Figure 4.

Give one piece of evidence from Figure 4 to show that the allele for grey body colour is dominant.

Explain one piece of evidence from Figure 4 to show that the gene for body colour is not on the X chromosome.

Complete the genetic diagram below to show all the possible genotypes and the ratio of phenotypes expected in the offspring from this cross.

Use the Hardy–Weinberg equation to calculate the percentage of flies heterozygous for gene G.

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