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In fruit flies, males have the sex chromosomes XY and the females have XX - AQA - A-Level Biology - Question 4 - 2021 - Paper 2
Question 4
In fruit flies, males have the sex chromosomes XY and the females have XX. In fruit flies, a gene for eye colour is carried on the X chromosome. The allele for red e... show full transcript
Worked Solution & Example Answer:In fruit flies, males have the sex chromosomes XY and the females have XX - AQA - A-Level Biology - Question 4 - 2021 - Paper 2
Step 1
All fruit flies are more likely than female fruit flies to have white eyes. Explain why.
Answer
Males have one X chromosome, thus they only need one recessive allele (r) to express the white eye phenotype. In contrast, females have two X chromosomes and need two recessive alleles (rr) to show this trait. Therefore, males are more likely to exhibit white eyes than females.
Step 2
Step 3
Explain the results in Table 2.
Answer
The results in Table 2 demonstrate that the genes for body color and wing development are linked. Given that there are more offspring with grey bodies and long wings (223) than those with black bodies and short wings (218), it suggests limited recombination of these genes during meiosis, hence more parental phenotypes are produced.
Step 4
Calculate how many female fruit flies would be produced from this population in the fifth generation.
Answer
For each generation, each female produces 400 offspring.
- Generation 1: 50 females × 400 = 20,000 offspring.
- Generation 2: 20,000 × 400 = 8,000,000 offspring.
- Generation 3: 8,000,000 × 400 = 3,200,000,000 offspring.
- Generation 4: 3,200,000,000 × 400 = 1,280,000,000,000 offspring.
- Generation 5: 1,280,000,000,000 × 400 = 512,000,000,000,000 offspring.
In standard form, the answer is 5.12 × 10^14.