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← Theoretical A

Q23 — Drosophila Allele Frequency Experiment and Stabilizing Selection

Theoretical A Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Natural Selection: Modes & Fitness Population Genetics & Hardy-Weinberg Equilibrium

Aizhan studies polymorphism of locus JR_189021 in Drosophila melanogaster that has only two alleles — A1 and A2. To study the fitness of genotypes, she runs a long-term evolution experiment with ten independent populations of 1,000 flies for 150 generations and measures the frequency of allele A1 in each generation (Figure 1). After completing it, she decided to change the population size and run an experiment using the same setup (Experiment #2). Additionally, she estimated the expected theoretical fit using the fitness values of each genotype reported in the literature. The locus is not under frequency-dependent selection. Assume that homozygous phenotypes are at the extreme of phenotypic distribution. Allele and genotype frequencies within a given generation can be assumed to follow Hardy-Weinberg equilibrium.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. In the long term, the locus is under the directional selection.
B. For experiment #2, Aizhan increased the population size.
C. Flies with the A1A2 genotype have the highest fitness.
D. Flies with the A1A1 genotype have higher fitness than flies with the A2A2 genotype.
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Question reproduced from IBO 2024, Theoretical Exam Part A, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)