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← Theoretical A

Q22 — ADH1B Allele Geography and Ethanol Metabolism

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

During the first step of ethanol metabolism in humans, alcohol dehydrogenase (ADH) converts ethanol to toxic acetaldehyde that can accumulate in the body.

ADH1B gene of alcohol dehydrogenase has 2 alleles with varying levels of enzyme activity: ADH1B2 is associated with rapid alcohol metabolism compared to ADH1B1. The ADH1B*2 distribution has a distinct geographical pattern (see Figure 1B).

World map showing three historical centers of agriculture (Areas 1-3) and a contour plot of ADH1B*2 allele frequency, with red triangles marking data-collection points. Figure 1. A The historical origins (Areas 1-3) of agriculture emerged 10,000 years BP (“before present”). B Global contour plot of the ADH1B2 allele frequency. The red triangles on the map are points of the data collection.*

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

A. The ancestral allele of the ADH1B gene evolved to degrade high amounts of exogenous alcohol.
B. ADH1B*2 is likely protective against sustained ethanol abuse.
C. Agriculture in Area 3 has been strongly associated with ethanol production.
D. Based on the given data, it is more plausible that positive selection on the ADH1B locus occurred independently in Areas 1 and 2 than negative selection occurred elsewhere.
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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)