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← Theoretical 1

Q39 — Mutation Rates — Asexual vs. Sexual Yeast Populations

Theoretical 1 Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Molecular Evolution & Neutral Theory

To understand the molecular mechanisms behind the origins of adaptation during asexual and sexual reproduction, scientists studied mutations in asexually and sexually replicating populations of the yeast Saccharomyces cerevisiae (100,000 individuals, ~1000 generations). Mutations were classified as intergenic, synonymous, or non-synonymous, and tracked as either “All” (all mutations arising during the experiment) or “Fixed” (mutations present in all individuals by the end).

Figure showing counts of intergenic, synonymous, and nonsynonymous mutations, split by All vs Fixed and by asexual vs sexual yeast populations. Mutations in asexual and sexual populations of the yeast Saccharomyces cerevisiae, broken down by mutation type (intergenic/synonymous/nonsynonymous) and by All vs. Fixed.

Using the information and analysis, determine whether the following statements are true or false:

A. The process of mutagenesis is different in asexual and sexual populations.
B. Synonymous mutations are usually neutral and do not get fixed in sexual populations.
C. The proportion of different mutation types recorded in asexual and sexual populations varies.
D. Due to sexual reproduction, only some useful mutations are fixed in individuals, while in asexual populations their entire 'genetic background' is recorded.
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Question reproduced from IBO 2022, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)