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← Theoretical A

Q21 — Out-of-Africa Human Genetic Diversity and Effective Population Size

Theoretical A Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Genetic Drift, Gene Flow & Mutation Human Evolution & Hominid Phylogeny

The ‘Out of Africa’ theory postulates that modern humans originated in Africa and subsequently migrated to different parts of the world. Indeed, large-scale analyses of human genomes strongly support this theory. An example of such support can be observed in the pronounced negative correlation between population genetic diversity and distance from East Africa (Figure 1). Effective population size refers to the size of an idealized population with the same genetic diversity as in the observed population, as if all present genetic diversity within the observed population has been concentrated in a more limited number of individuals.

Scatter plot of mean heterozygosity in human populations against distance from East Africa in kilometers, showing a strong negative correlation (r = -0.91), with African populations at high heterozygosity/low distance and American populations at low heterozygosity/high distance. Figure 1. Average heterozygosity in humans vs distance from East Africa.

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

A. Populations further away from East Africa have larger long-term average effective population sizes.
B. A slightly deleterious mutation is less likely to get fixed (frequency = 1) in the African population compared to the native American population.
C. The reduced genetic diversity in non-African populations is likely due to the founder effect.
D. Figure 1 could represent the heterozygosity of DNA polymerase genes.
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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)