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Genetic drift in clines which are maintained by migration and natural selection
Genetics
|September 1, 1975
Summary
Genetic drift causes gene frequency clines to fluctuate. This study quantifies these wobbles in large populations using a stepping-stone model, finding they depend on population size (N) and migration (m).
Area of Science:
- Population Genetics
- Evolutionary Biology
- Quantitative Genetics
Background:
- Gene frequency clines represent gradual changes in allele frequencies across geographic space.
- Genetic drift, random fluctuations in allele frequencies, can impact the stability and shape of these clines.
- Understanding drift's effects is crucial for predicting evolutionary trajectories and population structure.
Purpose of the Study:
- To develop a theoretical framework for quantifying the effects of genetic drift on migration-selection clines.
- To investigate how drift influences cline shape, variation, and spatial correlations in large populations.
- To analyze drift's impact in a stepping-stone model with varying selection landscapes.
Main Methods:
- Development of a linear approximation for cline dynamics in large populations.
- Application of the approximation to a stepping-stone model with single haploid locus.
- Calculation of cline slope, standardized gene frequency variance, and inter-neighbor correlations.
- Comparison with computer simulations for validation.
Main Results:
- Genetic drift causes clines to deviate from their expected positions, with deviations primarily dependent on population size (Ns) and migration rate (Nm).
- Standardized variances and neighbor correlations vary along the cline, especially with smooth selection changes.
- The local behavior of gene frequencies is well-approximated by adaptations of existing stepping-stone models.
- No pathological gene frequency deviations were observed near selective region boundaries.
Conclusions:
- Genetic drift introduces significant 'wobble' into migration-selection clines, predictable by population size and migration parameters.
- The study provides quantitative measures for drift's impact on cline stability and spatial genetic structure.
- Theoretical predictions are broadly supported by simulation, offering insights into evolutionary processes in structured populations.