BIOB51H3 Lecture Notes - Lecture 14: Allele Frequency, Genotype Frequency, Heterozygote Advantage
9 Sep 2016
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Biob51 lec 14 migration, non-random mating & drift. Banded and unbanded water snakes p. 237-239 (not box 7. 1) Migration can reduce adaptation to local conditions. 1 gene with 2 alleles: dominant: banded, recessive: unbanded. Mainland: banded = higher fitness (hide from predators: most snakes are banded. Migrants from mainland continually introduce banded allele into island population: data: about 13 snakes per year move to islands, which have about ~1300 snakes. Larger population on mainland = any migrants from island have small effect on mainland allele frequencies. Stickleback ecotypes: morphological divergence based on habitat (inlet stream vs. lake) Hypothesis: divergence between lake-stream populations is constrained by gene-flow (migration) Prediction: negative relationship between adaptive divergence and gene-flow. Adaptive divergence in body size decreases with increased gene flow. Possible explanations (alternative hypotheses): heterozygote advantage, deleterious recessive alleles are not exposed to selection when heterozygous (very slow rate of loss, mutation may re-introduce these alleles (mutation-selection balance)
