Adaptive geographic differentiation restricted gene

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Adaptive geographic differentiation Restricted gene flow (migration) Non-adaptive differentiation due to genetic drift Some traits (and alleles) are more common in one set of subpopulations than in others Allopatric populations Parapatric populations Partially sympatric populations 26
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Geographic variation Parapatric variation in rat snake color morphs Hybrid zone at morph range boundaries Not all traits (or loci) may separate by geography in the same pattern 27 Rat snake mtDNA gen eal ogy does not match color pattern differences across its range
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Geographic variation Cline = gradual change in trait over distance Fraction “Slow” form of Adh 28
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Geographic variation: genes and environment Variation between ecotypes due to genetics Coastal Mid-altitude Alpine 29 Variation within an ecotype due to environment Clausen et al.
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Geographic differentiation What fraction of all genetic variation in the species is due to differences between populations? Compared to within-population variation? Are some loci or traits more differentiated than the genome-wide average? Local adaptation? 30
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Allison’s 2004 Perspective in Genetics Historical account of human sickle-cell disease research Mostly in Africa Simple genetic basis to malarial immunity Two red blood cell phenotypes Two main hemoglobin assay phenotypes HbA & HbS HbS dominant to HbA wrt presence of sickled cells AA homozygotes most common SS homozygotes highly detrimental AS heterozygotes beneficial for children infected with Plasmodium Allison 1954 0% 20% 40% 60% 80% 100% sicklers non-sicklers with parasitaemia without parasitaemia 27.9% 72.1% 45.7% 53.3% 31 Percent of patients
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Allison’s 2004 Perspective in Genetics Geographic distribution of Plasmodium and AS genotypes highly correlated 32
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Allison’s 2004 Perspective in Genetics World-wide, many HbS haplotypes Independent evolution of HbS (4 African + 1 south Asia) Same causal protein difference (glutamic acid G A G valine G T G) Haplotype = unique combination of variant sites Lapoumeroulie et al. 1992 HbA haplotype HbS haplotypes GCTTC77CA ..... 85.. ..G..84T. AG..T84.C .G.C.69.. .G.C.95.. 33 A T T T T T
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Next class: Genetic drift 34
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