BIOL 206 Lecture Notes - Lecture 4: Linkage Disequilibrium, Genetic Hitchhiking, Heterozygote Advantage

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25 Aug 2016
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Week 4 (One Lecture, midterm week)
With a finite population, section becomes less effective and less predictable
oA variety of actions can occur with a finite population size:
oAdvantageous alleles may be lost
oDisadvantageous alleles may be fixed, due to small population size
oHeterozygote advantage may decline and may be lost
oNew advantageous alleles may have a “kick-start” and flourish in the new, small population
oDisadvantageous alleles may be lost faster in smaller populations
Nonrandom mating (Inbreeding): Results in a loss of fitness due to reduction in heterozygosity,
and an increase in homozygosity in the population.
oExpression of deleterious recessive alleles
Migration: Can be both advantageous or disadvantageous depending on the situations
oIt can spread advantageous allelic mutations from population to population
oIt can also disrupt local adaptions
Mutations: Ultimately required by selection for adaptations
oFavourable alleles tend to spread throughout the population while unfavourable alleles perish
into extinction
Week 5
Linkage Disequilibrium: Nonrandom association of alleles at two or more loci
Linkage Equilibrium: Random association of alleles at two or more loci
Many ways to cause linkage disequilibrium
oPhysical linkage:
oSelection on multilocus genotypes
oGenetic drift
oPopulation admixture: When two populations with different genotypes come and mix together
Importance:
oAssociative Overdominance: Deleterious alleles are not eliminated easily
Heterozygote advantage due to negative selection at linked loci
oBackground Selection: Decrease in frequency of neutral or positive allele due to negative
selection at linked locus
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