Pop Size Matters

• Genetic Drift
  • It is basically random sampling of alleles in the subsequent generation
  • Using a mathematical model, it has been show that an average of 4N generations (N = population size) are required for an allele to get fixed in that population
  • Infinite Mutaion model (measure of increase of allels) and Stepwise mutation model (in/decrease of alleles in a pop),. often used to measure the loss of allles (Drift) in a population
• Importance of linkage
  • Linkage plays an impo role. Deleterious genes are selected in linked status, while lost in unlinked status
• Genetic Draft
  • Reduced efficiency of selection on a linked loci=> Hill-Robertson Effect
  • Selective sweep (or hitchhiking effect) is the reduction or elimination of variation among the nucleotides in neighbouring DNA of a mutation as the result of recent and strong natural selection.
  • Effective population size: is the inbreeding effective pop size
  • Relationship between effective and actual size: They are proportional, but effective pop size gets reduced with more of selective sweeps
• Population size:
  • Pop size inversely proportionate to to the body size
• Higher Mutation rates:
  • Genome size is +vely correlated with the base-substitution rate
  • Genome size is -vely correlated with the recombination rate
• Effective pop size:
  • Within species allelic diversity (basically the subtitutions per silent site) is more in prokaryotes (more pop size and less genome size) compared to vertibrates
• Sources of Bias:
  • Nucleotide heterozygosity
  • Mutation
  • Mismatch repair mechanisms
• Resolution of Paradox variation
  • EPS vary between larger and smallest organisms atleast to 5 order
• Mutationas a Weak selective force
  • Alleles of more complexity will be more suceptible to mutation
• Genome size is inversely correlated with silent site mutation

Category:Readings