1. Reproduction leads to genetic drift
• Fisher-Wright process: binomial sampling with replacement in population of size N
• Allele frequency  p (x=n/N in alternative notation) undergoes "diffusion" with   D(p)=p(1-p)/4N
  • Questions relevant to fixation: splitting probability, mean times to fixation or loss, ...
2. Mutations:
• Responsible for maintaining diversity
• For a particular SNP can measure the allele frequency f(p)
• For human population [N~1,000-100,000] with \mu~10^{-9} expect N\mu << 1
3. Selection:
• Acting on phenotypes, it pushes the distribution towards fitter values <\Delta p>=p(1-p)/2 *(d ln[w(p)]/dp)
4. Fitness
• Fitness dependent reproduction
• Increase in mean-fitness, and Fisher's fundamental theorem of natural selection
• 1 allele in a diploid population:
  • Diploid fitness assignments w_{11}=1, w_{12}=1-hs, w_{22}=1-s
  • Wright's equation
• Selection/dominance and fitness landscapes
  • h=0 (A_1 dominant) h=1 (A_2 dominant), 0<h<1 (incomplete dominance), h>1 (disruptive dominance), h<0 (heterozygous advantage)
5. Selection/mutation balance
   • Load of rare mutations (at single locus) on mean fitness of population: w(q_{ss}~1-2\mu is independent of selection factor s!
   • Assuming that the effects of additional loci are multiplicative, genome wide (damaging) mutation rate of W~e^{-2\sum_i\mu_i}
   • This appears to result in a very high rate of genetic death of close to 98%
   • Muller's ratchet and population melt-down counteracted by sexual recombination [Sex and U]
6. Explanatory websites (from past 8.592 projects)
   • Forces of Evolution  by Jing Wang
   • Genetic Drift, Mutation, Selection  by Deng Pan

(MK lecture notes)