Molecular evolution What is molecular evolution? Mutation, drift and selection acting at the molecular level

1. Molecular evolution What is molecular evolution? Mutation, drift and selection acting at the molecular level Change in DNA sequences ATGGTCAAGCTTACCATG ATGCTCAAGCTTACCATG ATGGTCAAGCTTACCATG ATGGTCAAGATTACCATG ATGGTCAAGATTACCTTG

2. Molecular evolution • Mutation, drift and selection acting at the molecular level • Mutation – most mutations are base substitutions • Drift – most populations are finite, so drift can have some effect • some new mutations should drift out of population • some new mutations should eventually drift to fixation • Selection – acts on mutations that affect fitness • should act against harmful mutations  elimination • should favor beneficial mutations  fixation substitution – fixation of a new mutation ATGGTCAAGCTTACCATG ATGCTCAAGCTTACCATG ATGGTCAAGCTTACCATG ATGGTCAAGATTACCATG ATGGTCAAGATTACCTTG ATGGTCAAGATTACCATG ATGGTCAAGATTACCATC

3. Neutral Theory of Molecular Evolution remember....

4. Evolutionary biology since the modern synthesis • Revising the modern synthesis • Is evolution always gradual? • Eldredge and Gould, 1972, Punctuated Equilibrium • How important is genetic drift relative to natural selection? • Kimura, 1968, Neutral Theory • Is speciation always slow? • Does speciation only occur in isolated populations? LECTURE 12

5. How genetically variable are populations? H0: little variation LECTURE 15 - because selection should remove less fit alleles - implies: mutations either good or bad, not neutral Ha: lots of variation neutral theory – most mutations are neutral selectionist theory – variation in selection maintains different alleles in population - heterozygote advantage - fluctuating selection (selection varies in time or space) - frequency-dependent selection (rare allele is advantageous)

6. Neutral Theory of Molecular Evolution • most base substitutions are selectively neutral • drift dominates evolution at the molecular level • Under drift, rate of fixation should be steady through time • because drift is the result of chance alone (can happen any time) • predicts steady change through time = “molecular clock” ATGGTCAAGCTTACCATG ATGCTCAAGCTTACCATG ATGGTCAAGCTTACCATG ATGGTCAAGATTACCATG ATGGTCAAGATTACCTTG ATGGTCAAGATTACCATG ATGGTCAAGATTACCATC