Bio1B Evolution 5 Last lecture Predicting genotype freq s Hardy Castle Weinberg Equilibrium Application Predicting heterozygote frequencies for recessive traits Evolutionary processes Sampling effects genetic drift Relevance in evolution loss of variation bottlenecks Mutation as the ultimate source of variation effects on fitness Migration as gene flow Today Evolutionary processes Migration and genetic clines Selection Fitness Forms of selection Heterozygote advantage eg sickle cell anaemia Directional selection eg coat color in mice genome signatures experimental evidence 1 Migration as gene flow Gene flow movement of genes among populations Arises from net movement birth reproduction or gamete dispersal zygotes Spreads new mutations maintains variation Opposes effects of genetic drift or local selection Spread of genes from GMO crops is a concern 2 Genetic fitness Selection acts through the phenotype Fitness Survival and reproduction relative to other phenotypes or genotypes in the population Relative fitness can be environment dependent Sorry Arnie 3 Forms of selection Fig 23 13 4 Example of Heterozygote advantage sickle cell anaemia Relative fitnesses Without malaria HbbAA HbbAS HbbSS anaemia With malaria HbbAS HbbAA HbbSS More resistant to malaria Note fitness of HbbAS depends on 5 environment malaria 6 Association between melanic phenotype and Mc1r allele in rock pocket mice from Pinacates lava flow Hopi Hoekstra in the field 7 Geographic cline Some key genes in melanin production pathway Agouti melanistic mutations Recessive regulatory coding X Mc1r Melanistic mutations Dominant structural So what Mc1r melanoma 8 Experimental evidence for rapid evolution due to selection Eg guppy color field experiments text pp460 Others microbial evolution etc etc Fig 22 13 9 Genomic signatures of recent selection Variable site New mutation arises that increases fitness Under directional selection increases to p 1 drags linked sites with it Results in a region of low variation relative to others Storz 2005 Variation high high low 10 high Genomic signatures of selection localized reductions in diversity What s with my crazy dog Sutter et al 2007 Science 316 112 11
View Full Document
Unlocking...