For natural selection to work – traits must vary Individuals & pop’ns do vary extensively

1. For natural selection to work – traits must vary • Individuals & pop’ns do vary extensively • Beaks of G. fortis • Color spots on guppies • Existing variation of pop’n is subject to selection • Individuals live or die based on trait and environmental challenge • Adaptations may develop in pop’n • New species can evolve

2. Phenotypic variation in a population: • Appearance of trait = environment + allele combinations • For evolution to occur, variation in a trait must be partly genetic (nature rather than just nurture) • We can test the contribution of nature and nurture to a given trait. • Breeding animals and following offspring over time • Identical twin studies in humans • Common garden experiments in plants

3. Simple traits vs. continuous traits • Simple traits = one gene with 2 alleles • If dominance, how many possible phenotypes? • Continuous traits (review pgs. 120-121) > 1 gene and many alleles determine the trait How many possible phenotypes? LOTS! • Most traits are continuous • Pop’n of individuals depicted as a hump – many intermediates, few extremes

4. Nat’l selection shapes existing variation in pop’ns • Individuals are selected, but populations evolve • What is a population? • Group of individuals belonging to the same species • Gene pool = collection of alleles • Evolution happens when allele frequencies change over time

5. Ways to change allele frequencies & cause evolution: • Natural selection (and sexual selection) • Limit exchange of genes between populations (i.e. limit gene flow); may result in: a. Each separate pop’n may diverge over time, esp if reinforced by environmental differences (nat’l selex reinforces pop’n differences) b. Non-random mating may reinforce differences within pop’ns:

6. Gene flow - tends to reduce genetic differences between populations Could have a + or - effect on overall fitness, depending on the situation

7. Inbreeding can occur in small populations. Small populations are formed in two ways: 2b. Inbreeding is one form of non-random mating • Founder effect Bottleneck

8. Ways to change allele frequencies & cause evolution: 3. Random change b/c pop’n is small (genetic drift)

9. Ways to change allele frequencies & cause evolution: 4. Mutation to DNA (deleted or duplicated base makes different protein) • Only source of new alleles of genes, introduces new variation • Mutations are random – can be bad, neutral or good • Non-lethal mutations are source of new, potentially beneficial proteins that can be selected for • Mutations caused by environment are relatively common; but random • Human mutation rate ~ 10-8 (1 in 100 million) per nucleotide per generation, Average person has 1.6 new alleles created by mutation, and new combinations are created by crossing-over and independent assortment, bacteria 10-5 to 10-7 per gene per generation • where it happens in genome is random • Mutation must be present in gametes to be inherited • Small mutations can produce enormous change in body plan and form Hox genes Evo Devo Chimps and humans genetically differ by 1-2%, can developmental switches generate different appearance?

10. Microevolution – change over short time and within same species. • Directional selection (1) • Stabilizing (balancing) selection (2) • Disruptive (diversifying) selection (3) • Macroevolution – large-scale changes that occur over a long time within a lineage • Speciation – new species arise. How? • Reproductive isolation must occur • Reproductive isolating mechanisms: genetic isolation (4), habitat isolation (5), behavioral isolation (6), temporal isolation (7), mechanical isolation (8), reduced hybrid fertility (9)