IV. The Process of Evolution

1. IV. The Process of Evolution A. Two types of evolution • Macroevolution – any change of a • species over time into another. Any • changes or “long-term”trends at • higher taxonomic levels (i.e. new • genera, families, phyla) 2. Microevolution – A change in gene frequencies (i.e. alleles) within a pop. or species over time. Ex. Overuse of antibiotics has selected for resistant microbes

2. Example (microevolution):  light v. dark colored moths  frequency due to change in env’t (i.e. color of tree trunk)  industrial melanism

3. B. Causes of microevolution • Natural selection • a. gradualism – species evolve at a slow • and constant pace • b. punctuated equilibrium – species • evolve rapidly over short time then • remain the same for long periods

5. 2. Mutations – a change in an allele  the origin of genetic variation 3.Gene Flow – the mov’t of alleles b/n populations due to migration of breeding indiv.  Results in interbreeding

6. 4. Genetic Drift – allele freq. change due to chance  causes alleles to be lost from pop.  small populations suffer (i.e. greater chance that rare alleles won’t contribute to make-up of next generation) ex. Coin toss: toss 100x: probability is 50/50 of getting heads/tails toss 10x: better chance of getting 8 heads/2 tails

7. Genetic drift can be due to: a. bottleneck effect – dramatic decrease in alleles b/c of major disaster ex. Hunting in 1890’s reduced one elephant seal pop. to ~20 indiv.  very little genetic variation  24 exact same proteins

9. b. Founder’s effect – 1. when a new pop. is started, the pioneers contain only a fraction of the total genetic diversity of original gene pool 2. also not likely to have all representations

10. 5. Nonrandom mating  Examples: a. assortative mating – mate with someone w/ same phenotype (e.g. tall people) b. sexual selection – mates are chosen on basis of particular appearance

11. C. Genetics of evolution (population genetics) • Gene pool – all the various alleles at • every locus of every indiv. in a pop. •  the gene pool is defined by allele • frequencies 2. Calculating gene pool frequencies  the Hardy-Weinburg Principle

12. Hardy- Weinburg Principle • states that the frequencies of alleles and genotypes in a population’s gene pool will remain constant (i.e. unchanging) over generations as long as there is: 1. no selection 2. no mutations 3. no gene flow 4. no genetic drift 5. random mating • If these conditions are met, the pop. is • @ equilibrium

13. So, what is the final result of changes in gene pool allele and genotypic frequencies? V. Speciation – the formation of a new species Due to Isolation – any geographical, reproductive, or behavioral event preventing gene flow b/n populations

14. B. Modes of speciation 1. Allopatric – geographic separation prevents gene flow

15. Example of allopatric speciation • Darwin’s finches (Galapagos Islands)

16. Adaptive Radiation – different species evolved from one common ancestral species

17. 2. Sympatric – reproductive isolation w/o any geographic barrier  results in polyploidy indiv.  common in flowering plants (e.g. sunflowers)  rare in animal (but, orcas)

18. VI. Patterns of Evolution • Divergent – two species gradually • become increasingly different •  occurs when related species diversify • to new habitats •  Example: humans and apes

19. 2. Convergent – When diff. species begin to share traits b/c of shared env’t example: whales (mammals), sharks (fish), penguins (birds)

20. 3. Parallel – when two species evolve independently while maintaining the same level of similarity  occurs b/n unrelated species that don’t occupy the same habitat  example: marsupial v. placental mammals (give birth to live young)

22. 4. Coevolution – Species that interact closely often adapt to one another. Ex. Hawk moth and Orchids