Ch 16 Evolution of populations

1. Ch 16Evolution of populations

2. Crash Course: Population Genetics • https://www.youtube.com/watch?v=WhFKPaRnTdQ

3. 16-1 Genetic equilibrium • Population genetics: study of evolution from a genetic point of view • Basically how populations of a species evolve • But what is a population? • Group of members of the same species living in the same area

4. Sources of genetic variation • Three main sources • Mutations: any change in sequence of DNA • Replication mistakes • Radiation/environmental causes • recombination: reshuffling of genes • Random pairing of gametes

5. Bell curve • Many traits in nature show trends like this Phenotype continuum # of individuals with that trait

6. Number of phenotypes produced depends on how many genes control that trait • Single gene traits- have two alleles • Two distinct phenotypes

7. Polygenic traits- controlled by two or more genes • Results in multiple phenotypes

8. Gene pool- all genes, including all different alleles, that are present in a population • frequency (of an allele)- number of times alleles occur in a gene pool • Percentage • Genetic definition of evolution? • Change in relative frequency of alleles in a population over time

9. Phenotype frequency • How often a specific phenotype is observed in a population • Can be written mathematically • Frequency = # indiv. w/a particular phenotype total # of indiv. in population

10. Hardy-Weinberg equilibrium • When evolution is not occurring • Allele frequencies remain the same • In order for evolution to not occur, certain conditions must be met.

11. Evolution Versus Genetic Equilibrium • Hardy-Weinberg principle = Genetic Equilibrium • Random Mating – Equal opportunity to produce offspring • Large Population – Genetic Drift does not effect Allele Frequency • No Movement into or out of Population – The gene pool must be kept together (no new alleles) • No Mutations – Mutations cause new forms of alleles changing the frequency • No Natural Selection – All genotypes must have equal probability of surviving.

12. Hardy-Weinberg equilibrium Allele frequency equation p + q = 1 • p = frequency of dominant allele • q = frequency of recessive allele Together, they make 100% of alleles for a gene in that population • If p = 34%, what is q? • If q = 19%, what is p? 0.66 0.81

13. Hardy-Weinberg equilibrium • Genotypic frequency equation p2 + 2pq + q2 = 1 • p2 = homozygous dominant frequency • 2pq = heterozygous frequency • q2 = homozygous recessive frequency • If p = .46, what is p2? • If p = .12, what is q2? • If q =.31, what is 2pq? 0.2116 0.7744 = 77% 0.4278

14. 16-2 Disruption of genetic equilibrium • Mutation • Occur at a relatively constant rate over time • Can be sped up when exposed to mutagens • Gene flow: process of genes moving from one population to another • Immigration: moving into a population • Emigration: moving out of a population

15. Genetic Drift • Alleles can become rare by chance • Over time a series of chance occurrences can cause an alleles to become common in a population • Effects of genetic drift are more dramatic with small population size • Founder effect: change in allele frequencies as a result of migration of a small subgroup of a population

16. Genetic Drift Section 16-2 Sample of Original Population Descendants Founding Population A Founding Population B

17. Genetic Drift Section 16-2 Sample of Original Population Descendants Founding Population A Founding Population B

18. Genetic Drift Section 16-2 Sample of Original Population Descendants Founding Population A Founding Population B

19. Nonrandom mating • Sexual selection: tendency of individuals to choose a mate with certain traits. • Common in birds • Peacock display • Tropical birds of paradise - Papua New Guinea • The amazing Lyrebird - Australia

20. Natural selection • Natural selection on a single gene traits can lead to changes in allele frequencies • Natural selection on polygenic traits • 3 possible effects • Directional selection • Stabilizing selection • Disruptive selection https://www.youtube.com/watch?v=vCHdT9MWIaA

21. Directional selection • When individuals at one end of curve have higher fitness than individuals in the middle or the other end

22. Stabilizing selection • When individuals near the middle have higher fitness than the individuals at either end

23. Disruptive selection • When individuals at upper and lower ends have higher fitness than individuals near the middle

24. 16-3 Formation of Species • As new species evolve, populations become reproductively isolated from each other • Reproductive isolation: when two members of populations cannot interbreed and produce fertile offspring • Separate gene pools

25. Isolation Mechanisms Geographic Isolation: - separation of animals in a specific region - formation of river, canyon, mountain

26. Isolation Mechanisms Behavioral Isolation: - differences in courtship or reproductive behaviors -meadowlark songs • Temporal isolation: • -two or more species reproduce at different times • -orchids

27. Formation of species • Allopatric speciation: when species arise from geographic isolation • Different places https://www.youtube.com/watch?v=cSgulsydsQU

28. Reproductive isolation • Prezygotic isolation: premating isolation • Species may live • in different places • Reproduce at different times • Have different mating behaviors • Postzygotic isolation: postmating isolation • Hybrids may be weak • Hybrids may be sterile

31. Sympatric speciation • Sympatric speciation: when two subpopulations become isolated while living in the same area

32. Rates of speciation • Gradualism: speciation at gradual and regular rate

33. Punctuated equilibrium: periods of sudden, rapid change followed by periods of littelchange