1. EVOLUTION: GENES AND POPULATIONS CH 23 http://evolution.berkeley.edu/evoli brary/news/070401_lactose

2. Organisms DO NOT evolve. Natural selection acts on individuals causing populations to evolve

3. Microevolution: changes in allele frequencies over time. Caused by: – Natural selection – Genetic drift – Gene flow Only natural selection causes adaptive evolution

4. I. Genetic Variation and Evolution In order for evolution to occur, there must be genetic variation in a population

5. A. Where does genetic variation come from? New genes and alleles come from mutation and gene duplication Gene recombination during meiosis: reshuffles alleles during sexual reproduction Mutation is most important in asexually reproducing organisms while gene recombinations are more important in sexually reproducing organisms

6. B. Hardy Weinberg Equilibrium and Allele Frequencies 1. The Hardy Weinberg theorem Population: a group of actively interbreeding members of a species Gene pool: all of the alleles present in a population

7. The Hardy-Weinberg theorem states that allele frequencies in a population will remain unaltered from generation to generation IF the following criteria are met: – Extremely large population – No mutation – No selection – No gene flow (migration) – Mating is random

8. The Hardy Weinberg theorem describes a hypothetical non-evolving population In real populations, allele frequencies do change The five criteria for equilibrium are rarely met in nature

10. Ex: 1000 AA 2000 Aa 2000 aa Calculate frequency of A and a

11. 2. Using Hardy Weinberg to calculate allele frequencies p 2 + 2pq +q 2 = 1 p + q =1 p 2 = frequency of homozygous dominants 2pq = frequency of heterozygotes q 2 = frequency of recessives p = frequency of dominant allele q = frequency of recessive allele

12. Ex: Albinism is a recessive disorder and occurs with a frequency of 1/20000 people What is the frequency of individuals who are: – Dominant – Recessive – Heterozygous

13. II. Why Do allele Frequencies Change? Allele frequencies can change due to – mutation – gene flow – genetic drift – natural selection

14. A. Mutation: introduces new alleles

15. B. Gene flow (migration): individuals and their alleles enter and leave the population

16. gene flow can limit variation and reduces speciation – new genes can enter into the population, which may have a negative effect. This lowers survivability

17. mating causes gene flow between central and eastern populations Immigration from mainland introduces alleles that decrease fitness – High immigration between mainland and central region – Low immigration between mainland and eastern region

18. Gene flow can also increase fitness of population Insecticide resistant genes entering a population can increase the fitness of that population

19. C. Genetic drift: in small populations, allele frequencies change RANDOMLY from generation to generation https://highered.mcgraw- hill.com/sites/dl/free/0072 835125/126997/animation 45.html

21. Bottleneck effect: – a drastic change in environment could significantly reduce population size. – New allele frequency may not reflect original population

22. Think of the effect of excessive hunting on animal populations

23. Founder effect: – a few individuals from a population get separated from the rest

24. Genetic drift is: – More significant in small populations and RANDOMLY causes allele frequencies to change – Can reduce variation in a population – Can cause unfavorable alleles to become fixed

25. D. Selection: environment or humans select for favorable alleles which are then passed on.

26. Selection is the only mechanism of adaptive evolution It is the fitness of individuals that affects future generations Fitness is the ability to reproduce and pass on alleles Natural selection acts on organisms’ phenotype which thus favors certain genotypes

27. Types of natural selection: – Selection to match environment

28. – Selection to avoid predators: Camouflage Mimicry Poison

29. – Selection for pesticide resistance

30. – Sexual selection: natural selection for mating Intrasexual selection: members of the same sex compete to mate Intersexual selection: when females choose their mate

31. The three modes of selection

32. Directional selection: – favors individuals at one end of phenotypic range Disruptive selection: – favors individuals at both ends of phenotypic range Stabilizing selection: – acts against extreme phenotypes

33. III. Maintaining Alleles in a population Natural selection tends to remove variation by favoring certain alleles Mechanisms to preserve variation: – Diploidy: Recessive allele is hidden in heterozygote. Explains why Tay Sachs is still around

34. – Heterozygote advantage: in the case of malaria, being heterozygous for sickle cell anemia protects you from malaria and you don’t have sickle cell anemia

35. – Frequency dependent selection: fitness of a phenotype decreases if it becomes too common in the population