Microevolution

1. Microevolution

2. What is the smallest unit that can evolve? • Individual • Species • Genus • Population Do you remember how evolution can be measured? Measure the allele frequency in the gene pool Final Answer? d!

3. Calculating Allele Frequencies Phenotypes for flower color (R = red, r = white) 320 RR 160 Rr 20 rr Total alleles in gene pool: 1000 160 “R” and 160 “r” 40 “r” 640 “R” Number of alleles: Allele frequencies: FR = 800/1000 = .8 Fr = 200/1000 = .2

4. To measure evolution, calculate the allele frequency before and after a given amount of time. If the frequency is the same or constant  no evolution has taken place A non-evolving population is said to be in “Hardy-Weinberg Equilibrium”

5. Hardy-Weinberg (HW) Equations Let’s revisit the previous example involving flower color…. Let p = allele frequency of dominant allele (R) Let q = allele frequency of recessive allele (r) Then… √ .8 + .2 = 1 p + q = 1 HW Equation # 1

6. Hardy-Weinberg (HW) Equations If p = allele frequency of dominant allele (R), then p2 = frequency of homozygous genotype (RR) If q = allele frequency of recessive allele (r), then q2 = frequency of homozygous genotype (rr) If you complete the square, then the frequency of heterozygous genotype Rr must be 2pq So… p2 + 2pq + q2 = 1 HW Equation # 2 √ .64 + .32 + .04 = 1

7. 5 Assumptions for HW equilibrium • Large Population Size • No Migration • No Mutation • Random Mating • No Natural Selection If all 5 conditions are met, no evolution will occur Any deviation results in microevolution of the population

8. What is microevolution? A generation to generation change in a population’s allele frequency

9. What causes microevolution? 5 opposing conditions to HW equilibrium • Genetic Drift • Gene Flow • Mutation • Non-random mating • Natural Selection

10. Genetic Drift In a small population, some individuals may, just by chance, leave behind a few more descendents (and genes, of course!) than other individuals. Genetic Drift always reduces diversity

11. 2 Examples of Genetic Drift • Population Bottleneck • A natural disaster or event causes a population’s size to be greatly reduced Event that causes the population to be reduced in size Final population (not diverse) Initial Diverse Population

12. Over-poaching has bottlenecked the cheetah population, which is now susceptible to random changes in gene frequencies Reduction in diversity and inbreeding puts this species at risk of extinction

13. 2 Examples of Genetic Drift • Founder Effect • Changes in gene frequencies that usually accompany starting a new population from a small number of individuals. Return to Causes of Microevolution

14. Gene Flow • Individuals from one group move into another group. • Makes certain genes more frequent in the population. gene flow Return to Causes of Microevolution

15. Mutation • A change in a DNA sequence • usually occurring because of errors in replication or repair. • Mutation is the ultimate source of genetic variation. Return to Causes of Microevolution

16. Non-Random Mating Individuals choose mates based on preferences for particular traits 2 examples 1) Sexual Selection – mates are chosen based upon behavior/appearance 2) Inbreeding – the choice to mate with related individuals Female peacocks choose mates based upon the male’s plumage display Return to Causes of Microevolution

17. Natural Selection Increases or decreases in allele frequencies due to environmental impact Natural Selection can act upon a population in a variety of ways… Strength of Selection Diversifying Selection = environmental conditions are varied such that individuals at both extremes are favored Directional Selection = favors traits that are at one extreme of a range of traits Stabilizing Selection = selection that acts against extreme phenotypes and favors intermediates