Review of Natural Selection Types

1. Review of Natural Selection Types

2. Effects of Selection See Fig. 23.12 Coat color

3. Effects of Selection Directional selection consistently favors phenotypes at one extreme See Fig. 23.12 Coat color Coat color

4. Effects of Selection Stabilizing selection favorsintermediate phenotypes See Fig. 23.12 Coat color Coat color

5. Effects of Selection Diversifying (disruptive) selection simultaneously favors both phenotypic extremes See Fig. 23.12 Coat color Coat color

6. Effects of Selection Directional, diversifying (disruptive), and stabilizing selection See Fig. 23.12 Coat color Coat color Coat color Coat color

7. Population Geneticsand the Hardy-Weinberg Equation

8. Population Genetics • In the early 1900s these two men discovered how the frequency of a trait’s alleles in a population could be described mathematically. G H Hardy – British Mathematician Wilhelm Weinberg – German Doctor

9. Population Genetics • For every phenotype how many alleles do you have??? • 2 • 1 from Mom and 1 from Dad • These scientists figured out an equation that can be used to figure out the percentages of alleles and genotypes that are in a population.

10. Population Genetics • In order for their equation to work the population has to be in genetic EQUILIBRIUM • There is no change in the gene pool = no evolution

11. Genetic Equilibrium • 1.) Population size is large • 2.) No gene flow in the population • No new organisms introducing more alleles • 3.) No mutations • 4.) No environmental factors causing natural selection • No trait is favorable over another • 5.) Random mating must occur

12. The Hardy-Weinberg Equation • p2 + 2pq + q2 = 1 • p2 = frequency of the homozygous dominant genotype • 2pq = frequency of the heterozygous genotype • q2 = frequency of the homozygous recessive genotype

13. Hardy-Weinberg • p – frequency of the dominant allele • q – frequency of the recessive allele • Because there are only 2 alleles, the frequency of the dominant allele (p) and the frequency of the recessive allele (q) will add up to 1 or 100% • p + q = 1

14. Hardy-Weinberg Example • In a population of 100 people 28 of them were found to have freckles and 72 were not. We learned in class during our genetics unit that having freckles is a recessive trait and not having them is because of a dominant trait. If this population is in genetic equilibrium then solve for the allelic frequencies and the variables in the hardy-weinberg equation:

15. Genetic Drift

16. Genetic Drift Genetic Drift occurs when the frequency of alleles change due to RANDOM PROCESSES! (NOT natural selection)

17. Bottleneck Effect

18. Bottleneck Effect

19. Founder Effect

20. Queens full of Jacks! • Let’s Mate! • red card=dominant allele=R • black card=recessive allele=r

21. P2 + 2pq + q2

22. Predicted vs Actual • If this population is in equilibrium, we should have the predicted % for our genotypes… • We have…20 rr envelopes and 30RR envelopes • Are we in equilibrium?

23. What should happen? If we are evolving… If we are not…