Hardy-Weinberg Equilibrium

1. Hardy-Weinberg Equilibrium -And how it affects evolution.

2. Hardy-Weinberg Principle • Predicts how gene frequencies (number of dominant and recessive alleles) will be transmitted from generation to generation. • The genes of a population are known as the gene pool. • The Hardy-Weinberg principle states that there will be no change in allele frequency of a population over time. This is called genetic equilibrium.

3. Hardy-Weinberg Equilibrium • Genetic equilibrium will not change over time- • Frequencies in each successive generation will be the same as the original parent generation.

4. Hardy-Weinberg Equilibrium • There are five conditions that must be met for Hardy Weinberg Equilibrium to occur in a population (no changes in allele frequencies): • large population • random mating • no mutations • no gene flow • no selection

5. Large Population • A large population is less likely to have random fluctuations change allele frequencies than smaller populations. • Small populations are more likely to experience genetic drift- change in allele frequency by chance • Think of a coin toss. The more you toss the coin, the greater your chances of flipping 50% heads and 50% tails.

6. Random Mating • Individuals must randomly mate with other individuals within a population. • Non-random mating will result in changes in allele frequency.

7. Non-Random Mating • Types of non-random mating: • Assortative mating- choosing mates with similar phenotypes • Competition- some males compete for mates

8. Mutations • Mutations- Spontaneous changes in an allele. • Increase variation in a population when old alleles change into new alleles.

9. Gene Flow • Gene flow- caused by migration. • New alleles are introduced into a population when new individuals move in. • Alleles are removed from the population when individuals move out of a population.

10. Natural selection tends to reduce genetic variability. -Three types: Stabilizing Disruptive Directional Selection

11. Stabilizing selection eliminates those phenotypes most different from the norm, thus reducing the frequency of phenotypic extremes. (AA, aa) Directional selection eliminates one extreme and moves the population toward the other. (AA or aa) Disruptive selection eliminates average phenotypes and encourages the extremes. (Aa) This tends to result in distinct phenotypes in the same population. Selection

12. Hardy-Weinberg Equilibrium • For all populations to maintain equilibrium (no changes in allele frequencies over many generations) all five conditions must be met. • large population (no genetic drift) • random mating • no mutations • no gene flow • no selection

13. Hardy-Weinberg Equilibrium • When one condition changes, the gene pool or allele frequency of the population will change. • These changes result in different genotypes and phenotypes (increased variation) in the population.

14. Hardy-Weinberg Equilibrium • A population that is not in Hardy-Weinberg equilibrium will undergo natural selection because of genetic variation. • Natural selection will ultimately favor the most fit individual(s) in the population. • This will result in changes in a population over time- EVOLUTION OCCURS!

15. How would a mutation cause changes in allele frequency in a population? How would this allow evolution to occur? Hardy-Weinberg Equilibrium

16. Hardy-Weinberg Equilibrium • How would a small population affect allele frequencies over several generations? • How would this allow evolution to occur? Cheetah

17. Hardy-Weinberg Equilibrium • How would gene flow affect allele frequencies in a population? • How would this allow evolution to occur?

18. Hardy-Weinberg Equilibrium • How would natural selection change allele frequencies in a population? • How does this allow evolution to occur?

19. Hardy-Weinberg Equilibrium • How would choosing a mate change allele frequencies in a population? • How would this allow evolution to occur?

20. Mechanisms for Change • When populations are not in Hardy-Weinberg Equilibrium, evolution occurs. • The conditions that upset Hardy-Weinberg equilibrium are known as the mechanisms of change. • Cause changes in alleles in a population.

21. Mechanisms of Evolution • Genetic Variation • Descent and the genetic differences that are heritable and passed on to the next generation; • Mutation, migration (gene flow), genetic drift, non-random mating, and natural selection as mechanisms for change; • Result in changes over time- Evolution!