Hardy-Weinberg equilibrium describes populations that are not evolving.

1. KEY CONCEPT Hardy-Weinberg equilibrium provides a framework for understanding how populations evolve. • named after Godfrey Hardy (mathematician at Cambridge) and William Weinberg (German physician) who discovered this mathematical relationship in 1908

2. Hardy-Weinberg equilibrium describes populations that are not evolving. • Biologists use models to study populations. • Hardy-Weinberg equilibrium is a type of model.

3. What are the “agents” of evolutionary change? • In other words…. What factors drive evolution?

4. AGENTS OF EVOLUTIONARY CHANGE: • (A) mutation, a change in DNA • (B) gene flow, the migration of alleles from one population to another • (C) non-random mating • (D) genetic drift, a change in allele frequencies in a small population due to a chance event • (E) natural selection for favourable variations.

5. Hardy-Weinberg equilibrium describes populations that are NOT evolving. • Genotype frequencies stay the same if five conditions are met. • very large population: no genetic drift • no emigration or immigration: no gene flow • no mutations: no new alleles added to gene pool • random mating:no sexual selection • no natural selection:all traits aid equallyin survival

6. Hardy-Weinberg equilibrium describes populations that are not evolving. • Real populations RARELY meet all five conditions. • Real population data iscompared to a model. • Models are used tostudy how populationsevolve.

7. Genetic drift changes allele frequencies due to chance alone.

8. Gene flow moves alleles from one population to another.

9. Mutations produce the genetic variation needed for evolution.

10. Sexual selection selects for traits that improve mating success.

11. Natural selection selects for traits advantageous for survival.

12. A quick review of genetics definitions: A group of organisms of the same species occupying the same area at the same time. • Population: • Gene: A section of DNA that codes for a specific protein. • Alleles: The different forms of the gene (one from each parent) • Gene pool: The sum of all the alleles for the different genes in the population. • Genotype frequency: The proportion (%) of a population with a specific genotype. • Phenotype frequency: The proportion (%) of a population with a specific phenotype. The rate of occurrence of a particular allele in a population (usually expressed as a decimal). • Allele frequency:

13. HARDY-WEINBERG EQUILIBRIUM Allele frequencies in a population will remain the same from one generation to the next, provided 5 conditions are met: 1. The population is large enough that chance events will not alter allele frequencies. 2. Mates are chosen on a random basis. 3. There are no net mutations. 4. There is no migration. 5. There is no natural selection against any of the phenotypes. For a trait with two alleles, the sum of the allele frequencies must be 1.0 or 100%

14. HARDY-WEINBERG EQUILIBRIUM The Hardy-Weinberg equilibrium is used to determine the frequencies of different genotypes and phenotypes in the population.

16. "The Hardy-Weinberg equation is based on Mendelian genetics. It is derived from a simple Punnett square in which p is the frequency of the dominant allele and q is the frequency of the recessive allele." The Hardy-Weinberg equation is used to predict genotype frequencies in a population. • Predicted genotype frequencies are compared with actual frequencies. • used for traits in simple dominant-recessive systems • must know frequency of recessive homozygotes • p2 + 2pq + q2 = 1

17. HARDY-WEINBERG PRACTICE PROBLEMS 1. If 98 out of 200 individuals in a population express the recessive phenotype, what percent of the population are homozygous dominant?

18. In humans, blonde hair is recessive (b) to brown hair (B). If a population of 100 individuals has 36 blonde-haired people, what is: • The allele frequency of brown hair • The frequency of brown-haired individuals • The frequency of homozygous brown-haired individuals

19. 3. 1 in 3600 Canadian newborns have cystic fibrosis. C (normal) is dominant over c (cystic fibrosis). The inheritance pattern of cystic fibrosis is: a) Using this information, how many people in Canada are potential carriers of this disease? (the population of Canada is 34 278 400 as of January 2011)

20. HARDY-WEINBERG PROBLEMS Answer the questions below in the spaces provided. 1. A population of birds is in Hardy-Weinberg (genetic) equilibrium. 20 percent of the birds have short tail feathers, which is a recessive trait. Determine the genotype and allele frequencies of the population.

21. 2. In a population of ferns, a biologist has determined that 60 percent of leaf-shape genes in the population carry the dominant allele for curly leaves (C). The remaining 40 percent of the genes carry the recessive allele for straight leaves (c). Determine the genotype and allele frequencies of the next generation of ferns. Use a Punnett square to show your work.

22. 3. Allele Z is dominant, and is present in a population at a frequency of 37 per 100 individuals. Assuming the population is in Hardy-Weinberg equilibrium, what proportion of individuals in the population would be expected to be (a) homozygous dominant, (b) heterozygous, and (c) homozygous recessive? Show your work.

23. 4. In a large, random-mating population, 85 in every 1000 humans carry the recessive allele for red hair. a)What percentage of the population carries this allele but does not exhibit red hair? ___________________________________________________ b)Would you expect to see a change in allele frequencies if members of this population preferentially mated with individuals with red hair? Explain your answer.

24. 5. If a small, random-mating population has 18 percent of individuals exhibiting a recessive trait, could you calculate the genotype and allele frequencies of the next generation? Explain your answer.

25. 6. 45 percent of individuals in a population of raccoons have a recessive trait. If the population is in Hardy-Weinberg equilibrium, calculate the frequency of the dominant allele in the population.

26. expected in all populations most of the time • respond to changing environments • In nature, populations evolve.

27. SPECIATIONKEY CONCEPTNew species can arise when populations are isolated.

28. The isolation of populations can lead to speciation. • Populations become isolated when there is no gene flow. • Isolated populations adapt to their own environments. • Genetic differences can add up over generations.

29. Reproductive isolation can occur between isolated populations. • members of different populations cannot mate successfully • final step to becoming separate species • Speciation is the rise of two or more species from one existing species.

30. Populations can become isolated in several ways. • Behavioral barriers can cause isolation. • called behavioral isolation • includes differences in courtship or mating behaviors

31. called geographic isolation • physical barriers divide population • Geographic barriers can cause isolation. • Temporal barriers can cause isolation. • called temporal isolation • timing of reproductive periods prevents mating