1 / 44

BIOE 109 Summer 2009 Lecture 5- Part I Hardy- Weinberg Equilibrium

BIOE 109 Summer 2009 Lecture 5- Part I Hardy- Weinberg Equilibrium. The Hardy-Weinberg-Castle Equilibrium. The Hardy-Weinberg-Castle Equilibrium. Godfrey Hardy. Wilhelm Weinberg. William Castle. Conclusions of the Hardy-Weinberg principle. Conclusions of the Hardy-Weinberg principle

ivi
Download Presentation

BIOE 109 Summer 2009 Lecture 5- Part I Hardy- Weinberg Equilibrium

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. BIOE 109 Summer 2009 Lecture 5- Part I Hardy- Weinberg Equilibrium

  2. The Hardy-Weinberg-Castle Equilibrium

  3. The Hardy-Weinberg-Castle Equilibrium Godfrey Hardy Wilhelm Weinberg William Castle

  4. Conclusions of the Hardy-Weinberg principle

  5. Conclusions of the Hardy-Weinberg principle 1. Allele frequencies will not change from generation to generation.

  6. Conclusions of the Hardy-Weinberg principle 1. Allele frequencies will not change from generation to generation. 2. Genotype proportions determined by the “square law”.

  7. Conclusions of the Hardy-Weinberg principle 1. Allele frequencies will not change from generation to generation. 2. Genotype proportions determined by the “square law”. • for two alleles = (p + q)2 = p2 + 2pq + q2

  8. Conclusions of the Hardy-Weinberg principle 1. Allele frequencies will not change from generation to generation. 2. Genotype proportions determined by the “square law”. • for two alleles = (p + q)2 = p2 + 2pq + q2 • for three alleles (p + q + r)2 = p2 + q2 + r2 + 2pq + 2pr +2qr

  9. Conclusions of the Hardy-Weinberg principle  3. Hardy-Weinberg equilibrium occurs independently of allelic frequencies

  10. Conclusions of the Hardy-Weinberg principle  3. Hardy-Weinberg equilibrium occurs independently of allelic frequencies Allele frequencies Genotype frequencies A1 = 0.80, A2 = 0.20 A1A1 = 0.64, A1A2 = 0.32, A2A2 = 0.04

  11. Conclusions of the Hardy-Weinberg principle  3. Hardy-Weinberg equilibrium occurs independently of allelic frequencies Allele frequencies Genotype frequencies A1 = 0.80, A2 = 0.20 A1A1 = 0.64, A1A2 = 0.32, A2A2 = 0.04 A1 = 0.50, A2 = 0.50 A1A1 = 0.25, A1A2 = 0.50, A2A2 = 0.25

  12. Conclusions of the Hardy-Weinberg principle  3. Hardy-Weinberg equilibrium occurs independently of allelic frequencies Allele frequencies Genotype frequencies A1 = 0.80, A2 = 0.20 A1A1 = 0.64, A1A2 = 0.32, A2A2 = 0.04 A1 = 0.50, A2 = 0.50 A1A1 = 0.25, A1A2 = 0.50, A2A2 = 0.25 A1 = 0.10, A2 = 0.90 A1A1 = 0.01, A1A2 = 0.18, A2A2 = 0.81

  13. Assumptions of Hardy-Weinberg equilibrium

  14. Assumptions of Hardy-Weinberg equilibrium 1. Mating is random

  15. Assumptions of Hardy-Weinberg equilibrium 1. Mating is random… but some traits experience positive assortative mating

  16. Assumptions of Hardy-Weinberg equilibrium 1. Mating is random 2. Population size is infinite (i.e., no genetic drift)

  17. Assumptions of Hardy-Weinberg equilibrium 1. Mating is random 2. Population size is infinite (i.e., no genetic drift) 3. No migration

  18. Assumptions of Hardy-Weinberg equilibrium 1. Mating is random 2. Population size is infinite (i.e., no genetic drift) 3. No migration 4. No mutation

  19. Assumptions of Hardy-Weinberg equilibrium 1. Mating is random 2. Population size is infinite (i.e., no genetic drift) 3. No migration 4. No mutation 5. No selection

  20. Hardy-Weinberg principle: A null model 1. Mating is random 2. Population size is infinite (i.e., no genetic drift) 3. No migration 4. No mutation 5. No selection The Hardy-Weinberg equilibrium principle thus specifies conditions under which the population will NOT evolve. In other words, H-W principle identifies the set of events that can cause evolution in real world.

  21. Does Hardy-Weinberg equilibrium ever exist in nature?

  22. Does Hardy-Weinberg equilibrium ever exist in nature? Example: Atlantic cod (Gadus morhua) in Nova Scotia

  23. Does Hardy-Weinberg equilibrium ever exist in nature? Example: Atlantic cod (Gadus morhua) in Nova Scotia as a juvenile…

  24. Does Hardy-Weinberg equilibrium ever exist in nature? Example: Atlantic cod (Gadus morhua) in Nova Scotia … and as an adult

  25. Does Hardy-Weinberg equilibrium ever exist in nature? Example: Atlantic cod (Gadus morhua) in Nova Scotia • a sample of 364 fish were scored for a single nucleotide polymorphism (SNP)

  26. Does Hardy-Weinberg equilibrium ever exist in nature? Example: Atlantic cod (Gadus morhua) in Nova Scotia • a sample of 364 fish were scored for a single nucleotide polymorphism (SNP) A1A1 = 109 A1A2 = 182 A2A2 = 73

  27. Does Hardy-Weinberg equilibrium ever exist in nature? Example: Atlantic cod (Gadus morhua) in Nova Scotia • a sample of 364 fish were scored for a single nucleotide polymorphism (SNP) A1A1 = 109 A1A2 = 182 A2A2 = 73 Question: Is this population in Hardy-Weinberg equilibrium?

  28. Testing for Hardy-Weinberg equilibrium

  29. Testing for Hardy-Weinberg equilibrium Step 1: Estimate genotype frequencies

  30. Testing for Hardy-Weinberg equilibrium Step 1: Estimate genotype frequencies Step 2: Estimate allele frequencies

  31. Testing for Hardy-Weinberg equilibrium Step 1: Estimate genotype frequencies Step 2: Estimate allele frequencies Step 3: Estimate expected genotype frequencies under the assumption of H-W equilibrium

  32. Testing for Hardy-Weinberg equilibrium Step 1: Estimate genotype frequencies Step 2: Estimate allele frequencies Step 3: Estimate expected genotype frequencies under the assumption of H-W equilibrium Step 4: Compare observed and expected numbers of genotypes 2 = (Obs. – Exp.)2 Exp.

  33. A simple model of directional selection

  34. Persistent selection changes allele frequencies over generations (Obvious) Conclusion: Natural selection can cause rapid evolutionary change!

  35. A simple model of directional selection • consider a single locus with two alleles A and a

  36. A simple model of directional selection • consider a single locus with two alleles A and a • let p = frequency of A allele

  37. A simple model of directional selection • consider a single locus with two alleles A and a • let p = frequency of A allele • let q = frequency of a allele

  38. A simple model of directional selection • consider a single locus with two alleles A and a • let p = frequency of A allele • let q = frequency of a allele • relative fitnesses are: AA Aa aa w11 w12 w22

  39. A simple model of directional selection • consider a single locus with two alleles A and a • let p = frequency of A allele • let q = frequency of a allele • relative fitnesses are: AA Aa aa w11 w12 w22 • it is also possible to determine relative fitness of the A and a alleles:

  40. A simple model of directional selection • consider a single locus with two alleles A and a • let p = frequency of A allele • let q = frequency of a allele • relative fitnesses are: AA Aa aa w11 w12 w22 • it is also possible to determine relative fitness of the A and a alleles: let w1 = fitness of the A allele

  41. A simple model of directional selection • consider a single locus with two alleles A and a • let p = frequency of A allele • let q = frequency of a allele • relative fitnesses are: AA Aa aa w11 w12 w22 • it is also possible to determine relative fitnesses of the A and a alleles: let w1 = fitness of the A allele let w2 = fitness of the a allele

  42. The fitness of the A allele = w1 = pw11 + qw12

  43. The fitness of the A allele = w1 = pw11 + qw12 The fitness of the a allele = w2 = qw22 + pw12

  44. Directional selection • let p = frequency of A allele • let q = frequency of a allele • relative fitness of different genotypes are: AA Aa aa w11 w12 w22 • it is also possible to determine relative fitness of the A and a alleles: The fitness of the A allele = w1 = pw11 + qw12 The fitness of the a allele = w2 = qw22 + pw12 • Mean population fitness = w = pw1 + qw2

More Related