Chapter18

3,489 views
3,309 views

Published on

Published in: Education
0 Comments
4 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
3,489
On SlideShare
0
From Embeds
0
Number of Embeds
7
Actions
Shares
0
Downloads
95
Comments
0
Likes
4
Embeds 0
No embeds

No notes for slide

Chapter18

  1. 1. Process of Evolution Chapter 18
  2. 2. Evolution in a Genetic Context (Population Genetics) <ul><li>Microevolution </li></ul><ul><ul><li>Change in gene frequency in a population over time </li></ul></ul><ul><ul><ul><li>Gene pool = ALL alleles at ALL gene loci in ALL individuals of the population. </li></ul></ul></ul><ul><ul><ul><li>Allelic frequency = # specific alleles total alleles in population Shown as f A or f a (f followed by subscript) </li></ul></ul></ul><ul><ul><ul><ul><li>Indicates probability of allele </li></ul></ul></ul></ul>
  3. 3. Microevolution What could cause CHANGES in allele frequencies?
  4. 4. Causes of Microevolution <ul><li>Genetic Mutations </li></ul><ul><ul><li>Mutated alleles (or combinations of alleles) may be more adaptive </li></ul></ul><ul><li>Gene Flow </li></ul><ul><ul><li>Movement of alleles between populations by migration of breeding individuals. </li></ul></ul><ul><ul><ul><li>Continual gene flow reduces variability (differences) between populations. </li></ul></ul></ul>
  5. 5. Gene Flow
  6. 6. Causes of Microevolution <ul><li>Nonrandom Mating </li></ul><ul><ul><li>Individuals do not choose mates randomly. </li></ul></ul><ul><ul><ul><li>Assortative mating - Individuals tend to mate with those with the same phenotype. </li></ul></ul></ul><ul><ul><ul><li>Sexual selection - Males compete for the right to reproduce and females choose to mate with males possessing a particular phenotype. </li></ul></ul></ul>
  7. 7. Causes of Microevolution <ul><li>Genetic Drift </li></ul><ul><ul><li>Changes in allele frequencies of a gene pool due to CHANCE. </li></ul></ul><ul><ul><ul><li>EX: natural disaster, weather change </li></ul></ul></ul><ul><ul><ul><li>Larger effect in small populations. </li></ul></ul></ul>
  8. 8. Genetic Drift <ul><li>Bottleneck Effect </li></ul><ul><ul><li>Event prevents majority of genotypes from entering the next generation </li></ul></ul>
  9. 9. Genetic Drift <ul><li>Founder Effect </li></ul><ul><ul><li>Subgroup starts new population </li></ul></ul><ul><ul><ul><li>Alleles carried by population founders are dictated by chance </li></ul></ul></ul><ul><ul><ul><li>Founding population does NOT reflect original population </li></ul></ul></ul>
  10. 10. Founder effect Sample of original population Descendants Founding population B Founding population A
  11. 11. Natural Selection <ul><li>Natural Selection results in adaptation of a population to the environment </li></ul><ul><ul><li>Adaptation is result of new allele frequencies </li></ul></ul>
  12. 12. Hardy-Weinberg Principle <ul><li>Hardy-Weinberg equilibrium = NO </li></ul><ul><li>microevolution </li></ul><ul><li>** Allele frequencies of gene pool will stay the SAME (equilibrium) IF </li></ul>
  13. 13. Hardy-Weinberg Principle <ul><li>** Allele frequencies of gene pool will stay the same (equilibrium) IF </li></ul>What could cause CHANGES in allele frequencies?
  14. 14. Hardy-Weinberg Principle <ul><li>** Allele frequencies of gene pool will stay the same (equilibrium) IF </li></ul><ul><ul><li>No Mutations </li></ul></ul><ul><ul><li>No Gene Flow </li></ul></ul><ul><ul><li>Random Mating </li></ul></ul><ul><ul><li>No Genetic Drift </li></ul></ul><ul><ul><li>No Selection </li></ul></ul>
  15. 15. Hardy-Weinberg <ul><li>Under real conditions, these conditions are rarely, if ever, met, and allele frequencies in the gene pool of a population change between generations. </li></ul><ul><ul><li>Evolution has occurred. </li></ul></ul>
  16. 16. Hardy-Weinberg Math <ul><li>Consider a trait with 2 possible alleles… </li></ul><ul><li>p = frequency of dominant allele </li></ul><ul><ul><li>The probability that an allele chosen at random is dominant </li></ul></ul><ul><li>q = frequency of recessive allele </li></ul><ul><ul><li>The probability that an allele chosen at random is recessive </li></ul></ul><ul><li>p + q = 1; Why? </li></ul>
  17. 17. Hardy-Weinberg Math <ul><li>p = frequency of dominant allele </li></ul><ul><ul><li>The probability that an allele chosen at random is dominant </li></ul></ul><ul><li>q = frequency of recessive allele </li></ul><ul><ul><li>The probability that an allele chosen at random is recessive </li></ul></ul><ul><li>p + q = 1; Why? </li></ul><ul><li>If there are only two allele possibilities, the sum of their frequencies must be 1 </li></ul>
  18. 18. Hardy-Weinberg Math <ul><li>What is the probability of an individual being homozygous dominant (AA) – the frequency of the AA genotype? </li></ul><ul><li>What is the probability of an individual being homozygous recessive (aa)? </li></ul>
  19. 19. Hardy-Weinberg Math <ul><li>What is the probability of an individual being homozygous dominant (AA) – the frequency of the AA genotype? </li></ul><ul><li>f AA = p x p = p 2 </li></ul><ul><li>What is the probability of an individual being homozygous recessive (aa)? </li></ul><ul><li>f aa = q x q = q 2 </li></ul>
  20. 20. Hardy-Weinberg Math <ul><li>What is the probability of an individual being heterozygous (Aa) – the frequency of the Aa genotype? </li></ul>
  21. 21. Hardy-Weinberg Math <ul><li>What is the probability of an individual being heterozygous ( Aa ) – the frequency of the Aa genotype? </li></ul><ul><li>f Aa = (p x q) + (q x p) = 2pq </li></ul><ul><li>There are 2 possible combinations: </li></ul><ul><ul><li>allele 1 can be A and allele 2 can be a </li></ul></ul><ul><ul><li>OR </li></ul></ul><ul><ul><li>allele 1 can be a and allele 2 can be A </li></ul></ul>
  22. 22. Hardy Weinberg Math <ul><li>Remember: p + q = 1 </li></ul><ul><li>AND </li></ul><ul><li>(p + q) 2 = p 2 + 2pq + q 2 = 1 </li></ul><ul><li>q 2 is usually known! (What does q 2 refer to?) </li></ul>
  23. 23. H-W Practice: Practice Problems 18.1 <ul><li>1. In a certain population, 21% are homozygous dominant, 49% heterozygous, and 30% homozygous recessive. What percentage of the next generation is predicted to be homozygous dominant, assuming a Hardy-Weinberg equilibrium? </li></ul>
  24. 24. H-W Practice: Practice Problems 18.1 <ul><li>1. In a certain population, 21% are homozygous dominant, 49% heterozygous, and 30% homozygous recessive. What percentage of the next generation is predicted to be homozygous dominant, assuming a Hardy-Weinberg equilibrium? </li></ul><ul><li>If it is in Hardy-Weinberg equilibrium, we would expect the same genotypic frequencies in the next generation. </li></ul><ul><li>21% homozygous dominant </li></ul><ul><li>Let’s do the math! </li></ul>
  25. 25. H-W Practice: Practice Problems 18.1 <ul><li>1. In a certain population, 21% are homozygous dominant, 49% heterozygous, and 30% homozygous recessive. What percentage of the next generation is predicted to be homozygous dominant, assuming a Hardy-Weinberg equilibrium? </li></ul><ul><li>q 2 = .30 so q = √.30 = 0.55 </li></ul><ul><li>p + q = 1, so p = 1 – q = 1 – 0.55 = 0.45 </li></ul><ul><li>p 2 = (0.45) 2 = 0.2025 </li></ul><ul><li>Cheap example! </li></ul>
  26. 26. H-W Practice: Practice Problems 18.1 <ul><li>2. Of the members of a population of pea plants, 9% are short (recessive). What are the frequencies of the recessive allele t and the dominant allele T ? What are the genotypic frequencies of the population? </li></ul>
  27. 27. H-W Practice: Practice Problems 18.1 <ul><li>2. Of the members of a population of pea plants, 9% are short (recessive). What are the frequencies of the recessive allele t and the dominant allele T ? What are the genotypic frequencies of the population? </li></ul><ul><li>q 2 = .09 so q = √.09 = 0.30 </li></ul><ul><li>f t = 0.3 </li></ul><ul><li>p + q = 1, so p = 1 – q = 1 – 0.30 = 0.70 </li></ul><ul><li> f T = 0.7 </li></ul>
  28. 28. H-W Practice: Practice Problems 18.1 <ul><li>2. Of the members of a population of pea plants, 9% are short (recessive). What are the frequencies of the recessive allele t and the dominant allele T ? What are the genotypic frequencies of the population? </li></ul><ul><li>f t = 0.3 f T = 0.7 </li></ul><ul><li>f TT = p 2 = (0.7) 2 = 0.49 </li></ul><ul><li>f Tt = 2pq = (2 x 0.3 x 0.7) = 0.42 </li></ul><ul><li>f tt = q 2 = (0.3) 2 = 0.09 </li></ul>f TT = 0.49 f Tt = 0.42 f TT = 0.09
  29. 29. Types of Selection <ul><li>Directional Selection </li></ul><ul><ul><li>An extreme phenotype is favored and the distribution curve shifts in that direction. </li></ul></ul><ul><ul><ul><li>Can occur when a population is adapting to a changing environment. </li></ul></ul></ul>
  30. 30. Directional Selection
  31. 31. Types of Selection <ul><li>Stabilizing Selection </li></ul><ul><ul><li>Occurs when an intermediate phenotype is favored. </li></ul></ul><ul><ul><ul><li>Can improve adaptation of the population to constant conditions. </li></ul></ul></ul>
  32. 32. Stabilizing Selection
  33. 33. Types of Selection <ul><li>Disruptive Selection </li></ul><ul><ul><li>Two or more extreme phenotypes are favored over any intermediate phenotype. </li></ul></ul><ul><ul><ul><li>Two distinctly different phenotypes are found in the population. </li></ul></ul></ul>
  34. 34. Disruptive Selection
  35. 35. Maintenance of Variations <ul><li>Maintenance of variation is beneficial because populations with limited variation may not be able to adapt to new conditions. </li></ul><ul><ul><li>Only exposed alleles are subject to natural selection. </li></ul></ul><ul><ul><ul><li>Sickle-Cell Disease </li></ul></ul></ul><ul><ul><ul><ul><li>Homozygote remains in equilibrium in some regions of Africa because the heterozygote is protected from sickle-cell and malaria. </li></ul></ul></ul></ul><ul><li>http://www.pbs.org/wgbh/evolution/library/01/2/l_012_02.html </li></ul>
  36. 36. Speciation <ul><li>Speciation is the splitting of one species into two or more species, or the transformation of one species into a new species over time. </li></ul><ul><ul><li>Species Definition </li></ul></ul><ul><ul><ul><li>Morphological </li></ul></ul></ul><ul><ul><ul><li>Biological </li></ul></ul></ul><ul><ul><ul><ul><li>Reproductive Isolation </li></ul></ul></ul></ul><ul><ul><ul><li>Phylogenetic </li></ul></ul></ul>
  37. 37. Reproductive Isolating Mechanisms <ul><li>Prezygotic Isolating Mechanisms </li></ul><ul><ul><li>Prevent reproduction attempts, and make it unlikely fertilization will be successful. </li></ul></ul><ul><ul><ul><li>Habitat Isolation </li></ul></ul></ul><ul><ul><ul><li>Temporal Isolation </li></ul></ul></ul><ul><ul><ul><li>Behavioral Isolation </li></ul></ul></ul><ul><ul><ul><li>Mechanical Isolation </li></ul></ul></ul><ul><ul><ul><li>Gamete Isolation </li></ul></ul></ul>
  38. 38. Reproductive Isolating Mechanisms <ul><li>Postzygotic Isolating Mechanisms </li></ul><ul><ul><li>Prevent hybrid offspring from developing or breeding. </li></ul></ul><ul><ul><ul><li>Zygote Mortality </li></ul></ul></ul><ul><ul><ul><li>Hybrid Sterility </li></ul></ul></ul><ul><ul><ul><li>F 2 Fitness </li></ul></ul></ul>
  39. 39. Modes of Speciation <ul><li>Allopatric Speciation </li></ul><ul><ul><li>Occurs when one population is geographically isolated from other populations. </li></ul></ul><ul><li>Sympatric Speciation </li></ul><ul><ul><li>A population develops into two or more reproductively isolated groups without prior geographic isolation. </li></ul></ul><ul><ul><li>Common in plants – polyploidy </li></ul></ul>
  40. 40. Adaptive Radiation <ul><li>Adaptive Radiation is an example of allopatric speciation. </li></ul><ul><ul><li>Many new species evolve from a single ancestral species when members of the species become adapted to different environments. </li></ul></ul>

×