1. Ch. 21 Warm-Up
Define the following terms: population, population genetics, gene pool, fitness
What does Hardy-Weinberg indicate?
What is 1 thing you are grateful for today?

2. Warm-Up
In a population of 200 mice, 98 are homozygous dominant for brown coat color (BB), 84 are heterozygous (Bb), and 18 are homozygous (bb).
The allele frequencies of this population are:
B allele: ___ b allele: ___
The genotype frequencies are:
BB: ___ Bb: ___ bb: ___
Use the above info to determine the genotype frequencies of the next generation:
B (p): ___ b (q): ___
BB (p2): ___ Bb (2pq): ___
bb (q2): ___

3. Warm-Up
The scarlet tiger moth has the following genotypes. Calculate the allele and genotype frequencies (%) for a population of 1612 moths.
AA = 1469 Aa = 138 aa = 5
A = ___ a = ___
AA =
Aa =
aa =

4. Warm-Up
Use the following information to help you answer the question below:
Population = 1000 people
AA = 160 Aa = 480 aa = 360
What are the genotype ratios? Allele frequencies?
Use directional, stabilizing or disruptive selection to explain the following:
Butterflies in 2 different colors that resemble other species
Birds produce 4-5 eggs per clutch
Average human baby weighs 7 lbs.
Darwin’s finches and beak size during drought

5. Warm-Up
Determine if the following examples are directional, disruptive, or stabilizing selection:
Butterflies in 2 different colors each represent a species distasteful to birds
Brightly colored birds mate more frequently than drab birds of same species
Fossil evidence of horse size increasing over time
Average birth weight is 7 lbs.

6. The Evolution of Populations
Chapter 21
The Evolution of Populations

7. What you must know: Mutations are the only source of new genes.
The three ways in which sexual reproduction produces genetic variation.
The conditions for Hardy-Weinberg equilibrium.
How to use the Hardy-Weinberg equation to calculate allele frequencies to test whether a population is evolving.
What effects genetic drift, migration, or selection may have on a population, and analyze data to justify your predictions.

8. Chapter 21 The Evolution of Populations
Part A (Sec & 21.2): Microevolution and the Hardy-Weinberg Equation

9. What you must know: Mutations are the only source of new genes.
The three ways in which sexual reproduction produces genetic variation.
The conditions for Hardy-Weinberg equilibrium.
How to use the Hardy-Weinberg equation to calculate allele frequencies to test whether a population is evolving.

10. The evolutionary impact of natural selection is only apparent in the changes in a population of organisms over time.

11. Microevolution Evolution on smallest scale
Change in allele frequencies in a population over generations.

12. Mechanisms that cause allele frequency change:

13. Genetic Variation
Darwin’s could not explain how inherited variations are maintained in populations - not “trait blending”
A few years after Darwin’s “Origin of Species”, Gregor Mendel proposed his hypothesis of inheritance:
Parents pass on discrete heritable units (genes) that retain their identities in offspring
- Genetic variation: differences among individuals in the composition of their genes or other DNA sequence.

14. Without genetic variation, evolution cannot occur.

15. Variation between populations Geographic variation: differences in the genetic composition of separate populations.

17. Sources of Genetic Variation
Mutations = only source of new genes and new alleles
Mutations in gametes passed to offspring
Point mutations
Chromosomal mutations  gene duplication
Fast reproduction
Normally every1/100,000 genes per generation in animals and plants in prokaryotes: mutations can quickly generate genetic variation( short life- span), the same in viruses. Example : HIV has a 2 days life span, with RNA which ahs a higher rate of mutation than DNA( lack of repair mechanisms in the host for RNA)- Most effective medicine for it is drug” cocktail”( combination of several drugs).
Sexual reproduction: shuffle existing alleles:
Crossing over, independent assortment, random fertilization

20. Example

21. Population: group of individuals of same species that live in the same area and interbreed, producing fertile offspring
Population genetics: study of how populations change genetically over time

22. Gene Pool All alleles at all loci in all the members of a population
Fixed allele: all members of a population are homozygous for same allele
More fixed alleles  less genetic diversity

23. Hardy-Weinberg Equilibrium
Describes a population that is NOT evolving
Frequencies of alleles & genotypes in a population’s gene pool remain constant over generations, provided that only Mendelian segregation and recombination of alleles are at work.

25. Conditions for Hardy-Weinberg Equilibrium
No mutations.
Random mating. (no sexual selection)
No natural selection.
Extremely large population size. (no genetic drift)
No gene flow. (no emigration, immigration)
If ANY of these conditions are NOT met  Microevolution occurs!

26. Applying the Hardy-Weinberg Equation

27. p + q = 1 Hardy-Weinberg Equation Note: 1 – p = q 1 – q = p
Allele Frequencies:
Gene with 2 alleles : p, q
p = frequency of A, dominant allele
q = frequency of a, recessive allele
Note:
1 – p = q
1 – q = p
p + q = 1

28. p2 + 2pq + q2 = 1 Hardy-Weinberg Equation Genotype Frequencies:
3 genotypes (AA, Aa, aa)
p2 + 2pq + q2 = 1
p2 = AA (homozygous dominant)
2pq = Aa (heterozygous)
q2 = aa (homozygous recessive)

29. Example 1: PTC Tasters
Tasters (TT or Tt), Nontasters (tt) Tasters = ____ Nontasters = ____ Total = ____ q2 = q = p + q = 1 p = 1 – q = p2 + 2pq + q2 = 1

30. Example 2: Plant Population
Suppose in a plant population, red flowers (R) is dominant to white flowers (r). In a population of 500 individuals, 25% show the recessive phenotype. How many individuals would you expect to be homozygous dominant and heterozygous for this trait?

31. Chapter 21 The Evolution of Populations
Part B (Sec & 21.4): Mechanisms of Evolution and Types of Selection

32. What you must know:
What effects genetic drift, migration, or selection may have on a population, and analyze data to justify your predictions.

33. Hardy-Weinberg Equilibrium
In nature, it is NOT likely all the conditions for H-W Equilibrium will be met  Populations are evolving
Allele/genotype frequency changes due to mutations and nonrandom mating are minor
Three MAJOR mechanisms of evolution:
Natural Selection
Genetic Drift
Gene Flow

34. Mechanisms of Microevolution
Natural Selection: differential reproductive success
Rock Pocket Mice

35. Mechanisms of Microevolution
Genetic Drift: unpredictable fluctuation of alleles from one generation to next
Significant genetic drift in small populations
Allele frequencies change at random. It can cause the frequency of such an allele to decrease and also can cause it to slightly increase.
Can lose genetic variation in populations.
Can cause harmful alleles to become fixed
Types:
Founder Effect
Bottleneck Effect

36. Genetic drift

37. Certain alleles may be over/under represented
Bottleneck Effect: severe drop in population size because of sudden changes in environment( flood, fire).
Certain alleles may be over/under represented
Human actions sometimes create severe bottlenecks for other species
Elephant seals have reduced genetic variation due to hunting
Florida panthers in danger of extinction

38. Polydactyly in Amish population
Founder Effect: few individuals become isolated from larger population, they may establish a new population whose gene pool differs from the source population.  certain alleles over/under represented.
Blown by storm in new island
High frequency of certain inherited disorder in human
Polydactyly in Amish population

39. Mechanisms of Microevolution
Gene Flow: population gains/loses alleles due to immigration or emigration.
Increase the frequencies of alleles that improve the match between organisms and their environment, but neither does so consistently.
May introduce alleles that are advantageous or ones that are disadvantageous.
Worldwide spread of insecticide-resistant alleles in Culex pipiens mosquitoes (West Nile vector)

40. A Closer Look at Natural Selection

41. Relative Fitness: contribution an individual makes to the gene pool of the next generation relative to contribution of others
Natural selection can occur in 3 ways:
Directional Selection
Disruptive Selection
Stabilizing Selection

42. Directional Selection: Eg
Directional Selection: Eg. beak sizes of birds during wet/dry seasons in Galapagos
Disruptive Selection:
Eg. small beaks for small seeds; large beaks for large seeds
Stabilizing Selection: Eg. average human birth weight

43. The key role of natural selection in adaptive evolution
Examples: Cuttlefish: change color rapidly, blend into different backgraounds.
Jaws of snakes: allo them to swallow prey much larger than their own head.
Version of an enzyme that shows improved function in cold environments.
These adaptations can arise gradually over time as natural selection increases the frequencies of alleles that enhance survival and reproduction. As the proportion of individuals that have favorable traits increases, the match between a species and its environment improves; that is , adaptive evolution occurs.
Adaptive evolution is a continuous , dynamic process.

44. Balancing Selection Diploidy: inherit 2 alleles
Recessive alleles hidden in heterozygotes
Heterozygote advantage: heterozygotes have better survival
Eg. heterozygotes for sickle cell anemia protected against malaria

45. Sexual Selection Certain individuals more likely to obtain mates
Sexual dimorphism: difference between 2 sexes (size, color, ornamentation, behavior)
Intra sexual selection: competition within same sex
Intersexual selection: mate choice
Sexual selection may lead to pronounced secondary differences between the sexes

46. Natural selection cannot fashion perfect organisms.
Selection can only edit existing variations.
Evolution is limited by historical constraints.
Adaptations are often compromises.
Chance, natural selection, and the environment interact.

47. BioFlix: Mechanisms of Evolution