1. Evidence for Evolution
Direct Observation
Fossil Record
Homology
Biogeography

2. Application of Information
Graph the data found in the table
Examine the graph and hypothesize why the percentage of mosquitoes resistant to DDT rose rapidly
Suggest an explanation for the global spread of DDT resistance

3. Individuals do not evolve, populations do.
There was a population of 1200 ground finches that was wiped to 180 during a period of drought. Those that survived had larger, deeper beaks than those that died. Scientists observed that soft seeds, which finches normally eat, were in short supply, whereas hard ones were more plentiful. In the next generation of finches, the average beak size was bigger.

4. Fig. 23-1

5. Individuals do not evolve, populations do.
In a paragraph, describe the statement above. Use examples to help support your answer. You may use the finch example if you choose, or you may come up with another one.

6. Chapter 23: The Evolution of Populations
Ms. Klinkhachorn
March 21, 2011
AP Biology

7. Microevolution
Microevolution = the change in allele frequencies over generations
Example:
The allele for larger beak became more frequent after the drought selected for finches with this type of beak
The allele for smaller beak became less frequent since these finches would have a hard time surviving.

8. Ldh-B b allele frequency
Fig. 23-4
1.0
0.8
0.6
Ldh-B b allele frequency
0.4
0.2 46 44 42 40 38 36 34 32 30
Latitude (°N)
Maine
Cold (6°C)
Georgia
Warm (21°C)

9. What makes evolution possible?
Genetic variation!
If there are no differences in the gene pool, there is nothing for natural selection to pick

10. What causes genetic variation?
Mutation (chromosomal and DNA)
Source of new alleles
More harmful, but can occasionally be beneficial
Sexual Reproduction
Every individual gets a unique combination
Crossing over
Independent assortment
Fertilization

11. Background Info
Population = a group of individuals of the same species that live in the same area and mate with one another
Gene Pool = all of the genes of a population of organisms
Fixed population

12. Hardy – Weinberg Principle
HW Principle says that the frequencies of alleles and genotypes in a population will remain constant from generation to generation
A gene pool in this state is said to be in Hardy-Weinberg equilibrium
Use this principle to help us figure out if a population is evolving or not

13. Conditions for Hardy – Weinberg
No mutations
Random mating
No natural selection
Large population size
No gene flow (no immigration and emigration)
If these conditions change, evolution can occur and you are no longer in HW equilibrium

14. Hardy-Weinberg Equation
If p and q represent the relative frequencies of the only two possible alleles in a population at a particular locus, then
p2 + 2pq + q2 = 1
where p2 and q2 represent the frequencies of the homozygous genotypes and 2pq represents the frequency of the heterozygous genotype
p is usually the dominant allele, q is recessive

15. Alleles in the population Frequencies of alleles
Fig. 23-6
Alleles in the population
Frequencies of alleles
Gametes produced
p = frequency of
Each egg:
Each sperm:
CR allele = 0.8
q = frequency of
80%
chance
20%
chance
80%
chance
20%
chance
CW allele = 0.2
Figure 23.6 Selecting alleles at random from a gene pool

16. 80% CR ( p = 0.8) 20% CW (q = 0.2) Sperm CR (80%) Eggs CW (20%) CR CW
Fig
80% CR ( p = 0.8)
20% CW (q = 0.2)
Sperm CR
(80%) CW
(20%) CR
(80%)
Figure 23.7 The Hardy-Weinberg principle
Eggs
64% ( p2)
CRCR
16% ( pq)
CRCW
4% (q2)
CW CW
16% (qp)
CRCW CW
(20%)

17. Example Problem
Suppose in a plant population that red flowers (R) are 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?

18. Application of HW The occurrence of PKU is 1 per 10,000 births
q2 =
q = 0.01
The frequency of normal alleles is
p = 1 – q = 1 – 0.01 = 0.99
The frequency of carriers is
2pq = 2 x 0.99 x 0.01 =
or approximately 2% of the U.S. population

19. Practice Problem
Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all butterflies are white.
Calculate the following:
The percentage of butterflies in the population that are heterozygous.
The frequency of homozygous dominant individuals
If there are 200 butterflies, how many are brown?

20. Practice Problem
After graduation, you and 19 of your friends charter a plane to go on a round-the-world tour. Unfortunately, you all crash land (safely) on a deserted island. No one finds you and you start a new population totally isolated from the rest of the world. Two of your friends are carriers for cystic fibrosis.
Assuming that the frequency of this allele does not change as the population grows, what will be the incidence of cystic fibrosis on your island?

21. Allelic Frequencies Can Be Altered
Three major factors alter allele frequencies and bring about most evolutionary change:
Natural selection
Genetic drift
Gene flow

22. Natural Selection

23. Genetic Drift
Genetic drift = chance events can cause allele frequencies to fluctuate unpredictably, especially in small populations

24. Generation 1 p (frequency of CR) = 0.7 q (frequency of CW ) = 0.3
Fig
CR CR
CR CR
CR CW
CW CW
CR CR
CR CW
CR CR
CR CW
CR CR
CR CW
Generation 1
p (frequency of CR) = 0.7
q (frequency of CW ) = 0.3

25. Generation 1 Generation 2 p (frequency of CR) = 0.7 p = 0.5
Fig
CR CR
CR CR
CW CW
CR CR
CR CW
CR CW
CW CW
CR CR
CR CR
CW CW
CR CW
CR CW
CR CR
CR CW
CW CW
CR CR
CR CR
CR CW
CR CW
CR CW
Generation 1
Generation 2
p (frequency of CR) = 0.7
p = 0.5
q (frequency of CW ) = 0.3
q = 0.5

26. Generation 1 Generation 2 Generation 3 p (frequency of CR) = 0.7
Fig
CR CR
CR CR
CW CW
CR CR
CR CR
CR CW
CR CW
CR CR
CR CR
CW CW
CR CR
CR CR
CR CR
CW CW
CR CR
CR CW
CR CW
CR CR
CR CR
CR CR
CR CW
CW CW
CR CR
CR CR
CR CR
CR CW
CR CW
CR CW
CR CR
CR CR
Generation 1
Generation 2
Generation 3
p (frequency of CR) = 0.7
p = 0.5
p = 1.0
q (frequency of CW ) = 0.3
q = 0.5
q = 0.0

27. Types of Genetic Drift Founder Effect Bottleneck Effect
A few individuals in a population become isolated from the rest of the population and FOUND a new population
Bottleneck Effect
Caused by drastic reduction in population size because of fire or flood (catastrophe)

28. Original population Bottlenecking event Surviving population
Fig. 23-9
Original
population
Bottlenecking
event
Surviving
population

29. Gene Flow
Gene flow = transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes
Reduce the genetic differences across different population
Could end up combining the populations and make a common gene pool

30. Fig

32. Natural Selection and Relative Fitness
Relative fitness = the contribution an individual makes to the gene pool of the next generation, relative to the contribution of other individuals
Depends on adaptations
More adaptations there are, the more fit you are

33. Mechanism of Natural Selection

34. Normal Distribution of Traits

35. Types of Natural Selection
Natural selection changes the allelic frequency, depending on how the phenotypes are favored in the environment
Directional
Disruptive
Stabilizing

36. Frequency of individuals
Fig
Original population
Frequency of individuals
Phenotypes (fur color)
Original
population
Evolved
population
(a) Directional selection
(b) Disruptive selection
(c) Stabilizing selection

37. Directional Selection
Conditions favor individuals exhibiting an extreme of a phenotypic range (shift the curve to the right or the left
Most commonly occurs when:
The environment changes (drought, fire)
Migration

38. Directional Selection

39. Frequency of individuals
Fig a
Original population
Frequency of individuals
Phenotypes (fur color)
Original population
Evolved population
(a) Directional selection

40. Examples: Directional Selection
Peppered Moths and the Industrial Revolution
When the trees were light colored (before), the moths that were light colored were favored
When the trees were darkened (by the pollution), the moths that were darker were favored
See regular shifts

41. Examples: Directional Selection
Bird beaks on an island

42. Disruptive Selection
Conditions favor individuals at BOTH extremes of the phenotype range
Example:
Birds with small beaks and birds with really big beaks are specialized
Birds with medium beaks are inefficient

43. Frequency of individuals
Fig b
Original population
Frequency of individuals
Phenotypes (fur color)
Evolved population
(b) Disruptive selection

44. Examples: Disruptive Selection
Harbor Seals
Smaller seals are faster and more agile. They can hunt small, quick prey
Larger seals are powerful and can get bigger prey
Medium sized can’t do either well

45. Stabilizing Selection
Conditions favor the intermediate phenotypes
Most common type of selection

46. Frequency of individuals
Fig c
Original population
Frequency of individuals
Phenotypes (fur color)
Evolved population
(c) Stabilizing selection

47. Example: Stabilizing Selection
Weight of newborn babies is typically between 6 and 9 lbs
Too small: lose heat, get sick more easily
Too big: harder to deliver during childbirth

48. Example: Stabilizing Selection
Mountain Goats and Leg Length
Short legs: not as agile, can’t move as easily
Long legs: don’t have good balance

49. Quick Write What is evolution?
Describe the mechanism and how, depending on the environment, the selection can vary.
Give examples of how genetic variation can enter a population at the molecular level AND at the population level.