2. Topics: 1) Genetic variation
2) Fitness
3) Adaptation

3. But how is variation generated and maintained?

4. Mutation generates variation
Eye Color Gene
DNA Code
Result b
CATGAT b
mutation
CATGTT B

5. Sexual recombination generates variation
Two ways:
1) Crossing-over
2) Random segregation

6. Crossing-over

7. Two homologous chromosomes

8. Two homologous chromosomes
Crossing over can occur

9. switch Two homologous chromosomes
Result: a change in the gene combinations of homologous chromosomes

10. Segregation of Homologs

11. Sperm or eggs

12. Variation can be maintained by …
Diploidy
Balanced polymorphism
a) Frequency-dependent selection
b)Heterozygote advantage
3) Neutral variation

13. Variation can be maintained by …
Diploidy
“B” is better in an environment,
“b” can be preserved in the
heterozygote condition (I.e., Bb)

14. Balanced polymorphism
**Heterozygote advantage**
Heterozygotes are better at surviving and leaving
Offspring than either homozygotes
For Example ..
Bb better than BB or bb

15. Balanced polymorphism
**Frequency-dependent selection
reproductive success depends on how common
an allele is in a population ….
if too common, the allele isn’t successful

16. 3) Neutral variation
Variation that at present, does not influence
reproductive success can be maintained because
selection does not act against it.

17. We reviewed the causes of microevolution
How genetic variation is
- generated
- maintained
Now ….

18. Focus: How adaptive evolution occurs through the action of natural selection operating on genetic variation

19. What is the currency of natural selection?

20. What is the currency of natural selection?
Fitness

21. Darwinian fitness – is the relative contribution an individual makes
to the gene pool of the next generation

22. Darwinian fitness – is the relative contribution an individual makes
to the gene pool of the next generation
Population geneticists are concerned with relative fitness –
the contribution of a genotype to the next generation
compared to the contributions of alternative genotypes
at the same locus

23. Natural Selection – is differential success in reproduction of individuals with different heritable characters within a given environment

24. Natural Selection – is differential success in reproduction of individuals with different heritable characters within a given environment
Consider the following …

25. Two genotypes/individual females

26. Two genotypes/individual females
Each genotype/individual leaves 2 descendants
Each genotype/individual leaves 1 descendant
Generation:

27. Reproductive potential?
Two genotypes/individuals
Which has the higher
Reproductive potential?
Generation:

28. Natural Selection isn’t a magical force, it is simply
Two genotypes/individuals
Natural Selection isn’t a
magical force, it is simply
differential reproductive
success in a given
environment!
Generation:

29. What else influences reproductive success besides NUMBER OF OFFSPRING produced?
Reproductive individuals

30. What else influences reproductive success besides NUMBER OF OFFSPRING produced?
individuals

31. Survival to reproductive age…

32. Survival to reproductive age…
Why might individuals not
survive to reproduce?

33. Survival to reproductive age…
Why might individuals not
survive to reproduce?
One reason - Predation

34. Habitat

35. 1) Individuals in the habitat
2) Variation among
individuals

36. A predator that uses
visual cues to find prey

37. Which color object is more visible on this background?

38. These two females leave equal numbers of offspring

39. Which offspring are more likely to be eaten?

40. These offspring
are more likely
to be eaten

41. These offspring are more likely to be eaten
Which offspring are more likely to survive to reproductive age?
These offspring
are more likely
to be eaten

43. In this example, the are more
likely than to survive to
reproductive age, thus they have a
greater opportunity to reproduce

44. But what if …

45. HABITAT

46. Which color object is more visible on this background?

47. Which offspring are more likely to be eaten?

48. Which offspring are more likely to be eaten?
Demonstrates the environmental
context of natural selection and
adaptation; and the relative nature
of fitness

49. How, let’s combine reproductive potential
and survival …

50. be more likely to survive to reproductive age?
Two genotypes/individuals
Which offspring would
be more likely to survive
to reproductive age?
Generation:

51. Two genotypes/individuals
Generation:

52. But what if …

53. be more likely to survive to reproductive age?
Two genotypes/individuals
Which offspring would
be more likely to survive
to reproductive age?
Generation:

54. This may be more successful! Two genotypes/individuals
Generation:

55. Take Home: The relative nature of fitness is
dependent upon the environmental context
within which genotypes/individuals reside

56. As of now, we have focused on Natural Selection and its currency, fitness,
But, what are the basic modes of selection?

57. Stabilizing selection – selection against the
extreme phenotypes/genotypes and in favor
of the intermediate phenotypes/genotypes

58. Frequency distribution
# of individuals
Blue Violet Red
Flower Color

59. Stabilizing Selection
# of individuals
Blue Violet Red
Flower Color

60. Stabilizing Selection
# of individuals
Blue Violet Red
Flower Color

61. Directional selection – selection for an
extreme/rare phenotype that results in a
unidirectional shift in character state

62. Directional Selection
# of individuals
Blue Violet Red
Flower Color

63. Directional Selection
# of individuals
Blue Violet Red
Flower Color

64. Diversifying selection – selection against
intermediate phenotypes, but not against the
extremes

65. Diversifying Selection
# of individuals
Blue Violet Red
Flower Color

66. Diversifying Selection
# of individuals
Blue Violet Red
Flower Color

67. Stabilizing, directional, and diversifying selection represent the basic modes of selection,
but what are some SPECIFIC TYPES OF SELECTION within Natural Selection?

68. But what are some SPECIFIC TYPES OF SELECTION within Natural Selection?

69. Ecological selection – selection for enhanced survival in a given environment

70. Sexual selection – selection for enhanced mating success based on variation in secondary sex characteristics

71. In many cases males and females differ not only in reproductive organs, but in traits related to obtaining mates. These differences are usually referred to as sexual dimorphism
For Example …

72. Male
Female

73. Male
Female

74. Female
Male

75. Female
Male

76. Sexual Selection can involve either or both:
1) Female choice (based on female picking a male to mate with because of his traits)
2) Male-male competition (based on males competing for resources like territories, and whom ever wins the territory, mates with the female)

77. Female Male What would be predicted to happen to male body depth
based on sexual selection?
Female
Male

78. Taller!

79. 100 c
Body Depth
(cm) b a c
Male b a

80. 100 c
Body Depth
(cm) b a
Sexual selection c
Male b a

81. What might be a problem with this?
100 c
Body Depth
(cm) b a
Sexual selection c
Male b a

82. Problem?
stream
Water flow

83. Water resistance swimming upstream.
Which male would be more successful at
swimming upstream?
stream
Water flow

84. Water resistance swimming upstream.
Which male would be more successful at
swimming upstream?
This one
stream
Water flow

85. Water resistance swimming upstream.
Which male would be more successful at
swimming upstream?
This one
stream
Water flow
What type of selection would
this be? Ecological or Sexual?

86. Ecological selection
100 c
Body Depth
(cm) b a
Sexual selection c
Male b a

87. Balance Ecological selection Ecological selection 100 100 Body Depth
(cm)
Sexual selection
Sexual selection
Male
Male

88. Why organisms aren’t perfect: (pg.442)
Organisms are locked into historical constraints
Adaptations are often compromises
Not all evolution is adaptive
Selection can only edit variation that exists

89. Theory of Evolution Today
Supporting Evidence
copyright cmassengale

90. copyright cmassengale
Homologous Structures
copyright cmassengale

92. Vestigial Structures

94. copyright cmassengale
Evidence for Evolution - Comparative Embryology
Similarities In Embryonic Development
copyright cmassengale

95. Similarities in DNA Sequence
copyright cmassengale

96. Evolution of pesticide resistance in response to selection
copyright cmassengale

97. copyright cmassengale
Evidence for Evolution – Evolution Observed
Evolution of drug-resistance in HIV
copyright cmassengale

98. Selection against small guppies results in an increase in average size
Evidence for Evolution – Evolution Observed
Selection against small guppies results in an increase in average size
copyright cmassengale

99. Evolutionary Time Scales
Macroevolution: Long time scale events that create and destroy species.
copyright cmassengale

100. Evolutionary Time Scales
Microevolution
Change in allele frequencies that occur over time within a populationo-generation) that change the genotypes and phenotypes of populations
copyright cmassengale

101. copyright cmassengale
Evidence of Evolution
Key Concept
Darwin Argued That Living Things Have Been Evolving On Earth For Millions of Years. Evidence For This Process Could Be Found In:
The Fossil Record
The Geographical Distribution of Living Species
Homologous Structures of Living Organisms
Similarities In Early Development
copyright cmassengale

102. Based upon the evidence of evolution and genetic phenotypes and genotypic trends, can we predict genetic populations?
YESS!!

103. Hardy Weinberg Principle
The Hardy–Weinberg principle, also known as the Hardy–Weinberg equilibrium, model, theorem, or law, states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences

104. Formula
Homozygotes
p2 + 2pq + q2 = 1 and p + q = 1 p = frequency of the dominant allele in the population q = frequency of the recessive allele in the population p2 = percentage of homozygous dominant individuals q2 = percentage of homozygous recessive individuals 2pq = percentage of heterozygous individuals Wat.
Heterozygotes

105. In a population with two alleles (B and b) for a particular locus, the frequency of B = 0.7
What is the frequency of heterozygotes if the population is in Hardy-Weinberg Equilibrium?

106. Remember:
(p+q)2= p+q=1
Heterozygotes
p 2 + 2pq +q 2 = 1
Homozygotes
We know: B = p = 0.7
We want to know: Frequency of Bb in population

107. Remember:
(p+q)2= p+q=1
p 2 + 2pq +q 2 = 1
We know: B = p = 0.7
We want to know: Frequency of Bb in population
What do we do first?

108. Remember:
(p+q)2= p+q=1
p 2 + 2pq +q 2 = 1
We know: B = p = 0.7
We want to know: Frequency of Bb in population
What do we do first?
plug into p+q= q=1
q=1-0.7
q=0.3

109. What do we do next? Remember: (p+q)2=1 p+q=1 p 2 + 2pq +q 2 = 1
We know: B = p = 0.7
We want to know: Frequency of Bb in population
Now we know: b = q = 0.3
What do we do next?

110. Remember:
(p+q)2= p+q=1
p 2 + 2pq +q 2 = 1
We know: B = p = 0.7
We want to know: Frequency of Bb in population
Now we know: b = q = 0.3
Plug into p 2 + 2pq +q 2 = 1
What was our question?

111. Remember:
(p+q)2= p+q=1
p 2 + 2pq +q 2 = 1
We know: B = p = 0.7
We want to know: Frequency of Bb in population
Now we know: b = q = 0.3
Plug into p 2 + 2pq +q 2 = 1
2pq = 2(0.7)(0.3) = 0.42

112. Remember:
(p+q)2= p+q=1
p 2 + 2pq +q 2 = 1
We know: B = p = 0.7
We want to know: Frequency of Bb in population
Now we know: b = q = 0.3
Plug into p 2 + 2pq +q 2 = 1
2pq = 2(0.7)(0.3) = 0.42
Our answer - Frequency of Bb in population is 42%

113. NEXT PROBLEM

114. If a population is in H-W equilibrium, and the frequency of the homozygous recessive genotype (bb) is 16%, what is the frequency of the dominant allele?

115. Remember:
(p+q)2= p+q=1
p2 + 2pq +q2 = 1
We know: bb = q2 = 0.16
We want to know: Frequency of B in population
What do we do first?

116. Remember:
(p+q)2= p+q=1
p2 + 2pq +q2 = 1
We know: bb = q2 = 0.16
We want to know: Frequency of B in population
What do we do first?
q2 =  0.16
q = 0.40

117. What do we do next? Remember: (p+q)2=1 p+q=1 p2 + 2pq +q2 = 1
We know: bb = q2 = 0.16
We want to know: Frequency of B in population
Now, we know q = 0.40
What do we do next?

118. Remember:
(p+q)2= p+q=1
p2 + 2pq +q2 = 1
We know: bb = q2 = 0.16
We want to know: Frequency of B in population
Now, we know q = 0.40
Plug into p+q=1
p+0.4=1
p=1-0.4
p= 0.6

119. Remember:
(p+q)2= p+q=1
p2 + 2pq +q2 = 1
We know: bb = q2 = 0.16
We want to know: Frequency of B in population
Now, we know q = 0.40
p = 0.6
Our answer - Frequency of B in population is 60%

120. What is the frequency of the B allele?
1) A population of rabbits may be brown (the dominant phenotype) or white (the recessive phenotype). Brown rabbits have the genotype BB or Bb. White rabbits have the genotype bb. The frequency of the BB genotype is .35.
What is the frequency of the B allele?
What is the frequency of the b allele?
What is the frequency of heterozygous rabbits?
2) A population of birds contains 16 animals with red tail feathers and 34 animals with blue tail feathers. Blue tail feathers are the dominant trait.
What is the frequency of the red allele?
What is the frequency of the blue allele?
What is the frequency of heterozygotes?
What is the frequency of birds homozygous for the blue allele?
48% , 59%, 41%
56%, 43%, 49%, 18%