1. Population Evolution ch. 23
One misconception is that organisms evolve, in the Darwinian sense, during their lifetimes
Natural selection acts on individuals, but only _____________________
______________________ in populations contribute to evolution
_____________________ is a change in allele frequencies in a population over generations
populations evolve
Genetic variations
Microevolution
mutation and sexual reproduction
Two processes, ____________________________, produce the variation in gene pools that contributes to differences among individuals
Variation
__________________ in individual genotype leads to variation in individual phenotype
Not all _______________ variation is heritable
Natural selection can only act on _____________with a genetic component
phenotypic
variation

2. Fig. 23-1
Figure 23.1 Is this finch evolving by natural selection?

3. Fig. 23-2a
(a)
Figure 23.2 Nonheritable variation

4. Fig. 23-2b
(b)
Figure 23.2 Nonheritable variation

5. Variation Within a Population
Both discrete and quantitative characters contribute to variation within a population
___________________ can be classified on an either-or basis
___________________ vary along a continuum within a population
Discrete characters
Quantitative characters
Population geneticists measure polymorphisms in a population by determining the ____________________________ at the gene and molecular levels
amount of heterozygosity
Variation Between Populations
geographic variation
Most species exhibit __________________, differences between gene pools of separate populations or population subgroups
Cline - __________________________________________________
a graded change in some trait along a geographic axis

6. Fig. 23-3
Geographic variation in isolated mouse populations on Madeira 1
2.4
3.14
5.18 6
7.15
8.11
9.12
10.16
13.17 19 XX 1
2.19
3.8
4.16
5.14
6.7
Figure 23.3 Geographic variation in isolated mouse populations on Madeira
9.10
11.12
13.17
15.18 XX

7. Figure 23.8 Clinal variation in a plant
variations within
a population
geographic variation

8. Ldh-B b allele frequency
Fig. 23-4
A cline determined by temperature
1.0
0.8
0.6
Ldh-B b allele frequency
0.4
0.2
Figure 23.4 A cline determined by temperature 46 44 42 40 38 36 34 32 30
Latitude (°N)
Maine
Cold (6°C)
Georgia
Warm (21°C)

9. Mutation
_______________are changes in the nucleotide sequence of DNA
Mutations cause new ___________________ to arise
Only mutations in cells that produce ______________ can be passed to offspring
Mutations
genes and alleles
gametes
A ____________________ is a change in one base in a gene
point mutation
The effects of point mutations can vary:
Mutations in noncoding regions of DNA are often ______________
harmless
Chromosomal mutations that delete, disrupt, or rearrange many loci are typically ________________
Duplication of large chromosome segments is usually ______________
harmful
harmful
animals and plants
Mutation rates are low in _______________________________
The average is about one mutation in every 100,000 genes per generation
Mutations rates are often ______________ in prokaryotes and ____________ in viruses
lower
higher

10. Sexual Reproduction
_____________________ can shuffle existing alleles into new combinations
In organisms that reproduce _____________, ____________________ _________________ is more important than ___________ in producing the genetic differences that make adaptation possible
Sexual reproduction
sexually
recombination
of alleles
mutation
The Hardy-Weinberg equation can be used to test whether a population is evolving
A _________________ is a localized group of individuals capable of interbreeding and producing _____________ offspring
A _______________ consists of all the alleles for all loci in a population
A locus is fixed if all individuals in a population are homozygous for the same allele
population
fertile
gene pool

11. One species, two populations
Fig. 23-5
One species, two populations
Porcupine herd
MAP
AREA
CANADA
ALASKA
Beaufort Sea
NORTHWEST
TERRITORIES
Porcupine
herd range
Figure 23.5 One species, two populations
Fortymile
herd range
ALASKA
YUKON
Fortymile herd

12. p + q = 1 Hardy-Weinberg Principle
The frequency of an allele in a population can be calculated
For ___________ organisms, the total number of alleles at a locus is the total number of individuals _______
diploid
x 2
p and q
By convention, if there are 2 alleles at a locus, _______________ are used to represent their _________________
The frequency of all alleles in a population will add up to 1
For example
frequencies
p + q = 1
The Hardy-Weinberg principle describes a population that is ____ evolving
If a population does ____________ the criteria of the Hardy-Weinberg principle, it can be concluded that the population is ____________
NOT
not meet
evolving

13. Alleles p + q = 1 p=A, q=a p2 + 2pq + q2 = 1 AA Aa aa no migration
Hardy Weinbeg Equation:
Requirements for Hardy Weinberg Equilibrium: 5.
p + q = 1 p=A, q=a
p2 + 2pq + q2 = 1 AA Aa aa
no migration
no natural selection
no net mutations
large population
random mating

14. Hardy-Weinberg Equilibrium
The Hardy-Weinberg principle states that _______________ of ____________________________ in a population remain constant from _____________________________
In a given population where gametes contribute to the next generation randomly, allele frequencies will ________ change
Mendelian inheritance ______________ genetic variation in a population
frequencies
alleles and genotypes
generation to generation
NOT
preserves
Hardy-Weinberg equilibrium describes the constant frequency of alleles in such a gene pool
If p and q represent the relative frequencies of the only two possible alleles in a population at a particular locus, then
where p2 and q2 represent the frequencies of the _____________ genotypes
2pq represents the frequency of the _________________ genotype
p2 + 2pq + q2 = 1
homozygous
heterozygous

15. Conditions for Hardy-Weinberg Equilibrium
The Hardy-Weinberg theorem describes a _______________ population
In real populations, allele and genotype frequencies ____change over time
hypothetical DO
The five conditions for nonevolving populations are rarely met in nature:
__________________________
No mutations
Random mating
No natural selection
Extremely large population size
No gene flow
Natural populations can evolve at some loci, while being in Hardy-Weinberg equilibrium at other loci

16. Natural selection, genetic drift, and gene flow can alter allele frequencies in a population
Three major factors alter allele frequencies and bring about most evolutionary change:
_____________________
Natural selection
Genetic drift
(small populations)
Gene flow
(migration)
Natural Selection
Differential success in reproduction results in certain alleles being passed to the next generation in ______________________
greater proportions

17. Genetic Drift
The smaller a sample, the greater the chance of deviation from a predicted result
__________________ describes how allele frequencies fluctuate unpredictably from one generation to the next
Genetic drift tends to __________ genetic variation through _______ of alleles
Genetic drift
reduce
loss
The ________________ occurs when a few individuals become isolated from a larger population
Allele frequencies in the small founder population can be different from those in the larger parent population
founder effect
The ________________ is a sudden reduction in population size due to a change in the environment
The resulting gene pool may no longer be reflective of the original population’s gene pool
If the population remains small, it may be further affected by genetic drift
bottleneck effect

18. - floods - volcanoes - ice ages not in Hardy Weinberg equilibrium
Genetic Drift
not in Hardy Weinberg
equilibrium
p and q are not staying
constant throughout the
generations
Bottleneck Effect:
the population undergoes a
dramatic decrease in size
- floods
- volcanoes
- ice ages

19. Case Study: Impact of Genetic Drift on the Greater Prairie Chicken
Loss of prairie habitat caused a severe reduction in the population of greater prairie chickens in Illinois. The surviving birds had low levels of genetic variation, and only 50% of their eggs hatched
Fig a
Pre-bottleneck
(Illinois, 1820)
Post-bottleneck
(Illinois, 1993)
Range
of greater
prairie
chicken
Figure Bottleneck effect and reduction of genetic variation
Researchers used DNA from museum specimens to compare genetic variation in the population before and after the bottleneck
The results showed a loss of alleles at several loci
Researchers introduced greater prairie chickens from population in other states and were successful in introducing new alleles and increasing the egg hatch rate to 90%

20. Effects of Genetic Drift: A Summary
Genetic drift is significant in _________________________
Genetic drift causes allele frequencies to change at ____________
Genetic drift can lead to a loss of _______________ within populations
Genetic drift can cause harmful alleles to become ___________
small populations
random
genetic variation
fixed
Gene Flow
movement
Gene flow consists of the ______________ of alleles among populations
Alleles can be transferred through the movement of fertile individuals or gametes (for example, pollen)
Gene flow tends to __________________ between populations over time
Gene flow is more likely than mutation to alter allele frequencies directly
reduce differences

21. Fig
Gene Flow
Figure Gene flow and human evolution

22. Gene flow can decrease the fitness of a population70
NON-
MINE
SOIL
MINE
SOIL
NON-
MINE
SOIL 60 50
Prevailing wind direction
Index of copper tolerance 40 30 20 10 20 20 20 40 60 80
100
120
140
160
Distance from mine edge (meters)
Figure Gene flow and selection
In bent grass, alleles for copper tolerance are beneficial in populations near copper mines, but harmful to populations in other soils
Windblown pollen moves these alleles between populations
The movement of unfavorable alleles into a population results in a decrease in fit between organism and environment

23. Only natural selection consistently results in ______________________
Natural selection is the only mechanism that consistently causes adaptive evolution
Only natural selection consistently results in ______________________
adaptive evolution
Natural selection brings about adaptive evolution by acting on an organism’s ______________
phenotype
Relative Fitness
The phrases “struggle for existence” and “survival of the fittest” are misleading as they imply direct competition among individuals
Reproductive success is generally more subtle and depends on many factors
__________________ is the contribution an individual makes to the __________________ of the next generation, relative to the contributions of other individuals
Selection favors certain ______________ by acting on the ____________ of certain organisms
Relative fitness
gene pool
genotypes
phenotypes

24. Directional, Disruptive, and Stabilizing Selection
Three modes of selection:
_____________________ favors individuals at one end of the phenotypic range
_____________________ favors individuals at both extremes of the phenotypic range
_____________________ favors intermediate variants and acts against extreme phenotypes
Directional selection
Disruptive selection
Stabilizing selection

25. Frequency of individuals
Original population
Frequency of individuals
Phenotypes (fur color)
Original
population
Evolved
population
Figure Modes of selection
(a) Directional selection
(b) Disruptive selection
(c) Stabilizing selection

26. The Key Role of Natural Selection in Adaptive Evolution
Natural selection increases the frequencies of alleles that enhance _______________________________
Adaptive evolution occurs as the match between an organism and its environment _________________
survival and reproduction
increases
Because the environment can change, adaptive evolution is a _______________ process
Genetic drift and gene flow do not consistently lead ______________ evolution as they can increase or decrease the match between an organism and its environment
continuous
to adaptive

27. Movable bones (b) Movable jaw bones in snakes Examples of adaptations
Fig b
Movable bones
Examples of adaptations
Figure Examples of adaptations
(b) Movable jaw
bones in
snakes

28. (a) Color-changing ability in cuttlefish
Fig a
Figure Examples of adaptations
(a) Color-changing ability in cuttlefish

29. Sexual Selection
Sexual selection is natural selection for _____________________
It can result in ___________________, marked differences between the sexes in secondary sexual characteristics
mating success
sexual dimorphism
___________________ is _______________ among individuals of one sex (often males) for mates of the opposite sex
_______________________, often called mate choice, occurs when individuals of one sex (usually females) are choosy in selecting their mates
Male showiness due to mate choice can increase a male’s chances of attracting a female, while decreasing his chances of survival
Intrasexual selection
competition
Intersexual selection

30. Fig
Figure Sexual dimorphism and sexual selection

33. The distinctive feature of this monkey is their protruding nose
The distinctive feature of this monkey is their protruding nose. It’s not defined about the purpose of the large nose, but it has been determined as the result of sexual selection. The female Proboscis Monkey prefers big-nosed male, thus propagating the trait.

34. ► Heterozygote Advantage ► Frequency-Dependent Selection
The Preservation of Genetic Variation
Various mechanisms help to preserve genetic variation in a population
► Balancing Selection
Balancing selection occurs when natural selection maintains _________ frequencies of two or more ________________________ in a population
stable
phenotypic forms
► Diploidy
Diploidy maintains genetic variation in the form of ___________________ alleles
hidden recessive
► Heterozygote Advantage
Heterozygote advantage occurs when heterozygotes have a ___________ fitness than do both homozygotes
Natural selection will tend to maintain two or more alleles at that locus
The sickle-cell allele causes mutations in hemoglobin but also confers malaria resistance
higher
► Frequency-Dependent Selection
In frequency-dependent selection, the fitness of a phenotype _____________ if it becomes ________________ in the population
Selection can favor whichever phenotype is _________________ in a population
declines
too common
less common

35. Plasmodium falciparum (a parasitic unicellular eukaryote) 7.5–10.0%
Fig
Frequencies of the
sickle-cell allele
0–2.5%
Figure Mapping malaria and the sickle-cell allele
2.5–5.0%
5.0–7.5%
Distribution of
malaria caused by
Plasmodium falciparum
(a parasitic unicellular eukaryote)
7.5–10.0%
10.0–12.5%
>12.5%

36. “left-mouthed” individuals
Fig
Frequency-dependent selection in scale-eating fish (Perissodus microlepis)
“Right-mouthed”
1.0
“Left-mouthed”
“left-mouthed” individuals
Frequency of
0.5
Figure Frequency-dependent selection in scale-eating fish (Perissodus microlepis)
1981
’82
’83
’84
’85
’86
’87
’88
’89
’90
Sample year