Download Evolution II

Chapter 16
The Evolution II
PowerPoint TextEdit Art Slides for
Biology, Seventh Edition
Neil Campbell and Jane Reece
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Figure 23.1 Variation in a natural population
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Figure 23.2 Individuals are selected; populations
evolve
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Populations as the Units of Evolution
• A population
– Is a group of individuals of the same species
living in the same area at the same time
– Is the smallest biological unit that can evolve
Figure 13.16
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Figure 23.3 One species, two populations
MAP
AREA
•
Fairbanks
Fortymile
herd range
•
Whitehorse
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Analyzing Gene Pools
• The gene pool
– Consists of all alleles of all individuals making
up a population
– Occur in certain frequencies (allele
frequencies)
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• The Hardy-Weinberg formula
– Is a mathematical representation of a gene
pool
– Determines the allele frequency in a population
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Microevolution as Change in a Gene Pool
• Hardy-Weinberg equilibrium
– Describes a nonevolving population that is in
genetic equilibrium
– Can be used to determine whether a
population is evolving
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Microevolution as Change in a Gene Pool
• A population MUST meet these conditions in
order for it to NOT evolve
– Very large population size
– No immigration or emigration
– Random mating
– No mutations
– No natural selection
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MECHANISMS OF MICROEVOLUTION
• Any deviation from these conditions will cause
microevolution to occur
• So these are the causes of microevolution
– Genetic drift
– Gene flow
– Nonrandom mating
– Mutations
– Natural selection
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Only 5 of
10 plants
leave
offspring
Generation 1
p (frequency of R) = 0.7
q (frequency of r) = 0.3
Only 2 of
10 plants
leave
offspring
Generation 2
p = 0.5
q = 0.5
Generation 3
p = 1.0
q = 0.0
Figure 13.20
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The Bottleneck Effect
• The bottleneck effect
– Is an example of genetic drift
– Results from a drastic reduction in population
size
Original
population
Bottlenecking
event
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Surviving
population
Figure 13.21
The Founder Effect
• The founder effect
– Is genetic drift in a new
colony
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Genetic Drift and Hereditary Disorders in Human
Populations
• The founder effect
– Explains the relatively high frequency of certain
inherited disorders among some populations
Figure 13.23
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Gene Flow
• Gene flow
– Is genetic exchange
with another
population
– Tends to reduce
genetic differences
between populations
Figure 13.24
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Nonrandom Mating
• Choosing a mate means that not every
individual will pass on their traits to the next
generation
• Only certain genes are passed along to the
offspring
Figure 13.24
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Mutations
• Mutations
– Are changes in an organism’s DNA
– Alone do not have much effect on a large
population
– Can have significant cumulative effects on a
population
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Animal behavior can also be affected by evolution
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