Download 1 Populations are the units of evolution The gene pool of a

Populations are the units of evolution
– A population
•
Is a group of individuals of the same species living in the
same place at the same time
– A species is a group of populations
•
Whose individuals can interbreed and produce fertile
offspring
– Population genetics
•
Studies how populations change genetically over time
•
A gene pool is the total collection of genes in a population
at any one time
The gene pool of a nonevolving population remains constant
over the generations
In a nonevolving population
The shuffling of alleles that accompanies sexual reproduction
does not alter the genetic makeup of the population
Figure 13.7A
Webbing
No webbing
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Hardy-Weinberg equilibrium
– States that the shuffling of genes during sexual reproduction does not
alter the proportions of different alleles in a gene pool
Figure 13.7A
Webbing
No webbing
Phenotypes
Genotypes
WW
Number of animals 320
(total = 500)
320 = 0.64
Genotype frequencies
500
Number of alleles
in gene pool
(total = 1,000)
Allele frequencies
Figure 13.7B
640 W
Ww
ww
160
20
160 = 0.32
500
160 W + 160 w
800 = 0.8 W
1,000
20 = 0.04
500
40 w
200 = 0.2 w
1,000
The Hardy-Weinberg equation is useful in public health
science
– Public health scientists use the Hardy-Weinberg equation
•
To estimate frequencies of disease-causing alleles in the
human population
2
The Hardy-Weinberg equation is useful in public health
science
– Public health scientists use the Hardy-Weinberg equation
•
To estimate frequencies of disease-causing alleles in the
human population
3
In addition to natural selection, both genetic drift and gene
flow can contribute to evolution
– Genetic drift
•
Is a change in the gene pool of a population due to chance
•
Can alter allele frequencies in a population
•
Can cause the bottleneck effect or the founder effect
Original
population
Bottlenecking
event
Surviving
population
In addition to natural selection, genetic drift and gene flow
can contribute to evolution
– Genetic drift
•
Is a change in the gene pool of a population due to chance
•
Can alter allele frequencies in a population
•
Can cause the bottleneck effect or the founder effect
– Gene flow
•
Is the movement of individuals or gametes between populations
•
Can alter allele frequencies in a population
4
In addition to natural selection, genetic drift and gene flow
can contribute to evolution
– Genetic drift
•
Is a change in the gene pool of a population due to chance
•
Can alter allele frequencies in a population
•
Can cause the bottleneck effect or the founder effect
– Gene flow
•
Is the movement of individuals or gametes between populations
•
Can alter allele frequencies in a population
– Natural selection
•
Leads to differential reproductive success in a population
•
Can alter allele frequencies in a population
Endangered species often have low genetic variability
– May reduce the capacity of endangered species to survive as
humans continue to alter the environment
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Genetic variation is extensive in most populations
– Many populations exhibit polymorphism
•
Different forms of phenotypic characteristics
Figure 13.11
The evolution of antibiotic resistance in bacteria is a serious
public health concern
– The excessive use of antibiotics
•
Is leading to the evolution of antibiotic-resistant bacteria
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The origin of species is the source of biological diversity
–Speciation, potentially in conjunction with extinction, is at the focal
point of evolution
Figure 14.1
What is a species?
– Similarities between some species and variation within a species can
make defining species difficult
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The Biological Species Concept
–The biological species concept defines a species as
•A population or group of populations whose members can
interbreed and produce fertile offspring
The Biological Species Concept
–The biological species concept defines a species as
•A population or group of populations whose members can
interbreed and produce fertile offspring
Figure 14.3D
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The Biological Species Concept
–The biological species concept defines a species as
•A population or group of populations whose members can
interbreed and produce fertile offspring
The Biological Species Concept
–The biological species concept defines a species as
•A population or group of populations whose members can
interbreed and produce fertile offspring
Other Species Concepts
–The morphological species concept
•Classifies organisms based on observable phenotypic traits
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The Biological Species Concept
–The biological species concept defines a species as
•A population or group of populations whose members can
interbreed and produce fertile offspring
Other Species Concepts
–The morphological species concept
•Classifies organisms based on observable phenotypic traits
–The ecological species concept
•Defines a species by its ecological role
–The phylogenetic species concept
•Defines a species as a set of organisms representing a specific
evolutionary lineage
The origin of species is the source of biological diversity
–Speciation, potentially in conjunction with extinction, is at the focal
point of evolution
Figure 14.1
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Reproductive barriers keep species separate
– Reproductive barriers
• Serve to isolate a species’ gene pool and prevent interbreeding
• Are categorized as prezygotic or postzygotic
Table 14.3
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Postzygotic barriers
– Operate after hybrid zygotes are formed
– One postzygotic barrier is hybrid sterility
• Where hybrid offspring between two species are sterile and
therefore cannot mate
Figure 14.3D
Table 14.3
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Speciation
A. harrisi
A. leucurus
Figure 14.4
Speciation
A. harrisi
A. leucurus
Figure 14.4
A population is geographically divided, and new species often
evolve
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Table 14.3
Evolution
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Is evolution goal directed?
Is evolution goal directed?
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Are Birds Really Dinosaurs with Feathers?
– Did birds evolve from dinosaurs?
– Evolutionary biologists
• Have been pondering this question for decades
Evolution
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Mass extinctions were followed by diversification of life-forms
– Mass extinctions
• Occurred at the end of the Permian and Cretaceous periods
Great periods of adaptive radiation
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One early theory suggested that as dinosaurs evolved into
larger and larger creatures they simply became too stupid
to survive.
The Cretaceous extinction, which included the dinosaurs
• May have been caused by an asteroid
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The Cretaceous extinction, which included the dinosaurs
•Berkeley geologist named Walter Alvarez.
•a slender layer of red clay between the Late Cretaceous rock and the Paleocene
rock lying on top of it.
•contained thirty times the amount of the rare element iridium
The Cretaceous extinction, which included the dinosaurs
• May have been caused by an asteroid
•a collision between the earth and a gigantic asteroid rich in iridium
•the force of thousands of atomic bombs
•A dust cloud high into the sky.
•This cloud would block out nearly all of the sunlight, creating a long, cold,
unnatural winter, drastically changing the climate for years to come.
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The Cretaceous extinction, which included the dinosaurs
• May have been caused by an asteroid
•a collision between the earth and a gigantic asteroid rich in iridium
•the force of thousands of atomic bombs
•A dust cloud high into the sky.
•This cloud would block out nearly all of the sunlight, creating a long, cold,
unnatural winter, drastically changing the climate for years to come.
•The few plants and animals that managed to survive, such as crocodiles and
early mammals, became the new rulers of a world without dinosaurs.
Other theories of extinction blame drastic changes in the environment.
•
Geological shifts may have caused critical changes in the earth's
atmosphere and consequentially the weather.
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The formation of Pangaea
• Altered habitats and triggered extinctions
The separation of the continents
• Affected the distribution and diversification of organisms
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