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Mader: Biology 8th Ed.
Population Genetics
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Genetic diversity in populations changes
over generations
Forces that cause populations to evolve
Allele and genotype frequencies over
generations
Mader: Biology 8th Ed.
Microevolution
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Change in gene frequencies between
populations of a species over time
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Hardy-Weinberg Equilibrium
Stable, non-evolving population
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Mader: Biology 8th Ed.
The nitty-gritty: p292 of text
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Random mating
No selection (no reproductive advantages)
No mutation
No migration
Large population
Mader: Biology 8th Ed.
Migration aka GENE FLOW
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Amount depends on:
– Distance between populations
– Ability of individuals/gametes to move
between populations
– behavior
No migration can result in reproductive
isolation
Mader: Biology 8th Ed.
Genetic Drift: A result of small populations
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Chance events alter the gene pool
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Bottleneck effect
Founder effect
High level of inbreeding – loss of diversity in
the population
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Mader: Biology 8th Ed.
Mader: Biology 8th Ed.
How do we define a “species”?
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Morphological species
– Cryptic species
Evolutionary species (fossils)
Biological species
Mader: Biology 8th Ed.
Reproductive Isolation
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Incapable of interbreeding…
– Formation of new species…
SPECIATION
Mader: Biology 8th Ed.
Speciation
The splitting of one species into two or more
species.
OR
The transformation of one species into a
new species over time.
Mader: Biology 8th Ed.
Modes of Speciation
1.
Allopatric Speciation (Greek, different
fatherland)—a population forms a new
species while geographically separated
from its parent population.
reproductive isolation occurs.
Examples: squirrels on either side of the
Grand Canyon; pupfish in springs in the
deserts of California and Nevada; adaptive
radiation in island chains.
Mader: Biology 8th Ed.
Modes of Speciation continued
2. Sympatric Speciation (Greek, together,
fatherland)—a population develops two or
more reproductively isolated groups without
prior geographic isolation.
Usually a mutation erects a reproductive
barrier between the mutants and the parent
population.
Best evidence is found among plants
where it can occur by means of polyploidy or
by hybridization between two species
followed by doubling of the chromosome
number. These new plants can no longer
reproduce with the parent species.
Mader: Biology 8th Ed.
Figure 24.6 Two modes of speciation
Mader: Biology 8th Ed.
Figure 24.7 Allopatric speciation of squirrels in the Grand Canyon
Mader: Biology 8th Ed.
Figure 23.9 Geographic variation between isolated populations of house mice
Mader: Biology 8th Ed.
Figure 24.8 Has speciation occurred during geographic isolation?
Mader: Biology 8th Ed.
Figure 24.13 Sympatric speciation by autopolyploidy in plants
Mader: Biology 8th Ed.
Figure 24.15 One mechanism for allopolyploid speciation in plants
Mader: Biology 8th Ed.
Adaptive Radiation
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Is an example of allopatric speciation.
The rapid development from a single ancestral
species of many new species, which have spread
out and become adapted to various ways of life.
--as the parent population increases in size,
daughter populations are subjected to the founder
effect and the process of natural selection.
--Examples: 13 species of Galapagos finches
20+ species of Hawaiian
honeycreeper
500 species of Drosophila in Hawaii
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.
Types of evolution
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Divergent
Parallel
Convergent
Mader: Biology 8th Ed.
Rates of Evolution
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.