Evolution of Populations Chapter 11. Genetic Variation Within Populations Variation and gene pools...
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- Slide 1
- Evolution of Populations Chapter 11
- Slide 2
- Genetic Variation Within Populations Variation and gene pools
Gene pool all genes present in a population Allele Frequency the
number of times an allele occurs in the gene pool, compared to
other alleles
- Slide 3
- Genetic Variation Within Populations In genetic terms,
evolution is any change in the relative frequency of alleles in a
population.
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- Genetic Variation Within Populations Scientists now recognize
two main sources of genetic variation Scientists now recognize two
main sources of genetic variation Mutations Mutations Recombination
Recombination
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- Genetic Variation Within Populations Mutations Any change in a
sequence of DNA Occurs Because: Problems with replication Exposure
to radiation or chemicals
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- Genetic Variation Within Populations Recombination Parents
alleles rearrange when forming gametes The 23 pairs of chromosomes
can produce 8.4 million different combinations!
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- Genetic Variation Within Populations Crossing Over Occurs
during meiosis Further increases genetic variation
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- Natural Selection In Populations Normal distribution Normal
distribution Highest frequency in middle and lowest at the extremes
Highest frequency in middle and lowest at the extremes Also
representative for allele freqencies Also representative for allele
freqencies
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- Natural Selection In Populations Microevolution Observable
changes in allelic frequencies Occurs in a single population 3 ways
Directional Stabilizing Disruptive
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- Natural Selection In Populations Directional Selection
Directional Selection Shift in phenotype to one extreme Shift in
phenotype to one extreme Mean also shifts Mean also shifts
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- Natural Selection In Populations Stabilizing Selection Norm is
selected for and becomes more common Ex. Gall Fly and
Goldenrod
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- Natural Selection In Populations Disruptive Selection
Disruptive Selection Selection for the extremes Selection for the
extremes Ex. Peppered moths Ex. Peppered moths
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- Natural Selection In Populations Single-gene and polygenic
traits Widows peak is a single gene trait a single gene with two
alleles Polygenic Traits are controlled by two or more genes This
means that a polygenic trait can have many possible genotypes ant
thus phenotypes.
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- 16-2 Evolution as Genetic Change Natural Selection on
Single-Gene Traits
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- Other Mechanisms of Evolution Gene Flow Gene Flow Some animals
move once they are able Some animals move once they are able When
the move into new population, their alleles become part of gene
pool When the move into new population, their alleles become part
of gene pool Occurs with movement between populations Occurs with
movement between populations Increases variation Increases
variation If less movement, the more different two species become
If less movement, the more different two species become
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- Other Mechanisms of Evolution Genetic Drift Random change in
allele frequency Bottleneck Effect Founder effect when allele
frequencies change because of migration
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- Other Mechanisms of Evolution Sexual Selection Females the
important factor in reproduction This makes females picky
Intrasexual selection Intersexual selection
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- Hardy-Weinberg Equilibrium Evolution vs. Genetic Equilibrium
Hardy-Weinberg principle genotype frequencies will stay constant
unless some factor changes the frequency Genetic Equilibrium when
allele frequencies remain constant
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- Hardy-Weinberg Equilibrium Five Conditions to Maintain
Equilibrium Random Mating Large Population No Movement into or out
of the population No Mutations No Natural Selection
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- Hardy-Weinberg Equilibrium Biologists can use an equation for
comparison purposes Biologists can use an equation for comparison
purposes p2 + 2pq + q 2 = 1 p = dominant alleles q = recessive
alleles
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- Hardy-Weinberg Equilibrium Five factors leading to evolution
Five factors leading to evolution Genetic drift Genetic drift Gene
flow Gene flow Sexual selection Sexual selection Natural selection
Natural selection Mutations Mutations
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- Speciation Through Isolation Reproductive Isolation members of
populations can no longer mate Mules or Hinnies Speciation - when
two species come from one existing species
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- Speciation Through Isolation Behavioral Isolation Two
populations will not breed because of differences in courtship
Fireflies
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- Speciation Through Isolation Geographical Isolation Rivers,
mountains, or bodies of water separate two populations Snapping
Shrimp and placental vs. marsupial mammals
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- Speciation Through Isolation Temporal Isolation Different
species mate at different times Times of day Times of year Trees
and plants
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- Patterns in Evolution Convergent Evolution evolution towards
similar characteristics in unrelated species Convergent Evolution
evolution towards similar characteristics in unrelated species
Analogous structures Analogous structures Bird and bat wings Bird
and bat wings
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- Patterns in Evolution Divergent Evolution closely related
species in different directions Results from adapting to different
environments Kit and Red Fox
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- Patterns in Evolution Coevolution two or more species evolve in
response to changes in each other Coevolution two or more species
evolve in response to changes in each other Benefit to both species
Benefit to both species Plants and bees Plants and bees
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- Patterns in Evolution Coevolution can also drive predator-prey
relationships Cheetahs and gazelles
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- Patterns in Evolution Extinctions species are eliminated
Extinctions species are eliminated Background extinctions occur
continously, but at very low rates Background extinctions occur
continously, but at very low rates Mass extinctions rare, more
intense, involve many species Mass extinctions rare, more intense,
involve many species
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- Patterns in Evolution Punctuated equilibrium bursts of
evolutionary activity followed by periods of inactivity Punctuated
equilibrium bursts of evolutionary activity followed by periods of
inactivity Adaptive radiation diversification of multiple species
from one ancestral species Adaptive radiation diversification of
multiple species from one ancestral species Mammals Mammals