Transcript Chapter 16

Chapter 16
Population Genetics and Speciation
Objectives
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CLE 3210.5.3 Explain how genetic
variation in a population and changing
environmental conditions are associated
with adaptation and the emergence of
new species.
Darwin’s
Finches
http://people.rit.edu/rhrsbi/GalapagosPages/Pictures/LandBirds/FinchType
http://www.biology-online.org/images/darwin_finches.jpg
Five conditions under which
evolution may take place
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Genetic mutations
Gene flow
Genetic drift
Nonrandom mating
Natural selection.
Mutation
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Mutations are changes in the DNA.
Gene Flow
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Emigration and immigration cause
gene flow between populations and
can thus affect gene frequencies.
Genetic Drift
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Genetic drift is a change in allele
frequencies due to random events.
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Genetic drift operates most strongly
in small populations.
Nonrandom Mating
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Mating is nonrandom whenever
individuals may choose partners.
Sexual selection occurs when certain traits
increase an individual’s success at mating.
 Sexual selection explains the development
of traits that improve reproductive success
but that may harm the individual.
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Natural Selection
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Three general patterns
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Stabilizing Selection
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Disruptive Selection
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favors the formation of average traits.
favors extreme traits rather than average traits.
Directional Selection
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favors the formation of more-extreme traits.
The Concept of Species
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Biological species concept
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a species is a population of organisms
that can successfully interbreed but
cannot breed with other groups
Isolation and Speciation
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Geographic Isolation
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Allopatric Speciation
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Speciation due to separation of subgroups of a population
Reproductive Isolation
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Results from the separation of population subgroups by
geographic barriers.
Results from the separation of population subgroups by
barriers to successful breeding.
Sympatric Speciation
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Reproductive isolation within the same geographic area
Allopatry vs Sympatry
http://deltabiology.com/wp-content/uploads/2012/02/Sympatry.jpg
http://scienceblogs.com/evolvingthoughts/allopatry.jpg
Reproductive isolation:
Monkeyflower
http://faculty.washington.edu/toby/images/mim29%20Nature.jpg
Reproductive isolation
http://evolution.berkeley.edu/evolibrary/images/evo/drosophila_scene7.g
Rates of Speciation
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Gradualism
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species undergo small changes at a constant rate.
Punctuated equilibrium
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new species arise abruptly, differ greatly from their
ancestors, and then change little over long periods.
Variation of Traits Within a
Population
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Variations in genotype arise by mutation,
recombination, and the random pairing of
gametes.
The Gene Pool
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The total genetic information available in a
population is called the gene pool.
Allele frequency is determined by dividing the
total number of a certain allele by the total
number of alleles of all types in the population
Predicting Phenotype
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Phenotype frequency is equal to the number of
individuals with a particular phenotype divided by
the total number of individuals in the population.
The Hardy-Weinberg Genetic
Equilibrium
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Allele frequencies in the gene pool do not
change unless acted upon by certain forces.
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Hardy-Weinberg genetic equilibrium is a
theoretical model of a population in which no
evolution occurs and the gene pool of the
population is stable.
Phenotype Frequency
Calculating using the Hardy
Weinberg equation
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Dominant allele frequency = p
Recessive allele frequency = q
p+q=1
p2 +2pq+ q2 = 1