ch 16 evolution of populations
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Ch 16 Evolution of populations. Crash Course: Population Genetics. https://www.youtube.com/watch?v=WhFKPaRnTdQ. 16-1 Genetic equilibrium. Population genetics : study of evolution from a genetic point of view Basically how populations of a species evolve But what is a population? - PowerPoint PPT PresentationTRANSCRIPT
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CH 16EVOLUTION OF POPULATIONS
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Crash Course: Population Genetics https://www.youtube.com/watch?v=WhF
KPaRnTdQ
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16-1 Genetic equilibrium Population genetics: study of
evolution from a genetic point of view Basically how populations of a species
evolve But what is a population? Group of members of the same species
living in the same area
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Sources of genetic variation Three main sources1. Mutations: any change in sequence of
DNA Replication mistakes Radiation/environmental causes
2. recombination: reshuffling of genes3. Random pairing of gametes
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Bell curve Many traits in nature show trends like
this
Phenotype continuum
# of
indi
vidu
als w
ith th
at tr
ait
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Number of phenotypes produced depends on how many genes control that trait
Single gene traits- have two alleles Two distinct phenotypes
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Polygenic traits- controlled by two or more genes
Results in multiple phenotypes
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Gene pool- all genes, including all different alleles, that are present in a population
frequency (of an allele)- number of times alleles occur in a gene pool Percentage
Genetic definition of evolution? Change in relative frequency of alleles in
a population over time
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Phenotype frequency How often a specific phenotype is
observed in a population Can be written mathematically
Frequency = # indiv. w/a particular phenotype
total # of indiv. in population
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Hardy-Weinberg equilibrium When evolution is not occurring
Allele frequencies remain the same In order for evolution to not occur,
certain conditions must be met.
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Evolution Versus Genetic Equilibrium
Hardy-Weinberg principle = Genetic Equilibrium• Random Mating – Equal opportunity to produce
offspring• Large Population – Genetic Drift does not effect
Allele Frequency• No Movement into or out of Population – The
gene pool must be kept together (no new alleles)• No Mutations – Mutations cause new forms of
alleles changing the frequency• No Natural Selection – All genotypes must have
equal probability of surviving.
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Hardy-Weinberg equilibriumAllele frequency equation p + q = 1 p = frequency of dominant allele q = frequency of recessive alleleTogether, they make 100% of alleles for a gene in that population If p = 34%, what is q? If q = 19%, what is p?
0.660.81
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Hardy-Weinberg equilibrium Genotypic frequency equation
p2 + 2pq + q2 = 1 p2 = homozygous dominant frequency 2pq = heterozygous frequency q2 = homozygous recessive frequency If p = .46, what is p2? If p = .12, what is q2? If q =.31, what is 2pq?
0.21160.7744 = 77%0.4278
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16-2 Disruption of genetic equilibrium
Mutation Occur at a relatively constant rate over
time Can be sped up when exposed to mutagens
Gene flow: process of genes moving from one population to another
Immigration: moving into a population Emigration: moving out of a population
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Genetic Drift Alleles can become rare by chance Over time a series of chance
occurrences can cause an alleles to become common in a population
Effects of genetic drift are more dramatic with small population size
Founder effect: change in allele frequencies as a result of migration of a small subgroup of a population
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Sample of Original Population
Founding Population A
Founding Population B
Descendants
Genetic DriftSection 16-2
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Sample of Original Population
Founding Population A
Founding Population B
Descendants
Genetic DriftSection 16-2
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Sample of Original Population
Founding Population A
Founding Population B
Descendants
Genetic DriftSection 16-2
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Nonrandom mating Sexual selection: tendency of
individuals to choose a mate with certain traits.
Common in birds Peacock display Tropical birds of paradise - Papua New G
uinea The amazing Lyrebird - Australia
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Natural selection Natural selection on a single gene traits
can lead to changes in allele frequencies Natural selection on polygenic traits
3 possible effects1. Directional selection2. Stabilizing selection3. Disruptive selectionhttps://www.youtube.com/watch?v=vCHdT9MWIaA
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Directional selection When individuals at one end of curve
have higher fitness than individuals in the middle or the other end
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Stabilizing selection When individuals near the middle have
higher fitness than the individuals at either end
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Disruptive selection When individuals at upper and lower
ends have higher fitness than individuals near the middle
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16-3 Formation of Species As new species evolve, populations
become reproductively isolated from each other
Reproductive isolation: when two members of populations cannot interbreed and produce fertile offspring
Separate gene pools
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Isolation Mechanisms
Geographic Isolation:- separation of animals in a
specific region- formation of river, canyon,
mountain
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Isolation Mechanisms
Behavioral Isolation:- differences in courtship or reproductive behaviors-meadowlark songsTemporal isolation:
-two or more species reproduce at different times
-orchids
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Formation of species Allopatric
speciation: when species arise from geographic isolation Different places
https://www.youtube.com/watch?v=cSgulsydsQU
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Reproductive isolation Prezygotic isolation:
premating isolation Species may live
in different places Reproduce at different times Have different mating
behaviors Postzygotic isolation:
postmating isolation Hybrids may be weak Hybrids may be sterile
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Sympatric speciation
Sympatric speciation: when two subpopulations become isolated while living in the same area
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Rates of speciation Gradualism:
speciation at gradual and regular rate
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Punctuated equilibrium: periods of sudden, rapid change followed by periods of littelchange