Transcript Population Genetics and Natural Selection

BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Darwin
• 1835 _____________visited the Galapagos
Islands and became convinced various
populations evolved from ancestral form.
• 1838 After reading an essay by
__________________, he theorized some
individuals would have a competitive
advantage conferred by favorable
characteristics.
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Darwin’s Theory of Natural Selection
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– Some are heritable.
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
• Augustinian Monk
– Studied garden pea (Pisum sativum).
– Discovered characteristics pass from parent to
offspring in form of discrete packets called genes.
• Exist in alternate forms - alleles.
• Some prevent expression of others.
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Big Picture…
• Phenotypic variation among individuals in a
population results from the combined effects
of …
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Big Picture…
• The Hardy-Weinberg equilibrium model helps
identify …
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Big Picture…
• ________________ is differential survival and
reproduction among phenotypes.
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Big Picture…
• The extent to which phenotypic variation is
due to genetic variation determines ….
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Big Picture…
• Random processes, such as genetic drift, can…
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Variation Within Populations
• Variation in Plant Populations
– Many plant species differ dramatically in form
from one elevation to another.
• Clausen et al. found evidence of adaptation by
ecotypes to local environmental conditions in Potentilla
glandulosa.
–
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Variation Within Populations
• Variation in Plant Populations
– Phenotypic differences (growth and flower
production) within clones grown at the 3
elevations are the result of environmental
differences
•
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Variation in Animal Populations
• Genetic Variation in Alpine Fish
– Movement of cold adapted aquatic species into
the headwaters of glacial valleys that lace the Alps
created clusters of geographically isolated
populations.
• Douglas and Brunner used microsatellite DNA to
conclude Coregonus populations are …
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Hardy Weinberg
• Hardy Weinberg principle states that in a
population mating at random in the absence
of evolutionary forces, allele frequencies will
remain constant.
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Calculating Gene Frequencies
• SS (81%)
SA (18%) AA (1%)
– Frequency of S allele ?
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=
–
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Conditions Necessary for Hardy
Weinberg
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…Between All Genotypes
– Likely, at least one of these will not be met and
allele frequencies will change.
• Potential for evolutionary change in natural populations
is very great.
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Natural Selection
• Some individuals in a population, because of
their phenotypic characteristics, will have
higher survival and produce more offspring.
– ________________ is the measure of an
individual’s contribution of offspring, or genes, to
future generations.
– Natural selection can…
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Stabilizing Selection
• __________________ acts to impede changes
in a population by acting against extreme
phenotypes and favoring average phenotypes.
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Directional Selection
• ____________________ leads to changes in
phenotypes by favoring an extreme
phenotype over other phenotypes in the
population.
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Disruptive Selection
• ________________ creates bimodal distributions
by favoring two or more extreme phenotypes
over the average phenotype in a population.
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Evolution by Natural Selection
• Natural selection, which changes genotypic
and phenotypic frequencies in populations,
can result in adaptation to the environment.
– Depends on ________________ of trait.
h2 = VG / VP
• VG : Genetic variance
• VP: Phenotypic variance
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Adaptive Change in Colonizing Lizards
• Losos et al.
– Genus Anolis
• Great diversity includes large amount of variation in
size and body proportions.
– Length of hind limbs appears to reflect …
» Diameter of perching surfaces.
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Rapid Adaptation by Soapberry Bugs
• Carroll and Boyd
– Soapberry Bug (Jadera haematoloma) feeds on
seeds from family Sapindaceae.
• Slender beaks to pierce fruit walls.
– Distance from outside fruit wall to seeds varies widely - …
» Found close relationship between …
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Change Due To Chance
• Working in teams complete the
simulation on Population Genetics…
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Change Due To Chance
• Random processes such as _____________ can
change gene frequencies in populations,
especially in small populations.
• Major concern of ____________________ is
reducing habitat availability to the point where
genetic drift will reduce genetic diversity within
natural populations.
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Evidence of Genetic Drift in Chihuahua
Spruce
• Picea chihuahuana now restricted to peaks of
Sierra Madre Occidental in N. Mexico.
– Ledig et al. examined populations to determine if
the species has lost genetic diversity as a
consequence of reduced population size.
• Found significant …
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Genetic Variation In Island Populations
• In general, genetic variation is _________ in
isolated and generally smaller, island
populations.
– Reduced genetic variation indicates a lower
potential for a population to evolve.
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Genetic Diversity and Butterfly
Extinctions
• Frankham and Ralls point out ___________
may be a contributor to higher extinction rates
in small populations.
– Reduced fecundity, depressed juvenile survival,
shortened life-span.
• Saccheri et al. conducted genetic studies on
populations of Glanville fritillary butterflies
(Melitacea cinxia).
– Populations with highest levels of inbreeding had…
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Evolution and Agriculture
• “_____________________” is used to
describe selective breeding of domesticated
organisms to produce or maintain desirable
traits.
• “_____________________” is the
introduction or deletion of genes in
domesticated organisms.
– These organisms are termed “genetically modified
organisms” or GMOs.
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
Unintended Evolutionary
Consequences
• The use of chemicals in agriculture can have
evolutionary consequences
– Plant and animal pests may evolve resistance to
the chemicals used to control them
• Resistance among pests have been shown to be quick
and widespread
– Vila-Aiub et al. showed how Johnsongrass quickly evolved
resistance to herbicides in Argentina
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BIOL 3240 Plant and Animal Ecology –
Population Genetics and Natural Selection
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