on truth in biology : "the only thing always true in biology is that there are always...
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On truth in Biology :
"the only thing always true in biology is that there are
always exceptions..."
Dr. Rita CalvoCornell University
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microevolutmicroevoluti
microevolutio
microevolution
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Microevolution:Microevolution: generationgeneration--toto- -
generationgeneration changeschanges in in alleleallele or or genotypic genotypic frequencies.frequencies.*genetic *genetic changes in a changes in a
gene poolgene pool**look, it’s Jennifer!
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Microevolution:Microevolution: alleleallele or or
genotypic genotypic frequency changes…frequency changes…HOW????HOW????
1) Mutations… of germ cells
(those that produce gametes!!!)
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Microevolution:Microevolution: alleleallele or or
genotypic genotypic frequency changes…frequency changes…HOW????HOW????
Point mutationstranslocations
Gene duplication ex. Gene for smell
Jumping genes
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Microevolution:Microevolution: alleleallele or or
genotypic genotypic frequency changes…frequency changes…HOW????HOW????2) Sexual
recombination
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BIGBIG Microevolution Microevolution
causes:causes:
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BIG BIG Microevolution Microevolution
causes:causes:1) Genetic drift -
randomrandom, , evolutionary evolutionary changeschanges in small populations - due to due to chancechance… not due to natural selection!!!
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The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better” individuals.
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If the gene for green coloration drifts out of the population, the gene is gone for good—unless, of course, a mutation or gene flow reintroduces the green gene.
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the most important effects of genetic drift: it reduces the amount of genetic variation in a population. And with less genetic variation, there is less for natural selection to work with. If the green gene drifts out of the population, and the population ends up in a situation where it would be advantageous to be green, the population is out of luck. Selection cannot increase the frequency of the green gene, because it’s not there for selection to act on. Selection can only act on what variation is already in a population; it cannot create variation.
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BIG BIG Microevolution Microevolution
causes:causes:1) Genetic drift -(the smaller the sample,
the quicker & more drastic the change effect! greater the chance of deviations from the expected
probability.)
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BIG BIG Microevolution Microevolution
causes:causes:Genetic drift -
Population must be Population must be largelarge in order to in order to rulerule outout changes changes
due to chance as an due to chance as an agent of evolutionagent of evolution
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BIG BIG Microevolution Microevolution
causes:causes:Genetic drift -
The larger the population, the more closely
related the genes will resemble the
previous population.
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1) BOTTLENECK EFFECT1) BOTTLENECK EFFECT
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1) BOTTLENECK EFFECT1) BOTTLENECK EFFECT
Certain alleles become under-represented
Where did the white ones go?
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1) BOTTLENECK EFFECT1) BOTTLENECK EFFECT
Some alleles are eliminated altogether
Where did the orangeorange ones go?
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1) BOTTLENECK EFFECT1) BOTTLENECK EFFECT
Some alleles are overrepresented
Are there proportionally more blue ones now?
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BOTTLENECK EFFECTBOTTLENECK EFFECT
• Reduction of population size may reduce gene pool for
evolution to work with•ex.CHEETAHSex.CHEETAHS•Some genes Some genes are not are not
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FOUNDERS EFFECTFOUNDERS EFFECT
New colony
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FOUNDERS EFFECTFOUNDERS EFFECT
New colony
Disproportionate
New colony
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FOUNDERS FOUNDERS EFFECTEFFECT
•Genetic drift in a new colony that separates from a parent population.
•Reduces genetic variability
•ex. Old-Order Menonite ~ hearing disorder
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BIG BIG Microevolution Microevolution
causes:causes: 2) Gene flow (also called
migration)
any movement of genes from one population to another.
Gene flow includes many different kinds of events:
pollen being blown to a new destination or
people moving to new cities or countries.
If genes are carried to a population where those genes previously did not exist, gene flow can be
a very important source of genetic variation.
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BIG BIG Microevolution Microevolution
causes:causes: 2) Gene flow
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BIG BIG Microevolution Microevolution
causes:causes: Gene flow -
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BIG Microevolution BIG Microevolution causes:causes: Nonrandom mating - select a mate based upon phenotype (and what they smell like… hmmmm)
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BIG Microevolution BIG Microevolution causes:causes: Nonrandom mating - select a mate based upon phenotype (and what they smell like… hmmmm)
http://www.pbs.org/wgbh/evolution/library/01/6/l_016_08.html
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BIG BIG Microevolution Microevolution causes:causes: 4) Natural Selection -over generations, the proportion of favorable alleles survive.
All individuals are not equal in their ability to survive &
reproduce
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Different ways this happens:
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characteristics vary: Within the
Population
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Genetic Genetic Variation =Variation =
Within the Population -
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phenotypic phenotypic polymorphismpolymorphism
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Garter Snakes Gaillardia
phenotypic phenotypic polymorphismpolymorphism
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genotypic genotypic polymorphismpolymorphism
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Genetic Genetic VariationVariation
Between Populations - Clinal
Along a geographic Along a geographic axisaxis
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Selection of genetic variation
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N. Selection of genetic variation Here is the base-line:
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Selection of genetic variation stabalizing selection:
ex. Birth weight in babies
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•Elimination of
extreme phenotypes. Favors
intermediate This reduces variation
Selection of genetic Selection of genetic variationvariation
Stabalizing selection:
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Selection of genetic Selection of genetic variationvariation
Directional Selection:
ex. Galapagos Island finch beak size
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Elimination of
intermediate phenotypes.
Favors the rare This reduces variation
Selection of genetic Selection of genetic variationvariation
Directional Selection:
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Selection of genetic Selection of genetic variationvariation Diversifying Selection:
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Elimination of intermediate phenotypes.
Favors the extremes.
This reduces variation
Selection of genetic Selection of genetic variationvariation Diversifying Selection:
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Question• Does evolution result in perfect
organisms?
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Misconception: “Natural selection gives
organisms what they ‘need.’ ”
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Summary•Know the difference between a species and a population.
•Know that the unit of evolution is the population and not the individual.
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Summary•Know the H-W equations and how to use them in calculations.
•Know the H-W assumptions and what happens if each is violated.
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Summary•Identify various means to introduce genetic variation into populations.
•Know the various types of natural selection.