Examples of Evolution
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Examples of Evolution
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Allele Frequencies
There are dominant and recessive alleles.
Hardy and Weinberg (scientists) determined that
dominant alleles do NOT automatically replace recessive
alleles.
Alleles in a population only change if selection acts upon
them
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http://campus.murraystate.edu/academic/faculty/terry.derting/bio116/hardy_weinberg.jpg
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HARDY-WEINBERGPRINCIPLE:
The frequencies of alleles in a population do not change
unless evolutionary forces act on the population.
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Hardy-Weinberg
• Holds true for:
• large populations in which members do not mate with relatives AND
• as long as evolutionary forces are not acting on the population
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5 Evolutionary Forces
1.Mutations
2.Gene Flow
3.Nonrandom mating
4.Genetic drift
5.Natural Selection
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#1 Mutations
• Mutation rates are slow in nature
• Not all result in phenotype changes (remember the codon wheel)
• Mutation IS the source of variation though & makes evolution possible
• http://www.youtube.com/watch?v=MkmtodFQbQM
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#2 Gene Flow• The movement of individuals to or
from a population (MIGRATION) creates gene flow.
• Immigrants = arriving individuals
• Emigrants = departing individuals
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#3 Nonrandom Mating
• In-breeding alters Hardy-Weinberg
• Also occurs when organisms choose their mates
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#4 Genetic drift
• Small populations that are isolated from one another can differ greatly because of genetic drift
• Fires - landslides - etc.
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# 5 Natural Selection
• The frequency of an allele will increase or decrease depending on the allele’s effects on survival and reproduction
• N.S. is one of the most powerful agents of genetic change.
http://evolution.berkeley.edu/evolibrary/article/evo_39
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Natural Selection affects the Distribution of Phenotypes in 4 Ways!
1 – Stabilizing Selection 2 – Directional Selection3 – Disruptive Selection4 - Sexual Selection
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1- Stabilizing Selection
• Individuals with the average form of a trait have the highest fitness.
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2 – Directional Selection
• Individuals at one end of the curve have higher fitness and are favored more than individuals in the middle or other end.
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3 – Disruptive Selection
• Individuals with either extreme variation of a trait have greater fitness than individuals with the average form of the trait.
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4 – Sexual Selection
• The preferred choice of a mate based on a specific trait.
Peacocks
-- females choose
males based on
certain traits
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V. I .S .T.
• V = Variation: All life forms vary genetically within a population. It is this genetic variation upon which selection works.
• I = Inheritance: Genetic traits are inherited from parents and passed on to offspring.
• S = Selection: Organisms with traits that are favorable to their survival get to live and pass on their genes to the next generation.
• T = Time: Evolution takes time. It can happen in a few generations, but major change, such as speciation, often take very long periods of time.