Microevolution
Outline
Main Goal: To Understand:
• What is microevolution?
• What are the results of natural selection on phenotype?
• How can you tell if a population is going through
microevolution?
SJCHS
March 2011
Evolution
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Microevolution: Change in a population’s (group of same species in
same area) gene pool from generation to generation
• Gene Pool: Frequency of different alleles (traits) in a
population
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Mechanisms of Microevolution
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Natural Selection: Individuals whose inherited traits are best suited to
local environment are more likely than less “fit” individuals to
survive and reproduce
Natural Selection
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Mechanisms of Microevolution
•
Mutations: Change in DNA that is the ONLY process that can result
in a new trait appearing in organism
• Random process
• Rare process
• Must mutate gametes (sperm or egg cells) in order for the
trait to be passed to offspring
Outcomes to population phenotype (traits):
Directional Selection: Extreme traits
Disruptive Selection: Balance between 2 or more traits
Stabilizing selection: Traits within a narrow range
• Most common
Mechanisms of Microevolution
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Genetic Drift: Random changes in gene pool of a small population due
to chance
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Mechanisms of Microevolution
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Bottleneck event: Disaster causes death of large numbers in population
which results to a change in the gene pool
Mechanisms of Microevolution
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Founder event: Small part of population moves to isolated habitat
• Gene pool will be different than larger population
Mechanisms of Microevolution
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Gene Flow: Gene pool changes as organisms move in and out of
population
Hardy Weinberg
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Hardy Weinberg Theorem: Mathematical model used to determine if a
population’s gene pool changing (is microevolution occurring?)
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