Download Population Genetics & Evolution

Population Genetics &
Evolution
Population Genetics &
Evolution
• Individuals do not evolve but
populations do
Genetic Equilibrium
• Occurs when the frequency of alleles
remains the same over generations
within a population
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Genetic Equilibrium
• Gene pool - All of the alleles of a
population’s genes
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Genetic Equilibrium
• Allele Frequency - percentage of a
specific allele in the
gene pool
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Genetic Equilibrium
• A population that is in genetic
equilibrium is NOT evolving
Genetic Equilibrium
• Anything that affects the genes in a
gene pool can change allelic
frequencies, which will disrupt a
population’s genetic equilibrium and
result in the process of evolution
Mechanisms that disrupt a
population’s genetic
equilibrium
• Mutations: introduce new alleles into the
gene pool & change allelic
frequencies
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Mechanisms that disrupt a
population’s genetic
equilibrium
• Genetic drift - alteration of allelic
frequencies by chance
events
• Occurs mainly in small populations that
interbreed with each other
Example of Genetic Drift
• Allele for extra fingers & toes is 1 out of
14 in Amish people but 1 out of 1000 for
the rest of the U.S. population
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Mechanisms that disrupt a
population’s genetic
equilibrium
• Gene flow - transport of genes by
migrating individuals
Genes are lost from the gene pool when
an individual leaves a population; genes
are added when an individual enters a
population
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Mechanisms that disrupt a
population’s genetic
equilibrium
*The 3 mechanisms previously described
primarily affect evolution of small,
isolated gene pools (like those on
islands) but their effect is often
insignificant in larger, less isolated gene
pools*
Mechanisms that disrupt a
population’s genetic
equilibrium
• Natural selection - the most significant
factor that causes changes in
established gene pools, whether they
are large or small
• There are 3 types of natural selection:
stabilizing, directional, & disruptive
Stabilizing Natural Selection
• Favors the average individuals in a
population
• Reduces variation in a population
Directional Natural Selection
• Favors individuals with one of the
extreme variations of a trait
• Can result in rapid evolutionary change
within a population
Disruptive Natural Selection
• Favors individuals with either extreme of
a traits variation
• Can lead to evolution of 2 distinct
species
The End