Transcript natural selection

MECHANISMS FOR EVOLUTION
• DO POPULATIONS OR INDIVIDUALS EVOLVE?
• WHAT IS A GENE POOL
• HOW CAN THE GENE POOL CHANGE?
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MUTATION
GENETIC DRIFT
GENE FLOW
NON-RANDOM MATING
NATURAL SELECTION
• WOULD THESE THINGS EFFECT A LARGE POPULATION OR A
SMALL POPULATION MORE?
Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.
CAUSES OF MICROEVOLUTION
 MUTATIONS – provide new alleles in a population
and provide the variation for evolution to occur,
should the mutation lead to some adaptive advantage.
 Mutation alone does not cause evolution, but provide a
selective advantage that due to natural selection can
lead to a shift in allele frequency.
CAUSES OF MICROEVOLUTION
• GENETIC DRIFT – in small populations the
frequencies of alleles can be drastically affected by
chance events
– BOTTLENECK EFFECT – if populations are driven to the
point of extinction the remaining individuals do not
carry a true representation of the original gene pool.
– FOUNDER EFFECT – when a small number of
individuals colonize a new area they only carry with
them a small representation of the total number of the
alleles from the gene pool.
 GENE FLOW – genetic exchange between
populations due to migration
 NONRANDON MATING
 Breed with other members of the
“neighborhood” promotes inbreeding
 Assortative mating – mate with others like
themselves . This is the premise behind artificial
selection.
CAUSES OF MICROEVOLUTION
 NATURAL SELECTION – any environmental factor
that leads to a particular allele having some adaptive
advantage.
 There are three ways that natural selection can affect
the frequency of traits:
 Stabilizing selection
 Directional selection
 Disruptive selection
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Sexual Selection
 Sexual reproduction has evolved independently
numerous times throughout history.
 External Internal
 Motility and Numbers (sperm)
 Pheromones/sexual behaviors/attractants
 Sexual Dimorphism – differences between males and
females in looks and behaviors.
Benefits of Sex
 It costs a lot so why do it????
 Sex creates diversity