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Transcript
Other Mechanisms of Evolution
KEY CONCEPT
Natural selection is not the only mechanism through
which populations evolve.
Other Mechanisms of Evolution
Gene flow
• Definition: Movement of
alleles from one
population to another
• How it works: When
animals move from one
population to another &
breed in the new
population; when spores
or seeds of plants or
fungi are spread to new
areas
bald eagle migration
Other Mechanisms of Evolution
Gene flow:
• Lots of gene flow
between populations
Results in
• Lots of gene flow
Results in
between populations
Similar populations
(genetically)
Different populations
(genetically) that could
evolve into different
species
Other Mechanisms of Evolution
Genetic drift
• Definition: Changes in allele frequencies due to chance
alone
• How it works: Small populations are more likely to be
affected by chance; Due to chance some alleles may
increase in frequency while others may decrease & even
become eliminated from the population
Other Mechanisms of Evolution
Genetic drift
• Key Terms
– Bottleneck effect: Genetic
drift that occurs after an
event drastically reduces the
size of a population
– Founder effect: Genetic drift
that occurs after a small
number of individuals
colonize a new area
• Negative effects: Population loses genetic variation, so
population is less likely to have some individuals that will be
able to adapt to a changing environment; harmful alleles
may become more common due to chance alone
Other Mechanisms of Evolution
Sexual selection
• Definition: Process in which
certain traits increase mating
success & therefore become
more common in the population.
• How it works: Females
preferentially mate with males
that display certain traits, so
those traits get passed onto
offspring & can become more
exaggerated each generation
Other Mechanisms of Evolution
Sexual selection
• Types
– Intrasexual: Competition/fighting
among males for females
– Intersexual: Males display certain
traits to attract females