Download MECHANISMS OF EVOLUTION

MECHANISMS
OF EVOLUTION
POPULATIONS, NOT
INDIVIDUALS, EVOLVE
An organism cannot change
its phenotype. A phenotype
can become more
predominant in a population,
though.
Gene Pool
All the alleles of the
population’s genes.
ALLELIC FREQUENCY
The percentage of any
specific allele in the gene
pool.
GENETIC EQUILIBRIUM
A population in which
the allele frequencies
remain the same over
many generations.
CHANGES IN GENETIC
EQUILIBRIUM
A population in genetic
equilibrium is not evolving.
When equilibrium of the gene
pool is disrupted, evolution
occurs.
Changes in equilibrium
may be the result of
mutations.
Gene Flow
Organisms moving in
(immigration) or out
(emigration) of a population
creates changes in the
allelic frequencies of the
gene pool.
Hardy-Weinberg Principle
• In order for genetic equilibrium
to remain, these conditions
must be met:
–No mutations
–No immigration or emigration
–Random mating
GENETIC DRIFT
The alteration of allelic
frequencies by chance
events.
Can greatly affect small
populations.
NATURAL SELECTION ACTS ON
VARIATIONS
THE EVOLUTION OF
SPECIES
SPECIATION
• Occurs when members of
similar populations no
longer interbreed to produce
fertile offspring within their
natural environment.
PHYSICAL BARRIERS CAN
PREVENT INTERBREEDING
-Geographic isolation
-Reproductive isolation
CHANGE IN CHROMOSOME
NUMBER
SPECIATION CAN OCCUR
QUICKLY OR SLOWLY
GRADUALISM
• The idea that species
originate through a
gradual change of
adaptations. Example:
horses in fossil record.
PUNCTUATED EQUILIBRIUM
• The idea that speciation
occurs in rapid bursts with long
periods of genetic equilibrium
between.
• Caused by abrupt temperature
changes or introduction of a
competitive species.
PATTERNS OF EVOLUTION
ADAPTIVE RADIATION
• Many species evolve from a
single species.
• Example – Darwin’s finches
and Hawaiian Island
honeycreepers.
DIVERGENT EVOLUTION
• Two or more species
with the same common
ancestor become
different species due to
isolation.
CONVERGENT EVOLUTION
• Two species with
different ancestors
evolve similar traits due
to selective pressures in
the environment.