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Mechanisms
of Evolution
Mechanisms of Evolution
There are several:
1. Natural Selection
2. Gene Flow
3. Genetic drift
4. Mutations
5. Non-random mating
1. Natural Selection:
• Variation exists within a population
• More offspring are born than can
survive
• Phenotypic differences result in
differential reproductive success
• Individuals that do survive, pass
heritable traits on to offspring
• Over time (many generations) this
could lead to changes in the
population
Natural Selection
2. Gene Flow:
 Is the movement of alleles into or out
of a population (immigration or
emigration).
 Gene flow can introduce new alleles
into a gene pool or can change allele
frequencies.
 Example:
 Plant pollen being blown into a new
area
Gene Flow
3. Genetic Drift
 The change in allele
frequencies as a result of
random chance.
 Affects small populations.
Examples of Genetic Drift
 B) Population Bottleneck:
 Occurs when a population undergoes an
event in which a significant percentage
of a population or species is killed or
otherwise prevented from reproducing.
•The event may eliminate
alleles entirely or also
cause other alleles to be
over-represented in a
gene pool.
EX. Cheetahs
4. Mutations
 Are inheritable changes in the
genotype.
 Provide the variation that can be
acted upon by natural selection.
 Mutations provide the raw
material on which natural
selection can act.
5. Non-Random Mating
 In animals, non-random mating can
change allele frequencies as the
choice of mates is often an
important part of behavior.
 **Dog Breeders**

Mimicry Coral snakes (venomous) and king snakes (nonvenomous) The harmless king snake mimics the poisonous
coral snake, causing would-bepredators to avoid them.
http://3.bp.blogspot.com Monarchs (toxic to predators)
and viceroys (non-toxic) The viceroys mimics the
coloration and pattern of the unpalatable monarch,
also avoiding would-be-predators.
http://fish.mongabay.com Camouflage: A flounder will
be less conspicuous to predators and to would-be prey if
it blends in with its environment.
http://conservationreport.files.wordpress.comCompar
e/contrast mimicry and camouflage. Pick an organism and
explain the benefit of that animal or pl