Download Mechanisms of Evolutionary Change

Mechanisms of Evolutionary Change
(other than natural selection)
SC.912.L.15.14
What can change a gene pool
other than natural selection?
1.
2.
3.
Genetic Drift
Gene Flow
Mutations
Genetic drift
 Genetic Drift: A change in the gene pool of a
population due to chance
 the smaller the population is, the more impact genetic drift has
on that population
Only the alleles of organisms that successfully reproduce in one generation appear in the gene pool of
the next generation.
In this population of ten plants, the frequency of white-flower alleles was reduced to zero due to
genetic drift
Genetic
Drift
Bottleneck Effect
 Disasters such as earthquakes, floods, droughts, and fires
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may drastically reduce the size of a population
Reducing the size of the population also reduces the size
of its gene pool
By chance, certain alleles may then be represented more
frequently than others among the survivors
Some alleles may be eliminated altogether
Decreases genetic variation in a population
Marbles falling through
the narrow neck of a
bottle serve as an analogy
for the bottleneck effect.
Compared to the original
population (in the bottle)
the new population has
less variation.
The loss of variation due
to a bottleneck effect
could reduce the ability of
a population to adapt to
environmental change
The Cheetah
 May have suffered one or more
bottleneck events
 Sharp decrease in the cheetah
population occurred during the
last ice age about 10,000 years ago
 Farmers hunted the animals to
near extinction
 The cheetah populations may not
be able to resist disease or adapt to
other environmental challenges to
their survival
Bottleneck
Effect
What else can effect the gene
pool?
Gene Flow
Mutation
Gene flow: The exchange of genes with
another population
1.
2.
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Occurs when fertile individuals or their gametes (sex cells)
migrate between populations
Can increase or decrease genetic variation within a
population
Tends to reduce genetic differences between populations
Mutation
 Mutation: a change to the genetic material
 Natural selection or genetic drift (or both) can influence
whether the frequency of a new mutation increases in a
population
 Example- albino deer
 Plays a key role in evolution as the original source of the
genetic variation that is the raw material for natural
selection
 Especially important as a source of variation in asexually
reproducing organisms that clone themselves rapidly,
such as bacteria
Make a Venn Diagram
 Compare and contrast Genetic Drift, Gene Flow, and
Mutations
Venn
Diagram