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Descent with Modification
How are these pictures
examples of Evolution?
Biological Evolution
Change in the genetic makeup of a
population or species over time.
We can influence evolution over
time through selective breeding.
A group of individuals belonging to the
A group of populations
whose individuals
have the potential to
interbreed and
produce fertile
Gene Pool
•The total
aggregate of
genes in a
population at
any one time.
Population Genetics
•The study of genetic changes in
How are these pictures examples of
Biological Evolution?
•Change that occurs within a
species over time; a change in the
gene pool of a population over a
succession of generations.
Mechanisms of Microevolution
1. Genetic Drift: changes in a gene
pool of a small population due to
chance (usually reducing genetic
How does the picture in your
lab book explain genetic
A. Bottleneck Effect
• Type of genetic drift resulting from a
reduction in population (natural
disaster) such that the surviving
population is no longer genetically
representative of the original
B. Founder Effect:
•A cause of genetic drift
attributable to colonization by a
limited number of individuals
from a parent population.
2. Gene Flow
Genetic exchange due to the migration
of fertile individuals or gametes
between populations (reduces
differences between populations).
3. Mutations
•Random changes in the DNA
The Attack of the Killer Bee!
4. Non Random Mating
Inbreeding and asortive mating
(both shift frequencies of different
5. Natural Selection
Differential success in
reproduction; adapts a population
to its environment.
Population Variation
•Changes within a population.
Polymorphism: coexistence of 2 or
more distinct forms of individuals
within the same population.
Geographical variation:
differences in genetic structure
between populations
Sexual Selection
Selection towards secondary sex
characteristics that leads to sexual
dimorphism (separate
•Change that occurs among
species over time as new species
evolve and old species become
extinct. The origin of new
taxonomic groups.
–For example, macroevolution is
evolution on the “grand scale”
resulting in the origin of higher
–Speciation: the origin of a new
Convergent Evolution
Unrelated organisms inhabiting
similar environments will evolve
in similar ways resulting in
similar morphology.
Ex. Hummingbirds and sunbirds
Divergent Evolution
•Two or more populations or
species with common ancestry
become more dissimilar in
response to evolution in different
adaptive radiation
artificial selection