Download Evolution as Genetic Change and Speciation

Evolution as Genetic Change
and Speciation
A Population’s Gene Pool
A gene pool is all the
alleles available in all
of the individuals in a
population
How do we know a population is
evolving?
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When there are changes in the frequency of
alleles in the gene pool (aka Microevolution)
How do the allele frequencies change?
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Natural Selection (directional, stabilizing,
disruptive, or sexual selection)
Random Change (mutations, genetic drift, or
gene flow)
Migration
Genetic Drift
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The random change in the gene
pool of a population
All populations are subject to
genetic drift, but small
populations are impacted more
Bottleneck Effect: Occurs when a
natural disaster greatly reduces
the size of the population and the
gene pool (population loses
variation)
Founder Effect: Occurs when a
few individuals from a population
colonize an isolated island or new
habitat (population loses genetic
variation)
Gene Flow
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Gene flow occurs when genes are
exchanged with another population (ex:
migration)
Gene flow can reduce genetic differences
between populations, possibly uniting the
gene pool in a single population
Mutations
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The random change in the DNA of an
organism
The frequency of a mutation in the
population will depend on the effects of
natural selection- will it make the
individual more likely to survive and
reproduce?
Hardy-Weinberg Equilibrium
Evolution will NOT occur (allele frequencies
remain constant) if the following
conditions are met:
1. Random mating
2. No emigration or immigration
3. Population must be large
4. No natural selection
5. No mutations
Evolution of a Species
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Biological Species Concept: a species is a
population that will interbreed and produce
fertile offspring
When a population evolves enough genetic
change (either through natural selection,
genetic drift, etc.) that it no longer
interbreeds with the original population, it
is considered a new species
An Example of Speciation
1.
2.
3.
4.
A species contains one
population or several
interbreeding populations
A barrier comes between the
populations
Natural selection occurs
Barrier is removed,
reproductive isolation has
occurred, two species now exist
Other Reproductive Barriers
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Temporal (timing)- different mating seasons
Behavioral- different courtship or mating
behaviors
Habitat- Fish living in streams verses open water
Geographic- populations divided by barriers like
glaciers, valleys, rivers, etc.