Transcript Chapter 11 Evolution of Populations

The
Evolutio
n of
Populati
ons
Chapter 11
Why is it important to study the genes?
In a population the
combination of all of
the genes for a given
species is called the
gene pool.
As the number of
species diminishes the
gene pool gets smaller.
A small gene pool is
one of the causes of
extinction.
The relative frequency
of a gene shifts as the
population grows and
shrinks.
Mutations that are
expressed will cause a
shift of the relative
frequency and possible
speciation over time.
A
gene
pool?
The genes are confined to a given
population
If no change occurs they are in
genetic equilibrium
What happens as the number of
individuals changes?
Natural selection
on single-gene traits
can lead to changes
in allele frequencies
and thus to evolution.
Remember the
change in the gene
must be expressed
phenotypically or no
change will occur
Three
Patterns of Natural Selection
Remember it acts on phenotype!
Directional Selection
Disruptive Selection
Stabilizing Selection
Directional
Extreme phenotype once
rare becomes common
Disruptive
Both extremes are favored,
intermediate fades out
Stabilizing
Intermediate
phenotype is favored
Genetic Variation can come from
Mutation- natural or induced through
toxins or radiation
Recombination- remember crossing- over
in Meiosis
HybridizationSelective breeding
bioengineering
Genetic Drift
A change in the allele frequency due to chance
Seen more
frequently in
smaller
populations
Causes a loss of
genetic diversity
within a population
Bottleneck effect,
reduction of
population
Founders effect,
new population
The Problem with Genetic Drift
is that recessive lethal mutations
can occur at a higher frequency.
What factors must exist for
speciation to occur?
Reproductively isolatedcan be by behavior
Geographically isolated
populations divided by mountains
or oceans
Temporal isolationreproduce at different times
What patterns
have we seen in
Evolution?
Convergent Evolution
Unrelated organisms that look similar
Mimicrydifferent
species mimic
their toxic
Darwin’s Finches
Divergent Evolution
Adaptive Radiation is synonymous with Divergent evolution
Mass
extinction
25-70%
of species
wiped out
5
4
3
Generally
followed
by a
period of
adaptive
radiation
2
1
When a mass extinction occurs
the period following it is followed by
speciation & adaptive radiation
There are many unoccupied niches!