15-2 Mechanisms of Evolution
Can individuals Evolve?
No. Individuals cannot
change once their DNA
is set. A population can
change from generation
to generations.
What is a population?
All the members of a certain species that live in
a certain area at a certain time.
Evolution occurs as a population’s
genes and their frequencies
change over time.
What is a gene pool?
All of the genes available for a
population to draw from.
What is allelic frequency?
The abundance of a
specific gene in a
population’s gene
pool (also the
probability of a
certain gene
becoming expressed
in an offspring).
What is genetic equilibrium?
A population in which the
frequency of genes remains
constant over generations.
Is a population that is in genetic
equilibrium evolving?
No. It stays the same.
Any factor that affects the genes in
a gene pool can change genetic
frequencies disrupting a
population’s genetic equilibrium
which results in the process of
evolution.
Occasionally, a mutation results in
a useful variation and the new
gene becomes part of the
population’s gene pool by the
process of natural selection.
What is genetic drift?
The alteration of allelic frequencies by chance
events, such as a catastrophic event that
eliminates many members of a species leaving
them with a limited amount of variation.
Bottleneck Effect
Why is genetic drift more common in
small populations or isolated groups
within a larger population?
Small or isolated populations have a smaller
gene pool so one event which eliminated
individuals (and their genes) is more evident.
What is gene flow?
The movement of individuals and their genes
How does it affect genetic
equilibrium?
It disrupts the equilibrium by
adding new genes to the pool.
Natural selection is usually
the most significant factor
that causes changes in
established gene pools.
What are the 3 types of natural
selection that act on variation?
Stabilizing
Directional
Disruptive
What is stabilizing selection?
Natural selection
that favors
average
individuals.
What is directional selection?
Natural selection
that favors one of
the extreme
variations of a trait.
What is disruptive selection?
Individuals in
either
extreme of a
trait’s
variation are
selected for.
This can lead
to speciation.
What might happen if significant
changes in the gene pool of a species
occur over time?
It could lead to the
evolution of a new
species.
What is a species?
Groups of organisms that
can interbreed to
produce fertile offspring.
What is speciation? What causes it?
The evolution of a new species.
It is caused when member of
similar populations no longer
interbreed to form fertile
offspring.
What is geographic isolation?
This occurs when a
physical barrier divides a
population.
For
example;
What is reproductive isolation?
What formerly interbreeding organisms can no
longer mate and produce fertile offspring.
Hybrid animals – have a more recent
common ancestor.
Just
Kidding
What are 2 types of reproductive
isolation?
1. Genetic material of the two populations grow
to become so different that fertilization
cannot occur.
2. Behavior changes – such as different mating
seasons.
What is polyploid
Any individual or species with a multiple of the
normal set of chromosomes (3n or 4n).
How does the rate of speciation by
polyploidy compare…
Polyploidy takes only one
generation.
What is gradualism?
The idea that species or organisms originate
through a gradual change of adaptations.
What is punctuated equilibrium?
Speciation occurring in short bursts followed by
long periods of genetic equilibrium.
What type of events could cause
punctuated equilibrium to occur?
Sudden environmental
changes or the introduction
of a competing species.
When speciation occurs “quickly” how
long does that mean?
About 10,000 years
or less.
Niche?
The role or position a
species has in its
environment; or the way a
species makes its living.
What is adaptive radiation?
When an ancestral species evolves into an array
of species to fit a number of diverse habitats.
Although adaptive radiation occurs
throughout the world, it is most
common on islands.
*Islands that were previously unpopulated by
the organism in question and has a variety of
available niches.
What is divergent evolution?
It is a type of adaptive radiation, where species
that were once similar diverge and evolve in
different directions.
What is convergent evolution?
A pattern of evolution in which distantly related
organisms evolve similar traits.
How does convergent evolution occur?
This happens when unrelated species occupy
similar niches which demand certain traits.