Download Mechanism of Evolution

Mechanisms of Evolution
How does evolution work?
Targets:
10. Explain the significance of gene pools in understanding
evolution.
11. Tell how genetic drift, gene flow, mutation, and natural
selection contribute to changes in a gene pool.
Mechanism of Evolution
• cause generation-to-generation changes in allele
frequency within populations.
• Population:
• a group of interbreeding organisms
• in a specific location
• specific time.
• Allele frequency: the frequency of a particular
allele in the population.
Changes in allele frequency within populations drive
evolution.
The Genetic Basis of Evolution
Gene Pools
are all of the alleles (alternate forms of genes) in
all of the individuals that make up a population.
What Drives Evolution?
There are 5 forces of change.
Only natural selection
makes a population better
adapted (more fit) to its
environment.
Mutations
One type of mutation at the
level of the gene.
One type of mutation at the
level of the chromosome.
Mutations
-occur randomly
- can be beneficial, neutral, or harmful in
their effects
Venom-like proteins
first appeared about 200 million years ago
Gene Flow or Migration
• is the transfer of alleles or genes from one
population to another.
• This makes separate populations more similar
genetically.
Ex. Gene flow in plants
– wind-dispersed pollen
Gene Flow or Migration
GENETIC DRIFT
• A change in the population because of a
random event, such as a catastrophe
• The smaller the population, the less
genetic variety it has.
• 2 Types:
Genetic Bottleneck –
allele frequency is altered due to
a population crash.
-Catastrophe
-Only the survivors will
reproduce offspring
.
Endangered Species Are in the Narrow Portion of a Genetic
Bottleneck and Have Reduced Genetic Variation
2. The Founder
Effect
• occurs when a small number of individuals from one population found a
new population that is reproductively isolated from the original one.
The Founder Effect is Another Variation of Genetic Drift
The South Atlantic island of Tristan da Cunha was colonized by 15 Britons in 1814,
one of them carrying an allele for retinitis pigmentosum. Among their 240
descendents living on the island today, 4 are blind by the disease and 9 others are
carriers.
Natural Selection
Natural selection leads to adaptation – an
increase in the fitness of a population in a
particular environment.
Successful (adaptive)
genotypes become more
common in subsequent
generations, causing an
alteration in allele
frequency over time that
leads to a consequent
increase in fitness.
The production of healthy,
fertile offspring results in
changes
in the gene pool.
.
Darwin’s Finches and the Theory of Evolution of Natural Selection
Case Study
Peter and Mary
Grant and their
colleagues
observed how
beak depth, a
significant trait
for feeding
success, varied
in populations
experiencing
climactic
variations.
Beak depth is a genetically
determined trait.
Nonrandom mating
-individuals of one genotype
reproduce more often with each
other.
-May be due to Ethnic or
religious preferences Isolated
communities Cultures in which
consanguinity (marriages between
relatives – cousins) is more
prominent
-EX: The males of some
bird species must make
ELABORATE NESTS to lure in
potential female partners.