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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.
1. Mutations
One type of mutation at the
level of the gene.
One type of mutation at the
level of the chromosome.
-occur randomly
- can be beneficial, neutral, or harmful in
their effects
Venom-like proteins
first appeared about 200 million years ago
2. Gene Flow or Migration
• is the transfer of alleles or genes from one
population to another.
• This makes separate populations more similar
Ex. Gene flow in plants
– wind-dispersed pollen
Gene Flow or Migration
• 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:
a. Genetic Bottleneck –
allele frequency is altered due to
a population crash.
-Only the survivors will
reproduce offspring
b. The Founder
• occurs when a small number of individuals from one population found a
new population that is reproductively isolated from the original one.
Endangered Species Are in the Narrow Portion of a Genetic
Bottleneck and Have Reduced Genetic Variation
4. 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
• causing an alteration in allele
frequency over time
• leads to a consequent increase in
• The production of healthy, fertile
offspring results in VARIATIONS in
the gene pool.
Darwin’s Finches and the Theory of Evolution of Natural Selection
Case Study
Peter and Mary
Grant and their
observed how
beak depth, a
significant trait
for feeding
success, varied
in populations
Beak depth is a genetically
determined trait.
5. Recombination
-Genetic material combined during
sexual intercourse
-Crossing over
-Enormous diversity in species
-recombination or shuffling of
-creates new allele combinations
in the gametes (sex cells)
Crossing Over