Download Mechanisms of 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.
Recombination
1. 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
2. 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
3. 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:
a. Genetic Bottleneck –
allele frequency is altered due to
a population crash.
-Catastrophe
-Only the survivors will
reproduce offspring
.
b. 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.
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
generations,
• causing an alteration in allele
frequency over time
• leads to a consequent increase in
fitness.
• 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
colleagues
observed how
beak depth, a
significant trait
for feeding
success, varied
in populations
experiencing
climactic
variations.
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
genes
-creates new allele combinations
in the gametes (sex cells)
Crossing Over
Chromosomes