Download Mechanisms of evolution pp

Mechanisms
of Evolution
Evolution – a change in the population’s
gene pool over time
These changes can be caused by:
Genetic drift
Natural selection
Genetic Drift – a change in the gene pool
caused by chance
Ex: A natural disaster removes all but a few
members of the population.
Result: The remaining individuals have a smaller
gene pool, some variations may have been lost.
The next generation will lack those variations.
The gene pool has changed,
evolution has occurred.
Migration will also change the gene pool.
• Immigration will add genes to the gene pool
• Emigration will decrease the gene pool
Natural Selection1. Overproduction occurs in all species
2. Variations occur in all species
3. Struggle for survival- resources are limited,
not all born will survive
4. Survival of the fittest- those best adapted to
their environment will survive and
reproduce.
How do variations occur?
• Viruses alter a cell’s DNA
• Chemicals and radiation can cause mutations
If this occurs in the egg or sperm
it will be passed to the offspring
• Sexual reproduction causes a mixing of genes
Fitness: ability of an individual to
survive and reproduce
- central to the process of Evolution
- individuals with low fitness either
die or produce few offspring
Adaptation: Inherited characteristic
that increases an organisms chance
for survival
Ex: Speed, Camouflage, Claws, etc.
Evolution is driven by environmental change.
As the environment changes, different
adaptations will increase fitness.
Adaptations that decrease fitness will
eventually die out of the gene pool.
Evolution of
pesticide
resistance in
response to
selection
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