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Evolution of
Populations
16.1 pp. 299-302
Random mating
requires no sexual
selection, a form of
natural selection.
Hardy-Weinberg Equilibrium
describes populations that
are NOT evolving, allele
frequency is in equilibrium
5 conditions necessary:
1. No mutations
2. No migration
3. No natural selection
4. Large population size
5. Random mating
Evolution of
Populations
16.2 pp. 304-308
Common mutations:
S
Disruption of Genetic
Equilibrium
1. Mutation = mistake in
copying the genetic code
1. Can be single letters or
entire genes
2. Can be good or bad
3. Natural selection can only
act on those genes that are
expressed so recessive genes
can take a long time to be
removed from a population
Evolution of
Populations
16.2 pp. 304-308
Disruption of Genetic
Equilibrium
2. Migration = individuals
moving into or out of a
population (adds or removes
genes)
Immigration =
individuals move into
the pop.
Emigration = individuals
move out of pop.
Evolution of
Populations
16.2 pp. 304-308
Disruption of Genetic
Equilibrium
3. Genetic Drift (small pop.)=
loss of alleles in small
populations (genes drift
away) due to random events
Evolution of
Populations
16.2 pp. 304-308
Disruption of Genetic
Equilibrium
4. Non random mating =
mating is rarely random,
affected by:
- location
- timing
- kinship
- sexual selection
Evolution of
Populations
16.2 pp. 304-308
Disruption of Genetic
Equilibrium
5. Natural selection =
environment favors certain
traits over others
- increased fitness for
selected traits
- individuals with those
traits survive better,
pass on those genes
Evolution of
Populations
16.2 pp. 304-308
Types of Natural
selection:
Directional selection =
population shift in
direction of selection
Examples:
Disruption of Genetic
Equilibrium
Evolution of
Populations
16.2 pp. 304-308
Types of Natural
selection:
Disruptive Selection =
Selection toward the
extremes (disruption
of normal distribution)
-often new species
Examples:
Disruption of Genetic
Equilibrium
Evolution of
Populations
16.2 pp. 304-308
Types of Natural
selection:
Stabilizing Selection =
Selection toward the
average
- Focusing of traits
Disruption of Genetic
Equilibrium
Evolution of
Populations
16.2 pp. 304-308
Types of Natural
selection:
Sexual Selection:
Again, choosing a
mate directly affects
fitness
Disruption of Genetic
Equilibrium
Western Grebes (mate for
life):
https://www.youtube.com/w
atch?v=-O8_DMfPJus
Sharptail Grouse:
https://www.youtube.com/w
atch?v=zvoZkjuYD54