Lesson 4 - Mechanism of Evolution

Question 1

Microevolution

Answer 1

A change in a population’s gene pool over a succession of generations.

Evolutionary changes in species over relatively brief periods of geological time.

Five Mechanisms of Microevolution

1. Genetic drift:

Change in the gene pool of a small population due to chance.

Two examples:
- Bottleneck effect
- Founder effect

2. Gene Flow:

The gain or loss of alleles from a
population by the movement of individuals
or gametes.

Example:
- Immigration or emigration.

3. Mutation:

A change in an organism’s DNA that creates a new allele.

4. Non-random mating:

The selection of mates is not by chance.

5. Natural selection:

Differential reproduction.

Question 2

Bottleneck Effect

Answer 2

Genetic drift (reduction of alleles in a population) resulting from a disaster that drastically reduces population size.

Examples:
1. Earthquakes
2. Volcanoes

Question 3

Founder Effect

Answer 3

Genetic drift results from the colonization of a new location by a small number of individuals.

Results in a random change of the gene pool.

Example:
- Islands (first Darwin finch)

Question 4

Natural Selection: Modes of Action

Answer 4

Natural selection has three modes of action:

1.
Stabilizing selection

Acts upon extremes and favours the intermediate.

2.
Directional selection

Favours variants of one extreme.

3.
Diversifying selection

Favours variants of opposite extremes.