1. Evolutionary Mechanisms

2. 1. Types of Selection Directional selection Stabilizing selection
Disruptive selection
Sexual selection
Artificial selection

3. a) Directional Selection
Selection that favors an increase or decrease in the value of a trait from the current population average.
If a population of hummingbirds enters a habitat with longer flowers, longer bills will be selected for.
Common in artificial breeding
Strawberries are selected for bigger, sweeter fruit.

4. b) Stabilizing Selection
Selection against individuals exhibiting traits that deviate from the current population average.
If hummingbirds live in a habitat of medium length flowers, then medium length bills will be selected for.

5. c) Disruptive Selection
Selection that favors two or more variations of a trait that differ from the current population average.
Suppose only short and very long flowers are available to the hummingbirds….the medium billed hummingbirds would be selected against.

6. d) Sexual Selection
The favoring of any trait that enhances the mating success of an individual.
In many species, females choose males based on physical traits.
Bright colouration
Specific behaviours
Larger body size
Number of blue trinkets in their nest! (bowerbirds)

7. e) Artificial Selection
The selection by humans of animals, plants, or other organisms to breed together.
Artificial selection is also known as “selective breeding”
Breeders use artificial selection to ensure the continuation of desirable traits and to develop new varieties.

8. 2. Evolutionary Change without Selection
Genetic drift
Bottlenecks and the Founder Effect
The Hardy-Weinberg Principle
Biotechnology

9. a) Genetic Drift Changes to allele frequencies due to chance.
More pronounced in small populations.
Seneca army base deer

10. b) Bottlenecks
Genetic bottleneck – a dramatic reduction in population size resulting in genetic drift.
If hummingbirds are reduced to 50 hummingbirds they are unlikely to contain all the alleles found in the larger population.

11. c) Founder Effect
When a small number of individuals establishes a new population.
A small number of finches from South America established a founding population on the Galapagos Islands.

12. d) The Hardy-Weinberg Principle
In large populations, in which only random chance is at work, allele frequencies are expected to remain constant from generation to generation.

13. e) Biotechnology
Humans use technology to change the genetics of organisms in order to produce a desired trait.