1. The Genetic Basis of Evolution
Darwin knew heredity was vital to evolution. His ideas:
Random changes appear in a population
Individuals vary in their traits
Adaptive value of changes depends on environmental context.

2. Mutation Ultimate source of variation
Rate of mutation in eukaryotes is 1 in DNA base pairs, on average.
Many mutations are neutral, but others are not; these are the ones subject to natural selection.
Low rate of mutation = slower ability of a species to adapt
High rate of mutation = more variability in the species, and faster ability to adapt.

3. Occurs when populations are isolated.
Genetic Drift
Occurs when populations are isolated.
Mutation continues to occur within each population, as well as inbreeding.
Over time, each population accumulates different traits; they ‘drift’ away from the phenotype they once shared and become unique.

4. Isolating Mechanisms Geographic Behavioural Ecological Reproductive
Two populations, isolated long enough from one another, and subject to Genetic Drift, will become separate species.
This is Speciation.

5. Defining a Species:
A Species is any group of potentially or actually interbreeding individuals, capable of producing viable, fertile offspring.
The Eastern Meadowlark & Western Meadowlark look similar, & their geographic ranges even overlap. However, they are reproductively isolated from one another: their songs are different, & prevent mating.

6. Directional: One extreme is more adaptive & selected for.
Selection Mechanisms
Stabilizing: keeps things the same; the intermediate phenotype is most adaptive & selected for.
Disruptive: Leads to change & speciation; intermediate is selected against, extremes are favoured.
Directional: One extreme is more adaptive & selected for.

7. Selection Mechanisms

8. Founder Effect
One part of a population breaks off from the main population & establishes a new group elsewhere. For example:
Some female deer follow a young male to a new territory.
Songbirds forced into new habitats
Human Colonists

9. Founder Effect Can lead to unique genetic hallmarks:
Polydactyly among the Amish
Tay Sachs disease among Central European Jews
Wild Horses in North America

10. Genetic Bottlenecks
Like founder effect, but after some extreme environmental change
Drastic reduction in population
Limited genome left behind.
Examples:
Overhunting of Eur. & N.Am. Bison
Survivors of natural disasters
Toba catastrophe, 70 kya, for humans?

11. Genetic Bottlenecks

12. Genetic Bottlenecks