1. Mechanisms of Evolution

2. 1. Mutation Randomly introduces new alleles into a population.
Changes allele frequencies

3. 2. Gene Flow (Migration)
Occurs between 2 different interbreeding populations with different allele frequencies
May change allele frequencies in either or both populations
Population A
Population B

4. 3. Non-random mating
Individuals in a population. select mates, often on the basis of their phenotypes
Not every individual will have an equal opportunity to mate.
 If individuals prefer other individuals that are similar to themselves, e.g. tall people like tall people,  then homozygosity of alleles is favoured

5. Non-Random Mating: Inbreeding
As homozygous becomes more common, harmful recessive alleles more likely to be expressed
Pure-bred animals have higher incidence of deformities and health problems
Eg. Royal families
Eg. Shar-pei dogs’ wrinkles enhanced through inbreeding

6. 4. Genetic drift
Random change in genetic variation from generation to generation due to chance
More common in smaller populations
Changes frequency of alleles

7. The Bottleneck Effect
Starvation, disease, natural disasters and severe weather can quickly reduce sizes of large populations.
Survivors likely have a fraction of the alleles that were present before the reduction
Gene pool loses diversity

8. The Founder Effect
Few individuals from a large population leave to establish a new population
Eg. Amish (descendants of about 30 people from Switzerland in 1720)

9. 5. Natural Selection
Result of the environment selecting for individuals with certain traits that make them better suited to survive and reproduce
Over many generations, frequency of alleles of many different genes may change, resulting in significant changes