Mechanisms of Evolution

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

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

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

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

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

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

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)

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