1. EVOLUTIONARY MECHANISMS

2. Evolutionary Change
Gene pool: the genetic information for an entire population
Allele frequency: the proportion of gene copies of a given allele in a population.
Evolution occurs when the allele frequencies of a population change over time.

3. 1. Small vs. Large Populations
Genetic Drift: When a population is small, chance fluctuations can cause changes in allele frequencies.
Could become the dominant trait of the species.
Could be wiped out.

4. 1. Small vs. Large Populations
Bottleneck effect: drastic reduction in numbers, small sample of alleles survives, new generation different from original
Northern elephant seal (reduced to 20 individuals in 1890s…)

5. 1. Small vs. Large Populations
Founder effect: a few individuals leave to establish a new population
Ex. Seeds/insects carried by wind, birds to another island

6. More Founder Effect Examples
Self-pollinating plants
Amish community in Pennsylania (30 emigrants from Switzerland, 1720)
Ground finches in the Galapagos ( , a new population developed – discovered by scientists at Queen’s)

7. 2. Random vs. Non-random Mating
When mating opportunities are non-random, individuals that are preferred as mates will pass on their alleles in greater numbers than less preferred mates.

8. 3. Genetic Mutations
Genetic mutations create new alleles or change an existing one into another, thereby changing the frequency of both alleles.
Gene duplications are the main source of new genetic material, as extra copies they are free to mutate with less likelihood of causing harm.
Mutations occur as 1 in in a small genome (bacteria) to about 1 or more per gamete in larger genome.

9. 4. Migration
When individuals migrate, this alters the allele frequency of both the population it left and the one it joined.
Gene flow: movement of alleles from one population to another.
Tends to reduce differences between populations

10. 5. Natural Selection
When natural selection occurs, individuals with certain alleles have greater reproductive success than others do, thereby increasing the relative frequency of their alleles in the next generation.
Harmful genes selected against
Useful genes accumulate