1) Mutations, gene flow, and recombination increase genetic variation in populations by introducing new alleles. 2) Natural selection and genetic drift decrease variation by eliminating less adapted alleles or reducing population size. 3) Convergent evolution occurs when unrelated species evolve similar traits due to common environmental pressures. Divergent evolution happens when related species evolve different traits in different environments, possibly leading to speciation. Vestigial structures provide evidence of evolution from ancestral forms.

1. EVOLUTION AND ADAPTATION
Factors Affecting Genetic Variation

2. Factors which increase variation
1: Mutations
• Permanent change to the nucleotide sequence,
genes or chromosomes of an organism
• May be positive, negative or neutral
• Main source of new alleles in a population
• May occur randomly or result from exposure to an
environmental stimuli (mutagen)

3. Factors which increase variation
2: Gene Flow
• Transfer of alleles or genes from one population to another (of the same
species) by migration
• Immigration: Individuals join a new population – adds alleles to the gene
pool
• Emmigration: Individuals leave current population – gene pool loses alleles
• Reduces specialization to the environment
• Prevents divergence of gene pools and speciation

5. Factors which increase variation
3: Recombination
• Crossing Over: During meiosis sections of
homologous chromosomes align and swap
segments of genes
• Meiosis results in the production of gametes that
are genetically different from each other and the
parent

6. Factors which decrease variation
1: Natural Selection
• Survival of the fittest leads to
accumulation of favourable traits
• Fewer non-adaptive alleles remain in
the population

7. Factors which decrease variation
2: Genetic Drift
• Random change in the variation or allele frequency
of a population
• Most common in small populations
A) Bottleneck Effect
• Event drastically reduces population size
• Survivors are not necessarily “fittest” but live by
chance and pass on genes
• Bottleneck event: natural disaster, disease,
habitat destruction etc.

8. Factors which decrease variation
2: Genetic Drift cont’d
B) Founder Effect
• Few individuals leave original population and begin a new
population
• New population contains only alleles carried in by founders

9. Factors which decrease variation
3: Non-Random Mating
• Some individuals are more likely find a successful mating partner, therefore
more of their alleles will be present in subsequent generations
• Proximity – Easier to mate with nearby organisms
• Competition – “Fitter” organisms are more likely to out compete other
possible mating partners and pass on their traits

11. EVOLUTION AND ADAPTATION
Evolutionary Pathways

12. Evolutionary Pathways:
Convergent Evolution
• Occurs when unrelated organisms evolve similar traits in response to
similar selective pressures
• Produces analogous structures – structures with same function from
different evolutionary origins

13. Evolutionary Pathways:
Convergent Evolution
Example:
Dolphin (mammal) Shark (fish) Ichthyosaurus (reptile)
What were the selective pressures acting on each of these organisms that led to the evolution o
such similar body plans?

14. Evolutionary Pathways:
Convergent Evolution
Example:
Hawk (bird) Bat(mammal) Bee (insect)
What were the selective pressures acting on each of these organisms that led to the evolution o
such similar body plans?

15. Evolutionary Pathways:
Divergent Evolution
• Occurs when closely related organisms evolve
very different traits in response to diverse
selective pressures
• May be the result of disruptive selection
• Leads to speciation
• Produces homologous structures – structures
with different functions arising from a common
ancestor

16. Evolutionary Pathways:
Vestigial Structures
• Remnants of a structure that had a function in an ancestor
but no longer does in the evolved organism.
Examples:
• Appendix – used to be for digestion
• Tail bone
• Snake hips – pelvis bone but no legs
• Chickens have gene for teeth but no teeth