1. Evolution of Populations

2. Genetic Variation mutations genetic shuffling Natural selection
 allele frequencies changes
 evolution

3. Example Red lizards Black lizards more visible to predators
less likely to survive and reproduce
allele for red coloring become rare
Black lizards
absorb more sunlight  warm up faster
move faster to feed and avoid predators
produce more offspring
Alleles for black become common

4. Natural Selection on Polygenic Traits
Direction Selection: individuals at one end of the curve have higher fitness
beak size & thickness

5. Beak Size in Birds

6. Natural Selection on Polygenic Traits
Stabilizing Selection - individuals near the curve’s center have higher fitness
Size of baby at birth

7. Natural Selection on Polygenic Traits
Disruptive Selection - individuals at the upper and lower ends of the curve have higher fitness
Environment with few medium size seeds

9. Genetic Drift Small population
individuals with a particular allele may leave more descendants by chance
With more chance occurrences
an allele to become common in a population.
Founder Effect: allele frequencies change due to a subgroup’s migration

10. Genetic Drift

11. Hardy – Weinberg Principle
allele frequencies remain constant unless factor(s) change frequencies
Requirements of Hardy-Weinberg
random mating
very large population
no movement in or out of the population
no mutations
no natural selection

12. Speciation: new species formation
Reproductive Isolation: 2 populations cannot interbreed and produce fertile offspring
Behavioral Isolation
Different courtship rituals
Different reproductive strategies
Geographic Isolation
geographic barriers; rivers, mountains
Temporal Isolation
reproduce at different times of the year