1. Types of Natural Selection

2. Definitions..
Evolution is the change in a population’s genetic material (alleles) over generations.

3. Definitions..
Evolution is the change in a population’s genetic material (alleles) over generations.
A population is in genetic equilibrium if it’s not evolving

4. Definitions..
Evolution is the change in a population’s genetic material (alleles) over generations.
A population is in genetic equilibrium if it’s not evolving.
If the population’s allele frequencies stay the same year to year then it’s not evolving.

5. Hardy-Weinberg Genetic Equilibrium
Hardy-Weinberg equilibrium describes populations that are not evolving

6. Hardy-Weinberg Genetic Equilibrium
Hardy-Weinberg equilibrium describes populations that are not evolving
Genotype frequencies stay the same over time as long as certain conditions are met:

7. Hardy-Weinberg Genetic Equilibrium
Hardy-Weinberg equilibrium describes populations that are not evolving
Genotype frequencies stay the same over time as long as certain conditions are met:
Very large populations
No emigration or immigration
No mutations
Random mating
No natural selection

8. Natural Selection (3 Types)
Organisms best suited to their environment live to reproduce and pass on their genes
Acts on a phenotype
Varying types of selection

9. 1. Directional Selection
Individuals with a more extreme form of trait have higher fitness

10. Example
Suppose a new predator is released into the environment. Large fish are stronger swimmers and can get away. Draw a new curve showing what the histogram will look like after 200 years.

11. 1. Directional Selection
Individuals with a more extreme form of trait have higher fitness
Suppose termites in an area begin to build deeper nests. Anteaters with long tongues could more effectively prey on termites than those with short or average tongue length
Normal Distribution
Distribution after Selection

12. 2. Stabilizing Selection
Having average form of trait has highest fitness
Reduces extremes

13. Example
Suppose a new predator is released into the environment. Large fish are easily spotted by predators and small fish are not strong enough to swim from the predators. Draw a new curve showing what the histogram will look like after 200 years.

14. 2. Stabilizing Selection
Having average form of trait has highest fitness
Reduces extremes
Blue curve shoes variation after a new predator is introduced. Predator can easilty capture the large, visible lizards and the small slower lizards. Thus, selection against these extremes body types reduces the size range in lizards
Normal Distribution
Distribution after Selection

15. 3. Disruptive Selection
Individuals with either extreme trait has a higher fitness and most likely results in two new species

16. Example
Suppose a new predator is released into the environment. Large fish are strong swimmers and can get away from predator. Small fish can hid in the cracks and crevices of the rocks. Draw a new curve showing what the histogram will look like after 200 years.

17. 3. Disruptive Selection
Individuals with either extreme trait has a higher fitness and most likely results in two new species
Divergent Evolution
The white limpets blend in with barnacles on rocks. On bare rocks, dark-shelled limpets blend in. However, the tan colored limpets are easy to spot by birds.
Normal Distribution
Distribution after Selection