1. Shaping evolutionary theory Slide 1
Chapter 15 Section 3
Shaping evolutionary theory
Slide 1

2. slide 2 What is an allele again?
It’s an alternative form that a single gene may have for a particular trait.
Pictured are two homologous chromosomes. Each chromosome has the same type of gene at the same spot. Different versions of this gene are called alleles. These two genes make up this organisms genotype for the trait of flower color.

3. Slide 3 What does it look like when there’s no evolution?
Population of Owls
Number of each allele in Generation #1
F: 3
f: 3
Ratio F:f 3:3 or 1:1
Generation #1 ff FF Ff
Number of each allele
in Generation #2
F: 6
f: 6
Ratio F:f 6:6 or 1:1
Generation #2 ff Ff FF

4. Slide 4What would NO evolution look like?
When there’s no evolution, allelic frequencies remain constant.
This is called being in genetic equilibrium.
This is the basis for the Hardy-Weinberg principle which describes what conditions need to be met in order for NO evolution to occur and a population to remain in genetic equilibrium.
Ex: although the number of owls doubled, the ratio of gray to red owls is the same and the allelic frequencies are the same.

5. Slide 5
To be in equilibrium, the population must meet 5 conditions (no mechanisms of evolutionary change):
1. no genetic drift
2. no gene flow
3. no mutation
4. mating must be random
5. no natural selection
*populations in nature might meat some of these requirements, but hardly any population meets all 5 conditions for long periods of time.

6. Slide 6: Mechanisms of Evolution: genetic drift
Genetic Drift: Any change in the allelic frequencies (# of each kind of allele in the population) that results from chance.
These effects are more pronounced in smaller populations.

7. Slide 8: Mechanisms Video: 5 Fingers of Evolution
Pinky- Shrinking Population (aka genetic drift- which is more pronounced in a smaller population- founder effect & bottleneck
Ring- Nonrandom Mating
Middle- Mutation
Pointer- Gene Flow
Thumb (up/down)- natural selection

8. Slide 7: Mechanisms of Evolution: genetic drift continued
Founder Effect- small sample of a population settles in a location separated from the rest of the population.
Alleles that were uncommon in the original population might become common in the new population
Bottleneck- population declines to a very low # then rebounds.

9. Slide 9 Mechanisms of Evolution: Gene Flow
Mechanism of evolution
Can occur during migration of individuals from one population to another
When the migrating individuals breed with the new population, they contribute their genes to the gene pool of the local population
Makes gene pools of the same species more similar to one another
Ex: wind carrying seeds from parent population to another population,
Ex: animals driven off of herd join a new population

10. Slide 10: Mechanisms of Evolution: Nonrandom Mating
Mechanism of Evolution
What would completely random mating look like?
Individuals regardless of environment, heredity, or social interaction. Potential mates have an equal chance of being selected. As long as mating was random and no other mechanisms of evolution were happening, no evolution would occur in this population.
The result of nonrandom mating is that some individuals have more opportunity to mate than others and thus produce more offspring (and more copies of their genes) than others. It is simply easier to mate with a nearby individual, as opposed to one that is farther away. Also, especially in animals, individuals compete for mates and active selection of mating partners occurs. This goes directly against the concept of randomness.

11. Slide 11: Mechanisms of Evolution: Mutation
Mechanism of evolution
Mutation, a driving force of evolution, is a random change in an organism’s genetic makeup, which influences the population’s gene pool.
Mutations give rise to new alleles; therefore, they are a source of genetic variation in a population.
Mutations may be harmful or benign, but they may also be beneficial.

12. Slide 12: Mechanisms of Evolution: Natural Selection
Mechanism of evolution
Individuals in a population are not equally adapted to the environment
Best traits survive
Types of natural selection
Directional
Stabilizing
Disruptive
Sexual

13. Slide 13 Graphs of Natural Selection