1. Evolution as genetic change

2. Evolution: Genetic definition
Evolution is any change in the relative frequencies of alleles in the gene pool of a species
Sexual reproduction alone cannot cause such a change

3. Natural selection on single gene traits
Harmful mutations
Fewer copies of the allele are passed on because the individual does not survive or does not reproduce
Allele becomes less common in the population

4. Natural selection on single gene traits
Helpful mutations
Carriers of the allele produce more offspring that survive than non-carriers
Relative frequency of this allele increases in a few generations
 An allele with no negative effects will be found after several generations in nearly all members of the species

5. Natural selection on polygenic traits
Variation of polygenic traits is a normal distribution
Fitness of individuals near each other in the distribution is similar
BUT can vary considerable from one side of the curve to the other

6. Natural selection on polygenic traits
Natural selection can affect this distribution in three ways:
1. Stabilizing selection
2. Directional selection
3. Disruptive selection

7. Stabilizing selection
Organisms near the center of the curve are more fit than those at the ends
Look at figure on page 489
Example: human baby weight at birth
Evolution is minor or absent

8. Directional selection
Organisms at one end of the curve have higher fitness than those in the middle or the other end
Entire curve moves as the trait changes
Evolution occurs, change in allele frequency
Example: finches

9. Disruptive selection
Organisms at the ends of the curve have higher fitness than those in the middle
Single curve can split into two curves if the selective pressure is high
Example: insects that resemble poisonous insects

10. Other mechanisms of evolution
Role of chance
In small population allele frequency can change due to chance
Random change in allele frequency is called genetic drift
Bottleneck and founder effects
Look at figure on page 490 for example

11. Speciation (1) A new species evolves when:
A population changes enough (genetic changes) so that breeding cannot occur between members of the original population and the changing population

12. Speciation (2)
One major way is when two populations are isolated from each other geographically
Other ways:
Behavioral isolation
Temporal isolation

13. Pace of evolution Gradualism Punctuated equilibrium
Evolutionary change takes long periods of time
Darwin proposed this
Punctuated equilibrium
Evolution proceeds rapidly followed by periods of stability, then more evolution, then stability
Modern view, along with gradualism

14. How do you test if evolution is happening?
Scientific method again…..
Hypothesis is evolution is not happening (= allele frequencies are not changing)
Measure allele frequencies over time and see if they change or not
Five conditions can result in allele frequency change

15. Hardy Weinberg principles
The five condition are:
Non random mating
Immigration or emigration
Small population sizes
Mutations
Natural selection