1. Mechanisms for Evolution1

2. Population Genetics: Measuring the
changes in alleles within a population
over generations.
Causes of Variation:
A. Mutations
B. Crossing -over during meiosis
C. Independent Assortment
D. Random fusion of gametes

3. Populations evolve, not individuals
Individuals cannot evolve a new phenotype in response to the environment.

4. Gene pool -the genetic composition of a population; (all of the alleles of a population’s genes for a particular trait)
Allele frequency - the relative frequency of a particular allele in a population (% or fraction) for a particular trait.

5. Read example in notes and
Refer to fig on page 394.

6. a useful variation, produce new alleles for traits.
Factors that disrupt genetic equilibrium:
1. Mutations that become
a useful variation, produce
new alleles for traits.

7. 2. Gene Flow (migration) - the transport of genes when individuals enter (Immigration) and leave (Emigration) populations 7

8. 3. Genetic Drift – Allele frequency
changes as a result of
chance events
like storms, floods, fires, or other acts
of nature
Changes have a greater effect on small populations with small gene pools
ex. What if a fire killed off most of the black mice in the population?

9. 4. Nonrandom mating (Sexual Selection)
Nonrandom Mating: Mating based on preferences
Most species do not mate randomly, but rather choose a mate based on desirable traits
Example: a female may choose a mate based on male size, color, or ability to gather food.

10. 5. Natural selection acts on variations that increase or decrease an organism’s chance for survival
3 different types of natural selection on variation

11. Stabilizing selection
natural selection favors average individuals in a population
Average sized salmon are “selected for”

12. Directional selection
natural selection favors small or large extreme variation of a trait
woodpeckers with long beaks are “selected” over those with short or normal beaks

13. Disruptive selection
individuals with either extreme of a trait’s variation are selected for
dark and light limpets over normal (tan) limpets (sea snail) 13

14. Peppered Moth
There are two variations in color of peppered moths, light and dark.

15. Prior to the industrial revolution, tree trunks were light colored.
Predators were more likely to pick the dark moths. As a result, the moth population was primarily light.

16. http://www. globalchange. umich
es_by_Unit/Unit_3a_files/image004.jpg

17. After the industrial revolution, trees were covered in soot making them dark.
Now, predators were more likely to pick the light moths. As a result, the population shifted from being primarily light to primarily dark.

18. http://www. globalchange. umich
es_by_Unit/Unit_3a_files/image004.jpg

19. What type of selection is this an
example of ?

20. Sexual Selection: