1. Evolution of Populations
Microevolution

2. Variations in Gene Pools
Microevolution: evolution on the smallest scale – generation to generation change in the frequencies of alleles in a population
Gene Pool: consists of all the genes that are present in a population
Relative Frequency: The number of times an allele occurs in a gene pool compared with the number of times other alleles for the same gene appear

3. Relative Frequencies of Alleles
Sample Population
Frequency of Alleles
allele for brown fur
allele for black fur
48% heterozygous black
16% homozygous black
36% homozygous brown

4. Sources of Genetic Variation
Mutations: a change in the genetic sequence. Some may produce changes in the phenotype that result in better fitness.
Gene Shuffling: which results from the shuffling of gametes and sexual reproduction; produces many different combinations of genes.

5. Single Gene & Polygenic Traits
A single gene trait is controlled by 1 gene with 2 alleles. Ex. Widow’s peak.
Polygenic Traits: Each gene has two or more alleles which results in many possible genotypes and phenotypes.
Frequency of phenotype
Widow’s peak
No widow’s peak
Frequency
Phenotype Height

6. Natural Selection of Single-gene Traits
Can lead to change in allele frequencies and thus evolution.
Initial Pop.
Gen. 10
Gen. 20
Gen. 30
80% Brown
80%Brown
70% Brown
40% brown
10 % red
0% red
10% black
20% black
30% black
60% black

7. Genetic Drift The random change in allele frequency.
In a small population, individuals that carry a particular allele may leave more descendants than other individuals, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become more common.

8. Genetic Drift Founder’s Effect: Allele frequencies change
Sample of
Original Population
Descendants
Founding Population A
Founding Population B
Founder’s Effect: Allele frequencies change
as a result of the migration of a small subgroup.

9. Evolution Versus Genetic Equilibrium
Hardy-Weinberg Principle (1908) states that allele frequency in a population will remain constant unless one or more factors cause those frequencies to change.
Genetic Equilibrium: allele frequencies remain the same.

10. Five Conditions of Hardy-Weinberg
Random mating – no sexual selection
Large population – no genetic drift
No migrations – immigration or emigration
No mutations
No natural selection
STOP

11. Natural Selection on Polygenic traits
Can affect the distribution of phenotypes in three ways: direction, stabilizing, or disruptive.

12. Graph of Directional Selection
Key
Directional Selection
Low mortality, high fitness
High mortality, low fitness
Food becomes scarce.
The environment favors one extreme

13. Graph of Stabilizing Selection
Key
The average
Organism is
More fit
Low mortality, high fitness
High mortality, low fitness
Selection against both extremes keep curve narrow and in same place.
Percentage of Population
Birth Weight

14. Graph of Disruptive Selection
Largest and smallest seeds become more common.
Key
Low mortality, high fitness
Population splits into two subgroups specializing in different seeds.
Number of Birds in Population
Number of Birds in Population
High mortality, low fitness
Beak Size
Beak Size
Organisms with either of the two
Extremes are better fit.