1. Measuring Evolutionary Change Over Time
Population Genetics
Measuring Evolutionary Change Over Time

2. I. Vocabulary Review
Population: a collection of individuals of the same species in a given area whose members can breed with one another.
Species: a group of individuals that look similar and whose members are able to produce fertile offspring.
Natural Selection: a process in nature that results in the most “fit” organisms reproducing.
Genetic Drift: A process in nature that results in a reduction in genetic variation.
Evolution: occurs when gene frequencies in a population change between generations. Caused by natural selection, genetic drift, gene flow, mutations or a combination of them.

3. II. Measuring Evolution
Phenotypic Measurement
Definition:
The process of using physical characteristics to identify similarities and differences among organisms over time
Example:
The Grant’s used tools to measure differences in beak dimensions
What are the limitations of using this method to measure evolutionary change?

4. II. Measuring Evolution
B. Genotypic Measurement
Definition:
The process of using genes and allele frequencies to identify similarities and differences among organisms over time
Example:
The Hardy-Weinberg Principle
What are the benefits of using this method to measure evolutionary change?

5. III. Genetics Vocabulary
Trait:
An inherited physical characteristic
Gene:
An inherited segment of DNA on a chromosome that codes for a trait
Allele:
One of a number of different forms of a gene for a particular trait
Homozygous:
Having 2 identical alleles for a trait (AA or aa)
Heterozygous:
Having 2 different alleles for a trait (Aa)
Genotype:
The genetic make-up of an organism
Phenotype:
The physical traits of an organism
Dominant:
An allele that is always expressed in the phenotype (A)
Recessive:
An allele that is only expressed in the phenotype when homozygous (a)

6. Rr rr Rr rr Review of Simple Punnett Squares
Possible alleles from male gametes
Possible alleles from female gametes Rr rr
Genotypic Ratios in Offspring Generation
50% - Rr 50% - rr Rr rr

7. IV. Genetic Equilibrium
A population in which allele frequencies do not change from generation to generation.

8. V. The Hardy-Weinberg Principle
A. In 1908, a British mathematician, Godfrey Hardy, and a German physician, Wilhelm Weinberg, outlined the conditions necessary for genetic equilibrium
The Hardy-Weinberg Principle states that a population will remain in genetic equilibrium if all of the following conditions are met:
No mutations occur
Individuals neither enter nor leave the population through migration (no gene flow)
Population is large (no genetic drift)
Individuals mate randomly (no genetic drift)
Natural Selection does not occur
If even one of these conditions does not hold true, allele frequencies in the population may change and evolution will occur.

9. VI. Measuring Evolution using Allele Frequencies
Population of Organisms
Gene Pool
Hardy-Weinberg conditions are met:
no mutation
no migration
large population size
random mating
no natural selection
One or more Hardy-Weinberg conditions are NOT met:
Allele Frequencies do NOT change
Allele Frequencies change
Genetic Equilibrium
Genetic Disequilibrium
Evolution will occur
Evolution will NOT occur

10. VI. Measuring Evolution using Allele Frequencies
B. The Hardy-Weinberg Mathematical Formulas
p + q = 1 (used to measure allele frequencies)
If ‘A’ and ‘a’ are alleles for a particular gene and each individual has two alleles, then p represents the frequency of the A allele
If ‘A’ and ‘a’ are alleles for a particular gene and each individual has two alleles, then q represents the frequency of the a allele
p2 + 2pq + q2 = 1 (used to measure genotype frequencies)
p2 represents the frequency of the homozygous dominant condition (AA)
2pq represents the frequency of the heterozygous condition (Aa)
q2 represents the frequency of the homozygous recessive condition (aa)