Population Genetics Measuring Evolutionary Change Over Time

I. Vocabulary Review A. Population: a collection of individuals of the same species in a given area whose members can breed with one another B. Species: a group of individuals that look similar and whose members are capable of producing fertile offspring C. Natural Selection: a process in nature that results in the most fit organisms surviving. Caused by deterministic factors. D. Genetic Drift: A process in nature that results in the “lucky” surviving. Caused by stochastic factors. E. Evolution: occurs when variation(s) within a population becomes more or less common over time, measured in future generations. Caused by natural selection, genetic drift or both.

II. Measuring Evolution A. Phenotypic Measurement 1. Definition: The process of using physical characteristics to identify similarities and differences among organisms over time 2. Example: The Grant’s used tools to measure differences in beak dimensions What are the limitations of using this method to measure evolutionary change?

II. Measuring Evolution B. Genotypic Measurement 1. Definition: The process of using genes and allele frequencies to identify similarities and differences among organisms over time 2. Example: The Hardy-Weinberg Principle What are the benefits of using this method to measure evolutionary change?

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)

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

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

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 B. The Hardy-Weinberg Principle states that a population will remain in genetic equilibrium if all of the following conditions are met: 1. No mutations occur 2. Individuals neither enter nor leave the population through migration 3. Population is large 4. Individuals mate randomly 5. Natural Selection does not occur C. If even one of these conditions does not hold true, allele frequencies of the population may change and evolution will occur.

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 Allele Frequencies do NOT change Genetic Equilibrium Evolution will NOT occur One or more Hardy-Weinberg conditions are NOT met: Allele Frequencies change Genetic Disequilibrium Evolution will occur

VI. Measuring Evolution using Allele Frequencies B. The Hardy-Weinberg Mathematical Formulas 1. 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 2. p 2 + 2pq + q 2 = 1 (used to measure genotype frequencies) p 2 represents the frequency of the homozygous dominant condition (AA) 2pq represents the frequency of the heterozygous condition (Aa) q 2 represents the frequency of the homozygous recessive condition (aa)