Hardy-Weinberg & Agents of Evolution

What does the Hardy-Weinberg Principle state about allele and genotype frequencies?

They will remain constant from generation to generation, indicating an absence of evolutionary change.

What is the HWE used for in population genetics?

 It acts as a null model to determine what the genetic makeup of a population would be if it were not evolving at a particular gene locus.

State the two Hardy-Weinberg equations and what they represent.

Allele frequencies: \mathbf{p + q = 1} (where p and q are the frequencies of the two alleles). Genotype frequencies: \mathbf{p^2 + 2pq + q^2 = 1}.

What does the term 2pq represent in the HWE equation?

The predicted frequency of the heterozygous genotype (e.g., C^R C^W).

List the five conditions required for a population to be in Hardy-Weinberg Equilibrium (i.e., no evolution).

1. No Mutations. 2. No Gene Flow (closed population). 3. Infinite Population Size (very large). 4. No Natural Selection (equal survival/reproduction). 5. Random Mating with respect to genotype.

In the Snapdragon example (p=0.7, q=0.3), the predicted C^W C^W frequency was 0.09 (9%), but the observed frequency was 0.167 (16.7%). What does this indicate?

The population is evolving (it is NOT in HWE). Specifically, there is selection for the C^W allele (or selection against the C^R allele).

What are the five agents of microevolutionary change?

1. Mutation 2. Gene Flow 3. Genetic Drift 4. Nonrandom Mating 5. Natural Selection.

Define Mutation and state its effect on genetic variation.

A spontaneous heritable change in DNA. It is the major source of heritable variation and introduces new genetic variation into a population.

What is Gene Flow (aka Migration) and how does it affect populations?

The movement of alleles across different populations (e.g., movement of individuals or gametes like pollen). It may introduce genetic variation from another population.

Define Genetic Drift and what makes a population vulnerable to it?

Random change in allele frequencies caused by chance events. It is most important in smaller populations and reduces genetic variability.

Differentiate the two types of Genetic Drift.

Population Bottleneck: A reduction in alleles due to a drastic, temporary reduction in population size (e.g., disaster).

Founder Effect: A reduction in alleles due to a few individuals starting a new population.

What is Nonrandom Mating and its effect on allele frequencies and HWE?

The choice of mates based on their phenotypes and genotypes. It does not directly affect allele frequencies, but usually prevents genetic equilibrium (HWE).

Define Natural Selection.

Differential survivorship or reproduction of individuals with different genotypes. Individuals with certain traits survive and reproduce at higher rates than others.

How is Natural Selection measured?

Through Relative Fitness, which is the contribution an individual makes to the gene pool of the next generation, relative to the contribution of others.

Which type of selection favors individuals at one end of the phenotypic spectrum?

Directional Selection.

Which type of selection favors individuals with intermediate phenotypes?

Stabilizing Selection.

Which type of selection favors individuals with extreme phenotypes?

Disruptive Selection.