Chapter 21 - Evolutionary Populations and the Hardy-Weinberg Principle

Law of Segregation

During meosis, each egg/sperm get one randomly selected allele

What are the four agents of evolutionary change?

1. Mutation
2. Genetic Drift
3. Migration
4. Natural Selection

Random Genetic Drift

Random changes in allele frequency in a population

Where is genetic drift the strongest?

In small populations

What effect does random genetic drift have because of loss of alleles?

Reduced genetic variation in the population

Founder Effect

Small number of individuals start a new population, with a random allele selection.

Population Bottleneck

Rapid environmental change (chance event or catastrophe) causes extreme reduction in the size of the population

Migration

Gene flow, movement of individuals or gametes, tends to reduce genetic differences between populations

Directional Selection

Individuals of one extreme phenotype favored

Disruptive Selection

Both extreme phenotypes favored; intermediate types selected against

Stabilizing Selection

Individuals with intermediate phenotype favored; extreme phenotypes selected against

Balancing Selection

Natural selection maintains stable frequencies of two or more phenotypic forms in a population

Heterozygote Advantage

Heterozygotes have a higher fitness than homozygotes

Sexual Selection

Occurs when certain traits make you more likely to obtain a mate

Sexual Dimorphism

Phenotypic differences between sexes

Intrasexual Selection

Competition within the same sex (males); sperm competition