Miller and Levine Biology Chapter 17

Gene Pool
Consists of all genes, including all the different alleles for each gene, that are present in a population.
Allele Frequency
The number of times an allele occurs in a gene pool, compared to the total number of alleles in that pool for the same gene.
Single-gene Trait
A trait controlled by only one gene.
Polygenic Traits
Many traits are controlled by two or more genes; each gene usually has two or more alleles.
Directional Selection
When individuals at one end of the curve have higher fitness than individuals in the middle or at the other end.
Stabilizing Selection
When individuals near the center of the curve have higher fitness than individuals at either end.
Disruptive Selection
When individuals at the outer ends of the curve have higher fitness than individuals near the middle of the curve.
Genetic Drift
Random change in allele frequency caused by a series of chance occurrences that cause an allele to become more or less common in a population.
Bottleneck Effect
A change in allele frequency following a dramatic reduction in size of a population.
Founder Effect
Allele frequencies change as a result of the migration of a small subgroup of a population.
Genetic Equilibrium
If a population is not evolving, allele frequencies in its gene pool do not change.
Hardy-Weinberg Principle
Allele frequencies in a population should remain constant unless one or more factors cause those frequencies to change.
Sexual Selection
Individuals select mates based on heritable traits, such as size, strength, or coloration.
A population or group of populations whose members can interbreed and produce fertile offspring.
The formation of a new species.
Reproductive Isolation
When two populations no longer interbreed.
Behavioral Isolation
Form of reproductive isolation in which two populations develop differences in courtship rituals or other behaviors that prevent them from breeding.
Geographic Isolation
When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water.
Temporal Isolation
When two or more species reproduce at different times.
Molecular Clock
Uses mutation rates in DNA to estimate the time that two species have been evolving independently.
A species which has died out.