Variations in Populations - AP Biology

A gradual change in a trait across a geographic range. Results from adaptation to varying environmental conditions.

Temporal isolation. Breeding occurs at different times, preventing mating.

Ability to survive and reproduce in a given environment. Measured by relative reproductive success compared to others.

The presence of two or more variants in a population. Maintained by balancing selection or neutral evolution.

The exchange of genetic material between different organisms. Produces new allele combinations in offspring.

Small population size. Fewer individuals mean greater random sampling effects.

It provides material for natural selection to act upon. Higher variation enables response to environmental challenges.

Loss of genetic diversity. Random changes reduce total genetic variation over time.

A mechanism that reduces the viability or reproductive capacity of hybrids. Acts after fertilization to reduce hybrid success.

The rapid evolution of diversely adapted species from a common ancestor. Often occurs when new habitats become available.

Selection that favors one extreme phenotype. Shifts population mean toward the favored extreme.

A variant form of a gene. Different versions arise through mutation and recombination.

Assortative mating. Individuals mate based on similar traits or characteristics.

Reduction in genetic diversity due to a dramatic population decrease. Survivors carry only a subset of original genetic diversity.

Observable characteristics of an organism. Results from interaction between genotype and environment.

Allele frequencies do not change across generations. Indicates no net evolutionary change is occurring.

Genotype. Determines which proteins are produced by an organism.

Allele and genotype frequencies remain constant in a population at equilibrium. Assumes no evolution is occurring in the population.

It introduces new genetic variations. Without mutations, populations lack raw material for evolution.

Proportion of an allele in a population's gene pool. Changes over time through evolutionary forces.

Random changes in allele frequencies in a population. Stronger in small populations due to sampling effects.

Mutation. Creates new alleles through DNA sequence changes.

Stabilizing selection. Reduces variation by eliminating extreme phenotypes.

Natural selection. Individuals with beneficial traits produce more offspring.

Reproductive isolation. Prevents gene flow between diverging populations.

A sharp reduction in the size of a population. Results in loss of rare alleles through random sampling.

An allele rises in frequency because it is linked to a beneficial allele. Occurs due to linkage disequilibrium between loci.

Rapid evolutionary change followed by periods of stability. Explains patterns seen in fossil records.

Crossing over. Exchanges chromosome segments between homologs during prophase I.