AP Biology - Unit 7

Directional Selection - When one end of the range of phenotypes is favored by natural selection.

Sexual Selection - When individuals with certain characteristics are more likely to attract mates than other individuals. 

Selective Pressure - Any biotic or abiotic factors influencing survivability.

Artificial Selection - The process by which humans breed other animals and plants for particular traits. 

Convergent Evolution - Species that live in similar environments may evolve similar adaptations even though they may not have a recent common ancestor. 

Analogous Structure - Features of different species that are similar in function, but not necessarily in structure.

Genetic Drift - The random change in the frequency of a particular allele within a population.

Founder Effect - A random process that reduces genetic variation within a small population due to separation from a larger population. 

Gene Flow - The movement of individuals between populations causing an exchange of alleles between populations.

Bottleneck Effect - Genetic drift resulting from the reduction of a population.

Homologous Structures - Variation in a structure that was present in a common ancestor (same structure, different function).

Vestigal Structures - Reduced or obsolete features that serve little or no purpose for the organism.

Speciation - Occurs when two populations become reproductively isolated from one another.

Adaptive Radiation - Refers to the evolution of new species that allows empty ecological roles or niches to be filled. 

Phyletic Gradualism - Evolution occurs by the gradual accumulation of small changes.

Punctuated Equilibrium - A long period of stability in a species interrupted by periods of rapid evolution.

Allopatric Speciation - A larger population becomes geographically separated and the smaller subgroups diverge and become separate species over time. 

Sympatric Speciation - Refers to the evolution of a new species due to individuals being reproductively isolated from a surviving ancestral population. 

Prezygotic Barriers - Prevent the formation of a zygote, or a fertilized egg.

Postzygotic Barriers - Occurs after the zygote is formed, and they prevent the zygote from developing into a viable and fertile adult organism.

Habitat Isolation - If organisms live in different habitats and do not come in contact with one another, they cannot mate and form zygotes and are thus reproductively isolated.

Temporal Isolation - Organisms can live in the same habitat, but if they are active at different times of the day or have breeding seasons during different times of the year, they will be temporally isolated and will not interbreed.

Behavioral Isolation - Some species will interbreed only with others who perform compatible mating behaviors, such as mating calls or dances. 

Mechanical Isolation - If the sexual organs of the organisms are incompatible and prevent the transfer of gametes, the species will remain reproductively isolated. 

Gametic Isolation - Even if two organisms are able to successfully copulate, if their gamates are incomparible, no zygote will be produced and the organisms will be reproductively isolated.