Exam 1: Chapter 18: Key Terms: Evolution and Natural Selection

adaptation

heritable trait or behavior in an organism that aids in its survival and reproduction in its present environment

adaptive radiation

speciation when one species radiates to form several other species

allopatric speciation

speciation that occurs via geographic separation

polyploid

individual with an incorrect number of chromosome sets

allopolyploid

polyploidy formed between two related, but separate species

aneuploidy

condition of a cell having an extra chromosome or missing a chromosome for its species

autopolyploid

polyploidy formed within a single species

behavioral isolation

type of reproductive isolation that occurs when a specific behavior or lack of one prevents reproduction from taking place

convergent evolution

process by which groups of organisms independently evolve to similar forms

dispersal

allopatric speciation that occurs when a few members of a species move to a new geographical area

divergent evolution

process by which groups of organisms evolve in diverse directions from a common point

gametic barrier

prezygotic barrier occurring when closely related individuals of different species mate, but differences in their gamete cells (eggs and sperm) prevent fertilization from taking place

gradual speciation model

model that shows how species diverge gradually over time in small steps

habitat isolation

reproductive isolation resulting when species' populations move or are moved to a new habitat, taking up residence in a place that no longer overlaps with the same species' other populations

homologous structures

parallel structures in diverse organisms that have a common ancestor

hybrid

offspring of two closely related individuals, not of the same species

hybrid zone

area where two closely related species continue to interact and reproduce, forming hybrids

natural selection

reproduction of individuals with favorable genetic traits that survive environmental change because of those traits, leading to evolutionary change

postzygotic barrier

reproductive isolation mechanism that occurs after zygote formation

prezygotic barrier

reproductive isolation mechanism that occurs before zygote formation

punctuated equilibrium

model for rapid speciation that can occur when an event causes a small portion of a population to be cut off from the rest of the population

reinforcement

continued speciation divergence between two related species due to low fitness of hybrids between them

reproductive isolation

situation that occurs when a species is reproductively independent from other species; behavior, location, or reproductive barriers may cause this to happen

speciation

formation of a new species

species

group of populations that interbreed and produce fertile offspring

sympatric speciation

speciation that occurs in the same geographic space

temporal isolation

differences in breeding schedules that can act as a form of prezygotic barrier leading to reproductive isolation

variation

genetic differences among individuals in a population

vestigial structure

physical structure present in an organism but that has no apparent function and appears to be from a functional structure in a distant ancestor

vicariance

allopatric speciation that occurs when something in the environment separates organisms of the same species into separate groups