allopatric speciation
formation of a new species due to reduced gene flow in the presence of a geographic barrier
biological species concept
the idea that a species is defined in terms of their ability to reproduce in nature to form healthy, fertile offspring
chromosome
a structure that contains DNA, the genetic material that is passed from one generation to the next
ecological species concept
the idea that a species is defined based on its ecological niche, which includes all the biotic and abiotic factors in the environment
ecosystem
all organisms living in one geographic region and all the environmental factors that affect those organisms
external fertilization
when sperm and egg fuse outside of a body in the environment
fossil record
all of the fossilized artifacts taken in the context of their placement within Earth's geological strata
gene flow
a change in the gene pool caused by individuals entering or leaving a population
gene pool
the total set of genes of all individuals in a population
gradualism
a process of speciation that involves the accumulation of small genetic changes over a long period of time
hybrid
an offspring produced when members of two species interbreed
hybrid zone
geographic region where two species overlap and the formation of hybrids occurs
internal fertilization
sperm and egg fuse inside a body
macroevolution
evolutionary change at or above the species level
meiosis
a process in cell division during which the number of chromosomes decreases to half the original number by two divisions of the nucleus, resulting in the production of gametes
microevolution
a change in allele frequencies within a population from one generation to the next
mitosis
the process of cell division that results in two cells that are genetic clones of the parent cell
morphological species concept
the idea that a species is defined and characterized by body shape and structure
mutation
a change in DNA sequence
polyploidy
a condition in which an organism has more than the normal number of copies of a set of chromosomes
population
an interbreeding group of individuals of the same species
postzygotic barrier
a reproductive barrier to the development of a hybrid zygote into a healthy, fertile adult
prezygotic barrier
a reproductive barrier at the time of mating or fertilization that impedes the formation of a hybrid zygote
punctuated equilibrium
pattern in the fossil record in which a species undergoes long periods of no change, which are interrupted by large genetic changes over short periods of time
reproductive isolation
state in which reproductive barriers exist to prevent the formation of healthy, fertile offspring from individuals of two different species
speciation
the process through which a species evolves into two or more new species
species
a group of organisms that can reproduce in nature to form healthy, fertile offspring
sympatric speciation
formation of a new species in the absence of a geographic barrier to prevent gene flow
zygote
a fertilized egg