Genetics, Evolution, and Speciation: Key Concepts and Definitions

mutation

a random error in gene replication that leads to a change

genetic drift

random change in allele frequencies that occurs in small populations

bottleneck effect

a reduction in the genetic diversity of a population caused by a reduction in its size

founder effect

change in allele frequencies as a result of the migration of a small subgroup of a population

polymorphism

The coexistence of two or more distinct forms in the same population.

continuous variation

variation in a population showing an unbroken range of phenotypes rather than discrete categories

heterozygosity

having different alleles at a gene locus

fitness

Ability of an organism to survive and reproduce in its environment

diploidy

maintains genetic variation in the form of hidden recessive alleles

intrasexual selection

competition among males

intersexual selection

Selection whereby individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex; also called mate choice.

microevolution

Change in allele frequencies in a population over generations.

macroevolution

large-scale evolutionary changes that take place over long periods of time

Anagenisis

species formation without branching of the evolutionary line of descent.

Cladogensis

is branching speciation, where one species diversifies and becomes two or more new species

prezygotic barriers

Barriers that impede mating or hinder fertilization.

postzygotic barriers

Barriers that prevent the hybrid zygote from becoming a fertile adult.

allopatric

The formation of a new species as a result of an ancestral population's becoming isolated by a geographic barrier.

sympatric

The formation of a new species as a result of a genetic change that produces a reproductive barrier between the changed population (mutants) and the parent population. No geographic barrier is present.

autopolyploidy

an individual that has more than two chromosome sets that are all derived from a single species

allopolyploidy

polyploidy resulting from contribution of chromosomes from two or more species

exaptation

shaping of a useful feature of an organism by natural selection to perform one function and the later reshaping of it by different selection pressures to perform a new function

heterochrony

Evolutionary change in the timing or rate of an organism's development.

homeotic genes

Genes that determine basic features of where a body part is.

allele frequencies

Proportion of different alleles in a population.

independent assortment

Independent segregation of genes during the formation of gametes

geographic variation

differences in the genetic composition of separate populations

clinal variation

gradual change in the phenotype of a species over a geographic gradient

directional selection

Form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

disruptive selection

form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

stabilizing selection

Natural selection that favors intermediate variants by acting against extreme phenotypes

biological species concept

Species is a group of populations whose members have the potential to produce fertile offspring.

morphological species concept

characterizes a species by body shape and other structural features

adaptive radiation

An evolutionary pattern in which many species evolve from a single ancestral species

phylogenic species concept

defines a species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life

ecological species concept

A definition of species in terms of ecological niche, the sum of how members of the species interact with the nonliving and living parts of their environment.

paleontological species concept

Definition of species based on morphological differences known only from the fossil record.