Natural Selection
A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.
Adaptation
inherited characteristic that increases an organism's chance of survival
Descent with modification
principle that each living species has descended, with changes, from other species over time
Homology
Similarity in characteristics resulting from a shared ancestry.
Analogy
similarities among unrelated species that result from convergent evolution
Vestigial Structures
remnant of a structure that may have had an important function in a species' ancestors, but has no clear function in the modern species.
Convergent Evolution
Process by which unrelated organisms independently evolve similarities when adapting to similar environments
Divergent Evolution
when two or more species sharing a common ancestor become more different over time
Adaptive Radiation(Divergent Evolution)
An evolutionary pattern in which many species evolve from a single ancestral species
Biogeography
Study of past and present distribution of organisms
Endemic Species
species that are native to and found only within a limited area
Phylogeny
Evolutionary history of a species or group of species.
Genus
group of closely related species; the first part of the scientific name in binomial nomenclature
Microevolution
Evolutionary change below the species level; change in the allele frequencies in a population over generations.
Macroevolution
large-scale evolutionary changes that take place over long periods of time
Species
A group of similar organisms that can breed and produce fertile offspring.
Speciation
the formation of new and distinct species in the course of evolution.
Reproductive Isolation
Separation of species or populations so that they cannot interbreed and produce fertile offspring
Prezygotic Barriers
A reproductive barrier that impedes mating between species or hinders fertilization if interspecific mating is attempted
Habitat Isolation
Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers
Temporal Isolation
form of reproductive isolation in which two populations reproduce at different times
Behavioral Isolation
isolation between populations due to differences in courtship or mating behavior
Mechanical Isolation
mating is attempted, but morphological differences prevent its successful completion
Gametic Isolation
Sperm of one species may not be able to fertilize eggs of another species
Postzygotic Barriers
Barriers that prevent the hybrid zygote from becoming a fertile adult.
Allopatric Speciation
The formation of a new species as a result of an ancestral population's becoming isolated by a geographic barrier.
Sympatric Speciation
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.
Genetic Variation
Differences among individuals in the composition of their genes or other DNA segments
Population
A group of individuals that belong to the same species and live in the same area
Gene Pool
All the genes, including all the different alleles for each gene, that are present in a population at any one time
Genetic Drift
A change in the allele frequency of a population as a result of chance events rather than natural selection.
Bottleneck Effect
A change in allele frequency following a dramatic reduction in the size of a population
Founder Effect
Genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population.
Gene Flow
Movement of alleles into or out of a population due to the migration of individuals to or from the population
Fitness
how well an organism can survive and reproduce in its environment
Stabilizing Selection
Natural selection that favors intermediate variants by acting against extreme phenotypes
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
natural selection in which individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle of the curve
Sexual Selection
A form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates.
Artificial Selection
Selection by humans for breeding of useful traits from the natural variation among different organisms
Extinction
A term that typically describes a species that no longer has any known living individuals.
Punctuated Equilibrium
Pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change
Phylogenetic Tree
A family tree that shows the evolutionary relationships thought to exist among groups of organisms
Gradualism
The theory that evolution occurs slowly but steadily
Alleles
Different forms of a gene
Hardy-Weinberg Equilibrium
condition that occurs when the frequency of alleles in a particular gene pool remain constant over time
Conditions for Hardy-Weinberg Equilibrium
1. No mutations
2. Random mating
3. No natural
selection
4. Extremely large population size
5. No gene flow
Hardy-Weinberg Equation
p^2 + 2pq + q^2 = 1, where p is the frequency of the dominant allele and q is the frequency of the recessive allele. It predicts the frequency of homozygous dominants, homozygous recessives, and heterozygotes.
p
frequency of dominant allele
q
frequency of recessive allele
p^2
frequency of homozygous dominant genotype
2pq
frequency of heterozygous genotype
q^2
frequency of homozygous recessive genotype