AP Bio Unit 7 - Natural Selection and Evolution

Species

A group of similar organisms that can breed and produce fertile offspring.

Population

A group of individuals that belong to the same species and live in the same area

Community

A group of interdependent organisms inhabiting the same region and interacting with each other

Natural selection

The principle that, among the range of inherited trait variations, those contributing to reproduction and survival will most likely be passed on to succeeding generations

Evolution

Change in the genetic characteristics of a population from generation to generation

Adaptation

A trait that helps an organism survive and reproduce

Fitness

Ability of an organism to survive and reproduce in its environment

Overproduction

Organisms produce more offspring than can survive

Variation

Any difference between individuals of the same species.

Sexual reproduction

A reproductive process that involves two parents that combine their genetic material to produce a new organism, which differs from both parents

Competition

the struggle between organisms to survive in a habitat with limited resources

Mutation

A change in the DNA sequence of a gene

Artificial selection

Breeding organisms with specific traits in order to produce offspring with identical traits.

Homologous structures

Structures in different species that are similar because of common ancestry.

Analogous structures

Body parts that share a common function, but not structure

Divergent evolution

when two or more species sharing a common ancestor become more different over time

Convergent evolution

Process by which unrelated organisms independently evolve similarities when adapting to similar environments

Coevolution

Process by which two species evolve in response to changes in each other

Punctuated equilibrium

Pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change

Adaptive radiation

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

Allele

Different forms of a gene

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.

Founder effect

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

Bottleneck effect

A change in allele frequency following a dramatic reduction in the size of a population

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

Stabilizing selection

Natural selection that favors intermediate variants by acting against extreme phenotypes

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

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

p + q = 1

Speciation

Formation of new species

Allopatric speciation

The formation of new species in populations that are geographically isolated from one another.

Sympatric speciation

The formation of new species in populations that live in the same geographic area

Prezygotic barriers

Barriers that impede mating or hinder fertilization.

Postzygotic barriers

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

Hybrid sterility

Hybrid offspring from two different species that fail to produce functional gametes and therefore cannot reproduce (for example: mules)

Structural Isolation

Organisms are unable to reproduce due to differences in their genital organs.

Gametic isolation

A prezygotic reproductive barrier where the sperm of one species may not be able to fertilize the eggs of another species

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.

Cladogram

Diagram that shows the evolutionary relationships among a group of organisms

Phylogenetic tree

A family tree that shows the evolutionary relationships thought to exist among groups of organisms

Most recent common ancestor

The ancestral organism from which a group of descendants arose

Outgroup

An outgroup is a lineage that falls outside the clade being studied but is closely related to that clade.

Taxonomy

The scientific study of how living things are classified

Clade

A group of species that includes an ancestral species and all its descendants.

Three domains of life

Bacteria, Archaea, Eukarya