Ap Biology Unit 7

Evolution

Evolution

The change in heritable characteristics of biological populations over successive generations

Adaptations

Physical or behavioral characteristics that have developed to allow an organism to better survive in its environment

Natural selection

The mechanism that drives evolution, where organisms with favorable traits are more likely to survive and reproduce

Homology

Similarity in characteristics due to shared ancestry

Homologous structures

Structures that have the same evolutionary origin but may serve different functions

Vestigial structures

Remnant structures that have lost their original function through evolution

Convergent evolution

The independent evolution of similar features in species of different lineages

Analogous

Structures that have similar functions but different evolutionary origins

Biogeography

The study of the distribution of species and ecosystems in geographic space and through geological time

Microevolution

The change in allele frequencies that occurs over time within a population

Genetic variation

The differences in DNA sequences between individuals of a species

Neutral variation

Multiple alleles present at a given genetic locus that are not distinguishable by natural selection

Population

A group of organisms of the same species living in a particular geographic area

Gene pool

The complete set of unique alleles in a species or population

Hardy-Weinberg equilibrium

A principle stating that allele and genotype frequencies in a population will remain constant in the absence of evolutionary influences

Genetic drift

Random changes in allele frequencies within a population

Founder effect

Loss of genetic variation when a new population is established by a small number of individuals from a larger population

Bottleneck effect

Reduction in genetic diversity due to a sharp decrease in population size

Gene flow

The transfer of genetic material between populations

Adaptive evolution

The process by which organisms become better suited to their environment through natural selection

Relative fitness

The contribution of a genotype to the next generation relative to the contributions of other genotypes

Directional selection

Selection favoring extreme values of a trait

Disruptive selection

Selection favoring extreme values at both ends of a trait distribution

Stabilizing selection

Selection favoring intermediate values of a trait

Heterozygote advantage

When heterozygous individuals have a higher fitness than homozygous individuals

Sexual selection

Selection based on the ability to attract mates

Sexual dimorphism

Distinct differences in appearance between males and females of a species

Phylogeny

The evolutionary history and relationships among species or groups of species

Taxonomy

The science of naming, describing, and classifying organisms

Binomial

The two-part scientific name of a species, consisting of genus and specific epithet

Levels of Linnaean Classification

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

Taxon

A group of organisms classified as a unit

Phylogenetic tree

A branching diagram showing evolutionary relationships among organisms

Branch points

Points on a phylogenetic tree where lineages diverge

Sister taxa

The closest relatives in a phylogenetic tree

Rooted

A phylogenetic tree with a specified common ancestor

Polytomy

A branch point on a phylogenetic tree with more than two immediate descendants

Analogy

Similarity in function but not in evolutionary origin

Shared characters

Traits shared by different species due to common ancestry

Maximum parsimony

A method for inferring phylogenies that minimizes the number of evolutionary changes

Macroevolution

Large-scale evolutionary changes, often leading to new taxonomic groups

Biological species concept

Definition of a species as a group of interbreeding populations reproductively isolated from other such groups

Reproductive isolation

Mechanisms that prevent members of different species from producing viable, fertile offspring

Prezygotic barriers

Reproductive isolating mechanisms that act before fertilization

• temporal, habitat, behavioral, gametic, and mechanical

Postzygotic barriers

Reproductive isolating mechanisms that act after fertilization

• hybrid inviability, hybrid sterility, and hybrid breakdown

Allopatric speciation

Speciation occurring when populations are geographically isolated

Sympatric speciation

Speciation occurring within the same geographic area