AP Biology Unit 7: Natural Selection Key Terms

acquired characteristics

modifications caused by an individual's environment that can be inherited by its offspring

adaptation

heritable trait or behavior in an organism that aids in its survival and reproduction in its present environment

adaptive radiation

speciation when one species radiates out to form several other species

allopatric speciation

speciation that occurs via geographic separation

allopolyploid

polyploidy formed between two related, but separate species

Aneuploidy

condition of a cell having an extra chromosome or missing a chromosome for its species

Autopolyploidy

polyploidy formed within a single species

behavioral isolation

type of reproductive isolation that occurs when a specific behavior or lack of one prevents reproduction from taking place

convergent evolution

process by which groups of organisms independently evolve to similar forms

dispersal

allopatric speciation that occurs when a few members of a species move to a new geographical area

divergent evolution

process by which groups of organisms evolve in diverse directions from a common point

gametic barrier

prezygotic barrier occurring when closely related individuals of different species mate, but differences in their gamete cells (eggs and sperm) prevent fertilization from taking place

gradual speciation model

model that shows how species diverge gradually over time in small steps

habitat isolation

reproductive isolation resulting when populations of a species move or are moved to a new habitat, taking up residence in a place that no longer overlaps with the other populations of the same species

homologous structures

parallel structures in diverse organisms that have a common ancestor

hybrid

offspring of two closely related individuals, not of the same species

hybrid zone

area where two closely related species continue to interact and reproduce, forming hybrids

natural selection

reproduction of individuals with favorable genetic traits that survive environmental change because of those traits, leading to evolutionary change

polyploidy

gametes with extra chromosomes

postzygotic barrier

reproduction isolation mechanism that occurs after zygote formation

prezygotic barrier

reproductive isolation mechanism that occurs before zygote formation

punctuated equilibrium

model for rapid speciation that can occur when an event causes a small portion of a population to be cut off from the rest of the population

reinforcement

continued speciation divergence between two related species due to low fitness of hybrids between them

reproductive isolation

situation that occurs when a species is reproductively independent from other species; this may be brought about by behavior, location, or reproductive barriers

speciation

Formation of a new species

species

group of populations that interbreed and produce fertile offspring

sympatric speciation

speciation that occurs in the same geographic space

temporal isolation

differences in breeding schedules that can act as a form of prezygotic barrier leading to reproductive isolation

theory of evolution

explains how populations change over time and how life diversifies the origin of species

variation

genetic differences among individuals in a population

vestigial structure

a physical structure present in an organism but that has no apparent function and appears to be from a functional structure in a distant ancestor

vicariance

allopatric speciation that occurs when something in the environment separates organisms of the same species into separate groups

analogy (homoplasy)

characteristic that is similar between organisms by convergent evolution, not due to the same evolutionary path

basal taxon

branch on a phylogenetic tree that has not diverged significantly from the root ancestor

binomial nomenclature

system of two-part scientific names for an organism, which includes genus and species names

branch point

node on a phylogenetic tree where a single lineage splits into distinct new ones

cladistics

system used to organize homologous traits to describe phylogenies

cladograms

visual representations of evolutionary relationships between organisms

class

division of phylum in the taxonomic classification system

eukaryote-first hypothesis

proposal that prokaryotes evolved from eukaryotes

family

division of order in the taxonomic classification system

gene transfer agent (GTA)

bacteriophage-like particle that transfers random genomic segments from one species of prokaryote to another

genome fusion

fusion of two prokaryotic genomes, presumably by endosymbiosis

genus

division of family in the taxonomic classification system; the first part of the binomial scientific name

homology

Similarity in characteristics resulting from a shared ancestry

horizontal gene transfer (HGT)

(also, lateral gene transfer) transfer of genes between unrelated species

kingdom

division of domain in the taxonomic classification system

maximum parsimony

applying the simplest, most obvious way with the least number of steps

mitochondria-first hypothesis

proposal that prokaryotes acquired a mitochondrion first, followed by nuclear development

molecular systematics

technique using molecular evidence to identify phylogenetic relationships

monophyletic group (clade)

organisms that share a single ancestor

nucleus-first hypothesis

proposal that prokaryotes acquired a nucleus first, and then the mitochondrion

order

division of class in the taxonomic classification system

parsimony

the simplest, most straightforward way of constructing phylogenetic and evolutionary relationships between organisms

phylogenetic tree

diagram used to reflect the evolutionary relationships among organisms or groups of organisms

phylogeny

evolutionary history and relationship of an organism or group of organisms

phylum

division of kingdom in the taxonomic classification system

polytomy

branch on a phylogenetic tree with more than two groups or taxa

ring of life

phylogenetic model where all three domains of life evolved from a pool of primitive prokaryotes

rooted

single ancestral lineage on a phylogenetic tree to which all organisms represented in the diagram relate

shared ancestral character

describes a characteristic on a phylogenetic tree that is shared by all organisms on the tree

shared derived character

describes a characteristic on a phylogenetic tree that is shared only by a certain clade of organisms

sister taxa

two lineages that diverged from the same branch point

systematics

field of organizing and classifying organisms based on evolutionary relationships

taxon

a single level in the taxonomic classification system

taxonomic classification system

hierarchical system of classifying organisms, including the classification of domain, kingdom, phylum, class, order, family, genus, and species

taxonomy

science of classifying organisms

web of life

phylogenetic model that attempts to incorporate the effects of horizontal gene transfer on evolution