Chapters 18-20 Evolution

adaptive radiation

when many species evolve from a common ancestor in a relatively short timeframe

allopatric speciation

speciation that occurs via geographic separation

allopolyploid

polyploidy formed between two related, but separate species

autopolyploid

polyploidy formed within a single species

convergent evolution

process by which groups of organisms independently evolve to similar forms

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

habitat isolation

reproductive isolation resulting when species' populations move or are moved to a new

habitat, taking up residence in a place that no longer overlaps with the same species' other populations

homology

phenotypic and/or genetic similarity due to common ancestry

hybrid zone

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

postzygotic barrier

reproductive isolation mechanism that occurs after zygote formation

prezygotic barrier

reproductive isolation mechanism that occurs before zygote formation

sympatric speciation

speciation that occurs in the same geographic space

reinforcement

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

vicariance

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

adaptive evolution

increase in frequency of beneficial alleles and decrease in deleterious alleles due to selection

allele frequency

rate at which a specific allele appears within a population

bottleneck effect

magnification of genetic drift as a result of natural events or catastrophes

cline

gradual geographic variation across an ecological gradient

evolutionary fitness

individual's ability to survive and reproduce

founder effect

a small population becomes isolated from a larger one, resulting in increased genetic drift (and decreased genetic variation) in the new colony

gene flow

exchange of alleles between populations (i.e., by interbreeding)

genetic drift

effect of chance on a population's gene pool

good genes hypothesis

theory of sexual selection that argues individuals develop impressive ornaments to show off their efficient metabolism or ability to fight disease

handicap principle

theory of sexual selection that argues only the fittest individuals can afford costly traits

inbreeding depression

increase in abnormalities and disease in inbreeding populations

macroevolution

broader scale evolutionary changes that scientists see over paleontological time

microevolution

changes in a population's genetic structure

analogy

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

branch point

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

cladistics

system to organize homologous traits to describe phylogenies

class

division of phylum in the taxonomic classification system

molecular systematics

technique using molecular evidence to identify phylogenetic relationships

phylogeny

evolutionary history and relationship of an organism or group of organisms

polytomy

an unresolved set of relationships in a phylogenetic tree

shared ancestral character

describes a characteristic on a phylogenetic tree that all organisms on the tree share

shared derived character

describes a characteristic on a phylogenetic tree that only a certain clade of organisms share

genetic variation

Differences among individuals in the composition of their genes or other DNA segments

phenotypic variation

the variability in phenotypes that exists in a population

species

a group of populations of organisms that are similar in physical appearance and can interbreed to produce viable offspring

biological species concept

defines a species by the ability of two populations to interbreed and produce fit offspring

morphological species concept

defines a species by its phenotypic features