Biology 9 Ch. 13 + 14 Vocab

natural selection

a process by which individuals with certain inherited traits are more likely to survive and reproduce than are individuals that do not have those traits

adaptation

an inherited character that enhances an organism's ability to survive and reproduce in a particular environment

theory

a widely accepted explanatory idea that is broader in scope than a hypothesis, generates new hypotheses, and is supported by a large body of evidence

evolution

descent with modification; the idea that living species are descendants of ancestral species that were different from present-day ones

fossil

a preserved remnant or impression of an organism

stratum (pl. strata)

rock layers formed when a new layer of sediment covers an older one and compresses it

paleontologist

a scientist who studies fossils

fossil record

the chronicle of evolution over millions of years of geologic time engraved in the order in which fossils appear in rock strata

homology

similarity in characters resulting from a shared ancestry

homologous structures

features in different species that often have different functions but are structurally similar because of common ancestry

molecular biology

the study of biological structures, functions, and heredity at the molecular level

vestigial structure

a feature of an organism that is a historical remnant of a structure that served a function in the organism's ancestors

evolutionary tree

a branching diagram that reflects a hypothesis about evolutionary relationships among groups of organisms

artificial selection

the selective breeding of domesticated plants and animals to promote the occurrence of desirable traits in the offspring

mutation

a change in the genetic information of a cell; the ultimate source of genetic diversity; change in genetic information encoded in the nucleotide sequence of DNA

population

a group of individuals belonging to one species and living in the same geographic area; the individuals can potentially interbreed

gene pool

all copies of every type of allele at every locus in all members of a population

microevolution

a change in a population's gene pool over generations

Hardy-Weinberg equilibrium

the state of a population in which frequencies of alleles and genotypes in a population remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work

genetic drift

a change in the gene pool of a population due to chance; effects are most pronounced in small populations

bottleneck effect

genetic drift resulting from a drastic reduction in population size; typically, the surviving population is not longer genetically representative of the original 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 is not reflective of that of the original population

gene flow

the transfer of alleles from one population to another as a result of the movement of individuals or their gametes

relative fitness

the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals in the population

directional selection

natural selection in which individuals at one end of the phenotypic range survive and reproduce more successfully than do other individuals

stabilizing selection

natural selection that favors intermediate variants by acting against extreme phenotypes

disruptive selection

natural selection in which individuals on both extremes of a phenotypic range are favored over intermediate phenotypes

sexual selection

a form of natural selection in which individuals with certain inherited traits are more likely than other individuals to obtain mates

sexual dimorphism

marked differences between the secondary sex characteristics of males and females

balancing selection

natural selection that maintains stable frequencies of two or more phenotypic forms in a population

heterozygote advantage

greater reproductive success of heterozygous individuals compared with homozygotes; tends to preserve variation in gene pools

speciation

the evolution of a new species; process by which one species splits into two or more species

biological species concept

definition of a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but do not produce viable, fertile offspring with members of other such groups

species

a group of populations whose members have the potential to interbreed and produce viable, fertile offspring

reproductive isolation

the existence of biological factors (barriers) that impede members of two species from producing viable, fertile offspring

hybrid

offspring that results from the mating of individuals from two different species

morphological species concept

a definition of species in terms of measurable anatomical criteria

ecological species concept

a definition of species in terms of ecological niche, the sum of how members of the species interact with the nonliving and living parts of their environment

phylogenetic species concept

a definition of species as the smallest group of individuals that shares a common ancestor, forming one branch on the tree of life

prezygotic barriers

a reproductive barrier that impedes mating between species or hinders fertilization if mating between two species is attempted; includes temporal, habitat, behavioral, mechanical, and gametic isolation

postzygotic barriers

a reproductive barrier that prevents hybrid zygotes produced by two different species from developing into viable, fertile adults; includes hybrid viability, reduced hybrid fertility, and hybrid breakdown

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

polyploid

an organism that has more than two complete sets of chromosomes as a result of an accident in cell division

adaptive radiation

period of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill new or vacant ecological roles in their communities

hybrid zone

a geographic region in which members of different species meet and mate, producing at least some hybrid offspring

punctuated equilibria

in the fossil record, long periods in which a species undergoes little or no morphological change, interrupted by relatively brief periods of sudden change