2.G: Unit 2 Glossary

Unit 2.2

adaptation

a heritable trait that aids the survival and reproduction of an organism in its present environment

adaptive evolution

see: natural selection

anagenesis

a gradual change in an entire population's gene frequency

analogous structures

similar traits between two different species that evolved separately (see: convergent evolution)

artificial selection/human-initiated change

any selective breeding intentionally practiced by humans leading to the evolution of domesticated organisms

assortive mating

an individual’s preference to mate with partners who are phenotypically similar to themselves

biogeography

study of the geographic distribution of living things and the abiotic factors that affect their distribution

biostratigraphy

aligning isolated rocks to fossils of organisms that lived for a short period of time

bottleneck effect

a type of genetic drift where a population's size is drastically diminished, reducing variation in the gene pool

cladeogenesis

a population splitting into two distinct evolutionary branches

cline

gradual changes in a trait across an organism's geographic distribution

convergent evolution

where similar traits evolve independently in species that do not share a common ancestry

cosmopolitan species

species that live in a wide variety of geographic areas

directional selection

when, in natural selection, a single phenotype is favored, causing the population to shift towards one end of the trait variation

divergent evolution

species that evolve in diverse directions from a common point (often leading to speciation)

diversifying selection

when, in natural selection, the average is selected against, leading to selection for the rarer variations of a trait

endemic species

species naturally found only in a specific geographic area that is usually restricted in size

evolution

a change in the gene pool of a species over time

evolutionary fitness

the genetic contribution of an individual to future generations

fossil

preserved remains or traces of animals, plants, and other organisms from the past

fossil record

totality of fossils, both discovered and undiscovered, and their placement in rock layers

founder effect

a type of genetic drift where some portion of the population leaves to start a new population in a new location or if a population gets divided by a physical barrier of some kind

gene flow

the flow of alleles in and out of a population due to the migration of individuals or gametes

genetic diversity

variation within a population arising from two main mechanisms: mutation and sexual reproduction

genetic drift

the effect of chance on a population's genetic variation

genetic variation

measure of the genetic differences (diversity of alleles and genotypes) that exist within a population

genetics

study of the mechanisms of inheritance

genotype

genetic makeup of an individual

good genes hypothesis

the selection for harmful traits in sexual selection signals other abilities such as predator avoidance or superior feeding abilities

handicap principle

a type of sexual selection for that selects for harmful traits to maximize reproductive success

homologous structures

traits in two different species derived from a common ancestor

homology

relationship between structures or DNA derived from the most recent common ancestor

hypothesis

a tentative explanation for something that is proposed to either be supported or disproved

intersexual selection

when the more-limited sex chooses their mates from the less-limited sex

intrasexual selection

when those of the less-limited sex compete amongst each other for opportunities to mate with the more-limited sex

macroevolution

processes that gave rise to new species and higher taxonomic groups with widely divergent characters

microevolution

gradual change of a population over time

modern synthesis

the current, coherent understanding of the relationship between natural selection and genetics

molecular clock

the assumed constant rate of DNA mutations over time

mutation

a change in a DNA sequence

natural selection

the more prolific reproduction of individuals with favorable traits that survive environmental change because of those traits

negative frequency-dependent selection

in natural selection, increases the population’s genetic variance by selecting for rare phenotypes

perimineralization

a process of fossilization that occurs when an organism is buried

phenotype

physical, metabolic, or behavioral expression of a genotype

polymorphic

populations with two or more variations of a particular phenotype

population variation

distribution of phenotypes among individuals within a population

positive frequency-dependent selection

in natural selection, decreases the population’s genetic variance by selecting for common phenotypes

radiocarbon dating

method for identifying the age of rocks or fossils less than 60,000 years old, usually based on a comparison between the observed abundance of carbon-14 and its decay products

relative fitness

the proportional genetic contribution of an individual to future generations as compared to others in the population

sexual dimophism

the variation between sexes in a given species due to sexual selection pressures

sexual selection

the selection pressure on males and females to maximize mating success

stabilizing selection

when, in natural selection, the average of a trait is selected for and becomes more common over time, with less variation in the population

stratigraphy

science of understanding the strata, or layers, that form the sedimentary record

theory

a concept that has been extensively tested and supported over time

trace fossil

marks left behind by an organism while it was alive, such as footprints or feces

vestigial structures

structures with no apparent function which appear to be residual parts from a past ancestor

Unit 2.3

adaptive radiation

multiple speciation events originating from a single species

allopatric speciation

geographic separation of populations from a parent species and subsequent evolution into new species

aneuploidy

gametes with too few or two many chromosomes after meiosis

behavioral isolation

prezygotic barrier based on presence or absence of appropriate reproductive behaviors

gametic barrier

prezygotic barrier where gametes are unable to fuse

gene pool

a collection of all the variants of genes in the species

gradual speciation

a model of speciation where species diverge gradually over time in small steps

habitat isolation

prezygotic barrier based on geographic difference in population locations

hybrid inviability

postzygotic barrier where hybrid offspring of two populations do not form normally and/or do not survive past the embryonic stage

hybrid sterility

postzygotic barrier where hybrid offspring are born sterile and unable to reproduce

hybrid zone

an area where two closely-related species continue to interact and reproduce

mechanical barrier

prezygotic barrier where populations are not physically able to mate with one another due to anatomical differences

polyploidy

gametes with extra set, or sets, of chromosomes

postzygotic barrier

type of reproductive isolation that occurs after zygote formation

prezygotic barrier

type of reproductive isolation that blocks reproduction from taking place

punctuated equilibrium

a model of speciation where new species evolve quickly from parent species and then remain largely unchanged for long periods of time

reinforcement

a process of natural selection working to favor individuals that avoid interspecific matings

reproductive isolation

the inability of two populations to interbreed with one another

speciation

a process where a single species branches to form two or more new species

species (biological)

a group of individuals that, in nature, are able to mate and produce viable, fertile offspring

subspecies

geographically separate populations of organisms in the process of allopatric speciation but still able to interbreed

sympatric speciation

speciation due to mutation occurring within a parent species remaining in one location

temporal islation

prezygotic barrier based on differences in timing of mating

zygote

a fertilized egg

Unit 2.4

allele

variations of a gene for a given trait

allele frequency

the rate at which a specific allele exists within a population

genome

the total genetic information of a cell or organism

Hardy-Weinberg Principle

the concept that allele frequencies and genotype ratios in a randomly-breeding population remain constant from generation to generation, given certain criteria

population

a group of individuals that can all interbreed, often distinguished as a species.

population genetics

study of the distributions and changes of allele frequency in a population