BIO 2 Chapters 22-24

frequency dependent selection

selection in which the fitness of a phenotype depends on how common the phenotype is in a population

macroevolution

evolutionary change above the species level

bottleneck effect

genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions

hybrid

offspring that results from the mating of individuals from two different species or from two true breeding varieties of the same species

Hardy-Weinberg equilibrium

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

genetic drift

process in which chance events cause unpredictable fluctuations in allele frequencies from one generation to the next

adaptation

inherited characteristics of an organism that enhances its survival and reproduction in a specific environment.

neutral variation

genetic variation that does not provide a selective advantage or disadvantage

evolutionary tree

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

punctuated equilibria

long periods of apparent stasis, in which a species undergoes little or no morphological change, interrupted by relatively brief periods of sudden change

stabilizing selection

natural selection in which intermediate phenotypes survive or reproduce more successfully than do extreme phenotypes

genetic variation

differences among individuals in the composition of their genes or other DNA sequences

stratum

rock layer formed when new layers of sediment cover older ones and compress them

relative fitness

contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals in 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 composition is not reflective of that of the original population

balancing selection

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

polyploidy

chromosomal alteration in which the organism possesses more than two complete chromosome sets

gene flow

transfer of alleles from one population to another, resulting from the movement of fertile individuals or their gametes

vestigial structure

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

allopolyploid

fertile individual that has more than two chromosome sets as a result of two different species interbreeding and combining their chromosomes

artificial selection

selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits

homology

similarity in characteristics resulting from shared ancestry

reproductive isolation

existence of biological factors that impede members of two species from producing viable, fertile offspring

biogeography

scientific study of past and present geographic distributions of species

autopolyploid

individual that has more than two chromosome sets that are all derived from a single species

gene pool

aggregate of all copies of every type of allele at all loci in every individual in a population

hybrid zone

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

population

group of individuals of the same species that live in the same area and interbreed, producing fertile offspring

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

morphological species concept

definition of a species in terms of measurable anatomical criteria

reinforcement

process in which natural selection strengthens pre zygotic barriers to reproduction, reducing chances of hybrid formation

intrasexual selection

form of natural selection in which there is direct competition among individuals of one sex for mates of the opposite sex

pre zygotic barrier

reproductive barrier that impedes mating between species or hinders fertilization if interspecific mating is attempted

directional selection

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

allopatric speciation

formation of new species in populations that are geographically isolated from one another

fossil

preserved remnant or impression of an organism that lived in past

disruptive selection

natural selection in which individuals on both extremes of a phenotypic range survive or reproduce more successfully than do individuals with intermediate phenotypes

postzygotic barrier

reproductive barrier that prevents hybrid zygotes produced by two different species from developing into viable, fertile adults

adaptive evolution

process in which traits that enhance survival or reproduction tend to increase in frequency over time, resulting in a b better match between organisms and their environment

microevolution

evolutionary change below the species level

convergent evolution

evolution of similar features in independent evolutionary lineages

intersexual selection

form of natural selection in which individuals of one sex are choosy in selecting their mates from the other sex

species

population or 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

pangaea

supercontinent that formed near the end of the Paleozoic era, when plate movements brought all the landmasses of earth together

sexual selection

process in which individuals with certain inherited characteristics are more likely than other individuals of same sex to obtain mates

evolution

descent with modification, process by which species accumulate differences from their ancestors as they adapt to different environments over time

paleontology

study of fossils

sympatric speciation

formation of new species in populations that live in the same geographic area

natural selection

process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits

heterozygote advantage

greater reproductive success of heterozygous individuals compared with homozygotes

homologous structures

structures in different species that are similar because of common ancestry

analogous

having characteristics that are similar because of convergent evolution, not homology

ecological species concept

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

sexual dimorphism

differences between secondary sex characteristics of males and females of same species

speciation

evolutionary process in which one species splits into two or more species