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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