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34 terms

Honors Biology Ch. 18

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Population
Group of individuals of the same species in a specified area
Gene Pool
Pool of genetic resources
Alleles
Different forms of genes in a gene pool (in a sexually reproducing population)
Lethal Mutation
Mutation that drastically changes phenotype, usually results in death
Neutral Mutation
Mutation that changes the base sequence of DNA, but the alteration has no effect on survival or reproduction--neither helps nor hurts the individual
Allele Frequencies
The relative abundances of alleles of a given gene among all individuals of a population, starting from a theoretical reference point
Genetic Equilibrium
A theoretical reference point which occurs when a population is not evolving with respect to the gene
Microevolution
Of a population or species, small-scale change in allele frequencies. Occurs by mutation, natural selection, genetic drift, gene flow
Natural Selection
Differential survival and reproduction among individuals of a population that vary in the details of their shared traits. Influences the frequency of alleles in a population by operating on phenotypes that have a genetic basis.
Directional Selection
Allele frequencies shift in a consistent direction, so forms at one end of a range of phenotypic variation become more common over time.
Stabilizing Selection
An intermediate form of a trait is favored, and extreme forms are not
Disruptive Selection
Forms of a trait at both ends of a range of variation are favored, and intermediate forms are selected against
Sexual Dimorphism
Having distinct male and female phenotypes
Sexual Selection
Mode of natural selection in which some individuals, the genetic winners, out-reproduce others of a population because they are better at securing mates. Most adaptive forms of a trait are those that help individuals defeat same-sex rivals for mates, or are the ones most attractive to the opposite sex.
Balanced Polymorphism
The maintenance of two or more alleles for a trait in some populations, as a result of natural selection against homozygotes
Genetic Drift
Random change in allele frequencies over time, brought about by chance alone
Fixation
This happens when all individuals of a population are homozygous for one allele
Bottleneck
A drastic reduction in population size brought about by severe pressure
Founder Effect
A form of bottlenecking. Change in allele frequencies that occurs after a few individuals establish a new population
Inbreeding
Breeding or mating between close relatives, which share a large number of alleles
Gene Flow
The movement of alleles among populations
Reproductive Isolation
Any mechanism that prevents gene flow between populations. Part of speciation
Speciation
Formation of daughter species from a population or subpopulation of a parent species; the routes vary in their details and duration
Allopatric Speciation
A speciation mode by which a physical barrier separates two population and ends the gene flow between them. Then reproductive isolation mechanisms arise
Sympatric Speciation
A speciation mode by which new species form within the home range of an existing species, in the absence of a physical barrier
Parapatric Speication
A speciation mode in which different selection pressures lead to divergences within a single population. May occur when one population extends across a broad region encompassing diverse habitats
Macroevolution
Evolutionary patterns on a larger scale
Covevolution
The process by which close ecological interatctions between two species cause them to evolve jointly
Stasis
A lineage persists for millions of years with little or no change
Exaptation
Adaptation of an existing structure for a completely diffferent purpose; a major evolutionary novelty
Adaptive Radiation
A burst of divergences from a single lineage
Key Innovation
A structural or functional modification that bestows upon its bearer the opportunity to exploit a habitat more efficiently or in a novel way
Extinct
Irrevocably lost from the Earth
Mass Extinctions
Losses of many lineages