chapter 21 Flashcards
natural selection
the process in which, when there is inherited variation in a population of organisms, the variants best suited for growth and reproduction in a given environment contribute disproportionately to future generations
gene pool
all the alleles present in all individuals in a population or species
population
all the individuals of a given species that live and reproduce in a particular place
deleterious mutation
harmful effect on an organism
neutral mutation
little or no effect on an organism
advantageous mutation
improve their carriers’ chances of survival or reproduction
adaptation (adapted)
in an evolutionary context, the fit between an organism and its environment the results from evolution by natural selection
allele frequency
among all the alleles of a gene in a population, the proportion that are a specified allele
fixation (fixed)
population exhibits only one allele at a particular gene
Hardy-Weinberg equilibrium
describes the situation in which evolution does not occur
genetic drift
a change in the frequency of an allele due to the random effects of limited population size
non-random mating
when individuals do not mate randomly
Modern Synthesis
the current theory of evolution, which combines Darwin’s theory of natural selection and Mendelian genetics
positive selection
natural selection that increases the frequency of a favorable allele
negative selection
natural selection that decreases the frequency of a deleterious allele
balancing selection
natural selection that acts to maintain two or more alleles of a given gene in a population
heterozygote advantage
a form of balancing selection in which the heterozygote’s fitness is higher than that of either of the homozygotes, resulting in selection that ensures that both alleles remain in the population at intermediate frequencies
stabilizing selection
maintains the status quo and acts against extremes
directional selection
leads to a change in a trait over time
disruptive selection
operates in favor of extremes and against intermediate forms
artificial selection
a form of directional selection analogous to natural selection, but without the competitive element
migration
the movement of individuals from one population to another
sexual selection
promotes traits that increase an individual’s access to reproductive opportunities
intersexual selection
focuses on the interactions between females and males
intrasexual selection
focuses on interactions between individuals of one sex
gene flow
the movement of alleles from one population to another
bottleneck
occurs when an originally larger population falls to just a few individuals
founder effect
when a few individuals start a new population
molecular evolution
evolution at the level of DNA, which in time results in the genetic divergence of populations
molecular clock
estimates of the time when different taxa diverged, based on the amount of genetic divergence between them
