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bio 21
| Question | Answer |
|---|---|
| Modern genetics has elucidated the mechanisms of heredity.... | which were unknown to Darwin but which have provided the solid base that supports and substantiates his theory. |
| Allele frequencies | measure the amount of genetic variation in a population. |
| Genotype frequencies | show how a population’s genetic variation is distributed among its members. |
| how do Biologists estimate allele frequencies? | by measuring a sample of individuals from a population |
| The sum of all allele frequencies at a locus... | is equal to 1 |
| In a population at Hardy–Weinberg equilibrium... | allele frequencies remain the same from generation to generation...genotype frequencies remain in the proportions p2 + 2pq + q2 = 1 |
| Biologists can determine whether an agent of evolution is acting on a population ... | by comparing the genotype frequencies of that population with Hardy–Weinberg equilibrium frequencies |
| The evolutionary agents are | mutation, gene flow, genetic drift, nonrandom mating, and natural selection. |
| Most mutations are | are harmful or neutral to their bearers, but some are advantageous, particularly if the environment changes. |
| The origin of genetic variation | is mutation |
| Most mutations | are harmful or neutral to their bearers, but some are advantageous, particularly if the environment changes |
| Migration of individuals from one population to another, followed by breeding in the new location | gene flow |
| Immigrants may | add new alleles to a population or may change the frequencies of alleles already present |
| Random genetic drift | alters allele frequencies in all populations, but it overrides natural selection only in small populations |
| population bottlenecks | Organisms that normally have large populations may pass through occasional periods when only a small number of individuals survive. Those that survive may not be representative of the original population, and genetic variation may be reduced |
| New populations established by a few founding individuals can have gene frequencies that differ from those in the parent population | founder effect |
| frequencies of homozygous and heterozygous genotypes differ from Hardy–Weinberg expectations | If individuals mate more often with individuals that have the same or different genotypes than would be expected on a random basis—that is, when mating is nonrandom |
| Self-fertilization, an extreme form of nonrandom mating | reduces the frequencies of heterozygous individuals below Hardy–Weinberg expectations without changing allele frequencies. |
| Natural selection | is the only agent of evolution that adapts populations to their environments. Natural selection may preserve allele frequencies or cause them to change with time. Fitness is the relative reproductive contribution of a phenotype to subsequent generations |
| Stabilizing selection | which preserves average characteristics |
| directional selection | favors individuals that differ in one direction from the mean |
| disruptive selection | which favors individuals that differ in both directions from the mean |
| change in the distributions of phenotypes is governed by... | more than one locus |
| Sexual selection | can lead to the development of conspicuous traits |
| Intrasexual selection | is selection for features that enhance the ability of their bearers to compete for mates. Intersexual selection is selection for traits that make their bearers more attractive to the opposite sex. |
| Neutral mutations | accumulate within species |
| Random genetic drift, stabilizing selection, and directional selection | reduce genetic variation |
| most populations are genetically | highly variable |
| Sexual reproduction | generates an endless variety of genotypic combinations that increases the evolutionary potential of populations, but it does not influence the frequencies of alleles. |
| Sexual reproduction (2) | Rather, it generates new combinations of genetic material on which natural selection can act. |
| Frequency-dependent | selection occurs when the fitness of a particular phenotype depends on its frequency in the population |
| genetic variation within many species | is maintained in distinct subpopulations. |
| Adaptations to one set of conditions may involve _____ that reduce fitness to another set of conditions | trade-offs |
| . Short-term evolutionary | outcomes resulting from changes in allele frequencies |
| long-term evolutionary | outcomes resulting from infrequent or slow paced environmental factors. |
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