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Chapter 23: The Evolution of Populations Flashcards

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207679567the smallest unit that evolvespopulation (not individuals)0
207679568microevolutionthe change in allele frequencies of a population1
210651924What was missing in Darwin's explanations?an understanding of inheritance that could explain how chance variations arise in a population while also accounting for the precise transmission of these variations from parents to offspring2
210651925Mendel's laws of inheritance were originally believed to beat odds with Darwin's theory of natural selection3
210651926What did Darwin believe regarding traits?he believed in quantitative characters, those characteristics in a population that vary along a continuum (i.e. fur length and speed at which an animal can flee from a predator)4
210651927What was Mendel's point of view regarding traits?he recognized only discrete "either-or" traits as heritable5
210651928population geneticsemphasizes the extensive genetic variation within a populations and recognizes im[importance of quantitative characters6
210651929quantitative charactersA heritable feature in a population that varies continuously as a result of environmental influences and the additive effect of two or more genes (polygenic inheritance).7
210651930modern synthesis(1940s) integrates ideas and discoveries from different fields like paleontology, taxonomy, biogeography, population genetics.8
210651931architects of modern synthesisTheodosius Dobzhansky (1900-1975), Sewall Wright (1889-1998), Ernst Mayr (1904-), Gaylord Simpson (1902-1984), G. Ledyard Stebbins (1906-2000)9
2106519323 emphasis of modern synthesis1. importance of populations as the units of evolution 2. the central role of natural selection as the most important mechanism of evolution 3. the idea of gradualism to explain how large changes can evolve as an accumulation of small changes occurring over long periods of time10
210651933populationlocalized group of individuals belonging to the same species11
210651934speciesa group of populations whose individuals have the potential to interbreed and produce fertile offspring in nature12
210651935individuals are more likely to breed withmembers of their own population rather then members of a different population13
210651936individuals near a population center are on average more closely related toone another than to members of other populations14
210651937gene poolthe total aggregate of genes in a population at any one time. consists of all alleles at all gene loci in all individuals of a population15
210651938homozygoustwo identical alleles for a given character16
210651939heterozygoustwo different alleles for a given character17
210651940If all members of a population are homozygous for the same allele, that allele isfixed in the gene pool18
210651941Hardy-Weinberg Theoremstates that the frequencies of alleles and genotypes in a population's gene pool remain constant over the generations unless acted upon by agents other than Mendelian segregation and recombination of alleles19
210651942Hardy-Weinberg Equilibriumcondition that occurs when the frequency of alleles in a particular gene pool remain constant over time20
210651943Hardy-Weinberg Equation(p squared) + 2pq + (q squared) = 1, where (p squared) = frequency of RR genotype, 2pq = frequency of Rr plus rR genotype, and (q squared) = frequency of rr genotype21
210651944connection between Hardy-Weinberg, Mendel, and DarwinNatural selection requires genetic variation, and the Hardy-Weinberg theorem explains how Mendelian inheritance preserves genetic variation from one generation to the next22
210651945Assumptions of Hardy-Weinberg Theorem1. Very large population size (small population can cause genetic drift) 2. No migration (gene flow) 3. No net mutations (alter gene pool by changing one allele into another) 4. Random mating 6. No natural selection (differential survival and reproductive success of genotypes will alter their frequencies)23
210651946Genetic driftthe chance fluctuation in the gene pool, can cause genotype frequencies to change over time24
210651947gene flowthe transfer of alleles between populations due to movement of individuals or gametes, can increase the frequency of any genotype that is in high frequency among immigrants25
210660701if the frequencies of alleles or genotypes deviate from values predicted by Hardy-Weinberg equation it is usually because..the population is evolving26
210660702evolution at the population levelevolution is a generation-to-generation change in a population's frequencies of alleles27
210660703main factors that cause microevolution (alter the allele frequencies in a population)genetic drift, natural selection, gene flow, mutation. Genetic drift and natural selection are the most important28
210660704Natural selection always has apositive effect on the population (the others can have positive, negative, or neutral effect)29
210660705what are two situations that can shrink a population down to a small enough size where genetic drift becomes a problem?bottleneck effect and founder effect30
210660706Bottleneck effectdisasters such as earthquakes, floods, droughts, and fires reduce the size of a population drastically, and the new population may not be representative of the original population. Often times by change certain alleles become over represented while others become under represented , and still some alleles may be eliminated all together. reduces overall genetic variability in a population31
210660707Founder effectwhen a few individuals from a larger population colonize in an isolated island, lake, or other new habitat. results in genetic drift. usually accounts for high frequency of certain inherited disorders32
210660708natural selectiondifferential success in reproduction among individuals in a population. accumulates favorable genotype in a population33
210660709mutationchange in an organism's nucleotide sequence in DNA, rare34
210660710both quantitative and discrete characters contribute tovariation within a population35
210660711most heritable variation consists ofquantitative characters that vary along a continuum within a population, usually indicates polygenic inheritance36
210660712polygenic inheritancecombined effect of two or more genes on a single phenotypic character,37
210660713discrete characterscan be classified on an either or basis, usually because they are determined by a single gene locus with different alleles that affect distinct phenotypes38
210660714morphsthe different forms when two or more forms of a discrete character are represented in a population39
210660715polymorphica population is said to be polymorphic for a characters if two or more distinct morphs are each represented in high enough frequencies to be readily noticeable40
210660716gene diversitygenetic variation at level of whole genes41
210660717nucleotide diversitygenetic variation at the molecular level42
210660718geographic variationdifferences in gene pools between populations or subgroups of populations43
210660719clinea type of geographic variation, a graded change in some trait along a geographic axis44
210660720new alleles originate only bymutation45
210660721where do mutations have to occur in order to produce gametes that can be passed along to offspring?cell lines46
210660722to what do members of a sexually reproducing population owe nearly all their genetic differences to?the unique recombinations of existing alleles each individual receives from the gene pool47
210660723how is variation preserved?diploidy and balanced polymorphism48
210660724diploidyhides genetic variation from selection in the form of recessive alleles in heterozygotes49
210660725balanced polymorphismthe ability of natural selection to maintain stable frequencies of two or more phenotypic forms in a population50
210660726heterozygote advantageif individuals who are heterozygous at a particular locus have greater survivorship and reproductive success than any homozygote, then two or more alleles will be maintained at the locus by natural selection51
210660727neutral variationconfers no selective advantage for some individuals over others (fingerprints), frequencies not affected by natural selection52
210660728frequency-dependent selectionthe survival and reproduction of any one morph declines if that phenotypic form becomes too common in a population53
210660729only a fraction of the extensive variation in a gene poolsignificantly affects organisms54
210660730Darwinian fitnessthe contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals55
210660731relative fitnessthe contribution of a genotype to the next generation compared to the contributions of alternative genotypes for the same locus56
210660732the relative fitness of an allele depends onthe entire genetic context in which it works57
210660733three selection trendsdirectional selection, diversifying selection, stabilizing selection58
210660734directional selectionmost common during periods of environmental change or when members of a population migrate to some new habitat with different environmental conditions. Shifts the frequency curve for variations in some phenotypic character in one direction or the other by favoring what are initially relatively rare individuals that deviate from the average for that character59
210660735diversifying selectionoccurs when the environmental conditions are varied in a way that favors individuals on both extremes of a phenotypic range over intermediate phenotypes60
210660736stabilizing selectionacts against extreme phenotypes and favors the more common intermediate variants. reduces variation and maintains that status quo for a particular phenotypic character61
210660737advantage of sexthe processes of meiosis and fertilization generate the genetic variation upon which natural selection can act as an agent of adaptation.62
210660738sexual dimorphismA special case of polymorphism based on the distinction between the secondary sex characteristics of males and females.63
210660739intrasexual selectionA direct competition among individuals of one sex (usually the males in vertebrates) for mates of the opposite sex.64
210660740intersexual selectionSelection whereby individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex; also called mate choice.65
210660741four reasons why natural selection cannot fashion perfect organisms1. Evolution is limited by historical constraints 2. Adaptations are often compromises 3. Not all evolution is adaptive 4. Selection can only edit existing variations66

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