Bio Chapter 21

25 July 2022
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a generation-to-generation change in allele frequency.
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microevolution
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The original source of all genetic variation is _____.
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mutation
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According to the Hardy-Weinberg theorem, the frequencies of alleles in a population will remain constant if _____ is the only process that affects the gene pool.
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sexual reproduction
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does not change the frequency of alleles in the gene pool.
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sexual reproduction
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The evolutionary effects of genetic drift are greatest when _____.
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the population size is small
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What situation most likely explains the occasional high frequency of certain inherited disorders among human populations established by a small population?
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founder effect
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No two people are genetically identical, except for identical twins. The main source of genetic variation among human individuals is
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reshuffling of alleles due to sexual reproduction
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In evolutionary terms, an organism's fitness is measured by its _____.
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contribution to the gene pool of the next generation
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Blue poppies native to China were grown at a plant-breeding center in California. The plants with the thickest leaves were most likely to survive and reproduce in the drier climate. After several generations, the percentage of thick-leaved plants had increased by 42%. This adaptation of the poppies to their new environment is due to _____.
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directional selection
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What is the only evolutionary mechanism that consistently leads to adaptive evolution?
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natural selection
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_______ has a "sorting" effect, it consistently increases the frequency of alleles that improve the match between an organism and its environment.
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natural selection
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How does diploidy help to preserve genetic variation?
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It allows recessive alleles that may not be favored in the current environment to be preserved in the gene pool by propagation in heterozygotes.
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Natural selection tends to decrease
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genetic variation
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Recessive alleles are shielded from natural selection in
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heterozygotes
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does natural selection act on individuals or populations?
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individuals
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a change in allele frequencies in a population over generations
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microevolotion
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the mechanisms that cause allele frequencies to change
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natural selection, genetic drift, gene flow
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the transfer of alleles from one population to another
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gene flow
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which of the three causes adaptive evolution
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natural selection
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how genetic variation is measured at the molecular level
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nucleotide variability
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does nucleotide variability result in phenotypic variation?
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rarely
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how do you measure gene variability
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the average % of loci that are heterozygous
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What often reflects genetic variation
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phenotypic variation
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the product of inherited genotype and environmental influence
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phenotype
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natural selection can act on phenotypic variation that has a
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genetic component
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4 sources of genetic variation
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mutation, gene duplication, rapid reproduction, sexual reproduction
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ultimate source of genetic variation
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mutation
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only mutations in cells that produce _____ can be passed to offspring
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gametes
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one way that mutations can be helpful
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ones that alter protein production
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what equation can be used to test whether a population is evolving
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hardy weinberg equation
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the most important genetic variation for microevolution in populations
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allelic variation
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a localized group of individuals capable of interbreeding and producing fertile offspring
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population
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consists of all the alleles for all loci in a population (the sum of all alleles in a population)
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gene pool
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the location of a gene on a chromosome
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loci
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the relative quantity of a genotype for a gene in a population
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genotype frequency
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the relative quantity of an allele for one gene in a population
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allele frequency
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states that frequencies of alleles and genotypes in a population remain constant from generation to generation
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hardy weinberg principle
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allele frequencies will not change if
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gametes contribute to the next generation randomly
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what preserves genetic variation in a population
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mendelian inheritance
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the hardy weinberg principle describes a population that is
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not evolving
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describes the constant frequency of alleles in a not evolving population
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hardy weinberg equilibrium
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describes how allele frequencies fluctuate unpredictably from one generation to the next
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genetic drift
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tends to reduce genetic variation through losses of alleles
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genetic drift
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two examples of genetic drift
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founder effect and the bottleneck effect
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genetic drift that occurs when a few individuals become isolated from a larger population
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founder effect
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genetic drift that can result from a drastic decrease in population size due to a sudden environmental change
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bottleneck effect
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two examples of gene flow
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movement of reproductive individuals, movement of gametes
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the ability of alleles to be passed on to another generation
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fitness
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the only mechanism that consistently causes adaptive evolution
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natural selection
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an increase in the frequency of alleles that improve fitness
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adaptive evolution
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3 modes of natural selection
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directional selection, disruptive selection, stabilizing selection
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natural selection that favors individuals at one end of the phenotypic range
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directional selection
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natural selction that favors individuals at both extremes of the phenotypic range
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disruptive selection
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favors intermediate variants and acts on extreme phenotypes
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stabilizing selection
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natural selection for mating success
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sexual selection
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marked differences between the sexes in secondary sexual characteristics
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sexual dimorphism
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competition among individuals of one sex (usual males) for mates of the opposite sex
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intrasexual selection
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occures when individuals of one sex (usually females) are choosy in selecting their mates
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intersexual selection
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suggests that if a trait is related to male genetic quality of health, both the male trait and female preference for that trait should increase in frequency
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good genes hypothesis
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genetic variation that does not give a selective advantage or disadvantage
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natural variation
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heterozygotes can carry recessive alleles that are hidden from the effects of selection
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diploidy
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occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population
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balancing selection
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occurs when heterozygotes have a higher fitness than do both homozygotes
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heterozygote advantage
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occurs when the fitness of a phenotype declines if it becomes to common in the population
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frequency dependent selection