Chapter 7 Anatomy and Function of a Gene: Dissection Through Mutation 7-1
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Sections to study7.1 Mutations: Primary tools of genetic analysisWhere do mutations come from?DNAdamagerepair7.2What mutations tell us aboutgene structure?7.3 What mutations tell us about gene function?7.4 A comprenensive exampie:Miutationstnataffectvision7-2
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 7-2 Sections to study Sections to study 7.1 Mutations: Primary tools of genetic analysis 7.1 Mutations: Primary tools of genetic analysis Where do mutations come from? Where do mutations come from? DNA damage repair DNA damage repair 7.2 What mutations tell us about gene structure? 7.2 What mutations tell us about gene structure? 7.3 What mutations tell us about gene function? 7.3 What mutations tell us about gene function? 7.4 A comprehensive example: Mutations that affect 7.4 A comprehensive example: Mutations that affect vision
Alternative forms of genes help trackinggenes in crossesRoundorwrinkledripeseedsYelloworgreenseedinteriorsGreenoryellowunripepodsPurpleorwhitepetalsAxialorterminalflowersLongorshortstemsInflatedorpinchedripepods7-3
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Wild-type allele: Anallele with a frequencyof morethan1%inapopulationMutant allele:Lessthan 1% in apopulation
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 7-4 Wild-type allele type allele: An allele with a frequency allele with a frequency of more than 1% in a of more than 1% in a population. population. Mutant allele Mutant allele: Less than 1% in a than 1% in a population. population
7.1Mutations:Primary tools of genetic analysisMutations are heritable changes in DNA seguences.Forward mutation - changes wild-type to a different allele.Reverse mutation (reversion)- causes mutation to revert backto wild-type.7-5
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 7-5 Mutations Mutations are heritable changes in DNA sequences. are heritable changes in DNA sequences. Forward mutation Forward mutation – changes wild changes wild-type to a different allele. type to a different allele. Reverse mutation Reverse mutation (reversion) (reversion)– causes mutation to revert back causes mutation to revert back to wild to wild-type. 7.1 Mutations: Primary tools of genetic analysis 7.1 Mutations: Primary tools of genetic analysis
Classification of mutations by theireffectonDNASubstitution - one nitrogenous base is replaced by oneofthe other threebases.Deletion-block of one or moreDNA pairs islost.Insertion-blockofone ormoreDNApairs is addedInversion-180rotation of aDNA segment.Reciprocal translocation-parts of nonhomologouschromosomeschangeplaces.7-6
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 7-6 Classification of mutations by their Classification of mutations by their effect on DNA effect on DNA Substitution Substitution – one nitrogenous base is replaced by one one nitrogenous base is replaced by one of the other three bases. of the other three bases. Deletion Deletion – block of one or more DNA pairs is lost. block of one or more DNA pairs is lost. Insertion Insertion – block of one or more DNA pairs is added. block of one or more DNA pairs is added. Inversion Inversion – 180 rotation of a DNA segment. rotation of a DNA segment. Reciprocal translocation Reciprocal translocation – parts of parts of nonhomologous nonhomologous chromosomes change places. chromosomes change places
Startingsequence(a)SubstitutionPurinesTransition:Purineforpurine,pyrimidineforpyrimidinePyrimidinesTransversion:Purineforpvrimidine,pvrimidirpurinePurinesPyrimidines(b)Deletion(c)Insertion7-7Fig.7.2
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(d)InversionSiteofinversion5'33'5'5335(e)ReciprocaltranslocationChromosome1Chromosome2ChromosomeB用图图器限品B会品零器员会会品breaksTranslocation7-8Fig.7.2
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Spontaneous mutations occur atavery low rateNumberofNumberofMutationLocusarate (×10-6)gametestestedmutations344.567,395a(albino)33.3919.699b-(brown)533.2150,391c-(nonagouti)1011.9839.447d-(dilute)416.4243,444In(leaden)252,220,37611.2(average)aMutationisfromwildtypetotherecessivealleleshown7-9Fig.7.3
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General observations of mutation ratesMutations affecting phenotype occurvery rarelyThe mutation rate varies from gene to gene.-Ranges from less than 10-9 to more than 10-3 per gene pergamete.The average rate is 2-12x10-per gene per gamete.The average rate in bacteria is 10-8 to10-7.The rate of forward mutation is almost always higherthan the rate of reverse mutation.7-10
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 7-10 General observations of mutation rates General observations of mutation rates Mutations affecting phenotype occur very rarely. Mutations affecting phenotype occur very rarely. The mutation rate varies from gene to gene. The mutation rate varies from gene to gene. Ranges from less than Ranges from less than 10-9 to more than to more than 10-3 per gene per per gene per gamete. gamete. The average rate is 2 The average rate is 2-1210-6 per gene per gamete. gamete. The average rate in bacteria is 10 The average rate in bacteria is 10-8 to 10-7. The rate of forward mutation is almost always higher The rate of forward mutation is almost always higher than the rate of reverse mutation. than the rate of reverse mutation