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
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 7-7 Fig. 7.2 Purines G Pyrimidines C A T Purines A Pyrimidines T T A
(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
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 7-9 Spontaneous mutations occur at a very low rate Fig. 7.3
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