Parental GenerationF,GenerationF2GenerationParental seedcoatTotal F2ApparentF,phenotypefrequenciespheno-patternincrosstypicParent1×Parent2andratiophenotypesHowtoestablish2967983:1marbled-1Xclearmarbled-1dominance relations123463:1marbled-2× clearmarbled-2between multiple alleles?2831073:1spottedclearspottedclear-1.7065223:1dottedXdottedPerformreciprocal crossesbetween pure breeding723:1marbled-1×.marbled-2272marbled-lines ofallphenotypes4991473:1marbled-1×spottedmarbled-1Establish dominance seriesmarbled-15493 :1Xdottedmarbled-11.59770marbled-2×dotted1823:1marbled-2spotted×dotted+spotted/dotted-1683391:2:1157Fig.3.6Dominanceseries:marbled-1>marbled-2>spotted=dotted>clear
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-16 How to establish How to establish dominance relations dominance relations between multiple alleles? between multiple alleles? Perform reciprocal crosses Perform reciprocal crosses between pure breeding between pure breeding lines of all phenotypes lines of all phenotypes Establish dominance series Establish dominance series Fig. 3.6
Mutations are the source of new allelesMultiple alleles arise spontaneously in nature due to chancealterationsingeneticmaterial-mutationsmutationWild-typeMutantformExample:humanβ-hemoglobinHemegroupSixthfunctionβ Chain ofBBcodeHemoglobinGAGHbAnormalHbsGTGsickledHbCAAGabnormal3-17Fig.9.la,b
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-17 Mutations are the source of new alleles Mutations are the source of new alleles Multiple alleles arise spontaneously in nature due to chance Multiple alleles arise spontaneously in nature due to chance alterations in genetic material alterations in genetic material – mutations. mutations. Wild-type Mutant form mutation Example: human -hemoglobin Chain of Chain of Hemoglobin Hemoglobin Sixth code function function HbA GAG normal HbS GTG sickled sickled HbC AAG abnormal abnormal Fig. 9.1a, b
Mutation rate varies from1in10,000 to1in1,000,000 pergametepergeneration.Allele frequency is the percentage of the total number of genecopies represented byone allele.Wild-type allele-allele whose frequency is more than 1%Mutant allele-allelewhosefreguencyisless than1%Monomorphic-gene with only one wild-type allelePolymorphic-gene with more than one wild-type allele3-18
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-18 Mutation rate varies from 1 Mutation rate varies from 1 in 10,000 to 1 in 1,000,000 per in 10,000 to 1 in 1,000,000 per gamete per generation. gamete per generation. Allele frequency Allele frequency is the percentage of the total number of gene is the percentage of the total number of gene copies represented by one allele. copies represented by one allele. Wild-type allele type allele – allele whose frequency is more than 1%. whose frequency is more than 1%. Mutant allele – allele whose frequency is less than 1%. whose frequency is less than 1%. Monomorphic Monomorphic – gene with only one wild gene with only one wild-type allele. type allele. Polymorphic Polymorphic – gene with more than one wild gene with more than one wild-type allele. type allele
The mouse agouti gene: one wild-type allele,manymutantalleles (>14)(a)Musmusculus(housemouse)coatcolorsBlackhairCharles River Laboratories(b)AllelesoftheagoutigeneGenotypePhenotypeAgoutihairA-agoutiatatblack/yellowblackaaatablack/yellow3-19Fig.3.7a-b
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-19 The mouse The mouse agouti gene: one wild gene: one wild-type allele, type allele, many mutant alleles ( many mutant alleles (> 14) Fig. 3.7a-b
(c)Evidenceforadominanceseriesagoutiagoutiblackback/yellowbellyXatatAatAAagoutiblackagoutiXAAAaaablackback/yellowbellyblackback/yellowbellyblackXatatataaaDominanceseries:A>at>a3-20Fig.3.7c
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-20 Fig. 3.7c