Chapter 3 Extensions to Mendel's Laws
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 1 Extensions to Mendel Extensions to Mendel ’s Laws Chapter 3
Sectionsto study3.1Extensions to Mendel for single-gene inheritancePairs of alleles show deviations from complete dominance andrecessiveness.Different forms of the gene are not limited to two alleles.One gene may determine more than one trait.3.2Extensions to Mendel for multifactorialinheritance3-2
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-2 Sections to study Sections to study 3.1 Extensions to Mendel for single 3.1 Extensions to Mendel for single-gene inheritance gene inheritance Pairs of alleles show deviations from complete dominance and Pairs of alleles show deviations from complete dominance and recessiveness recessiveness. Different forms of the gene are not limited to two alleles. Different forms of the gene are not limited to two alleles. One gene may determine more than one trait. One gene may determine more than one trait. 3.2 Extensions to Mendel for 3.2 Extensions to Mendel for multifactorial multifactorial inheritance inheritance
Mendelian pattern of inheritanceSingle-gene traitXYellowpeasGreenpeasTwo alleles(Q:eggs)(:pollen)Clear-cut dominance andrecessivenessAll yellowGenotypic ratio1:2:1Self-fertilizationPhenotypicratio3:16022yellow:2001green3:13-3
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-3 Mendelian Mendelian pattern of inheritance pattern of inheritance Single-gene trait gene trait Two alleles Two alleles Clear-cut dominance and cut dominance and recessiveness recessiveness Genotypic ratio 1: 2: 1 Genotypic ratio 1: 2: 1 Phenotypic ratio 3: 1 Phenotypic ratio 3: 1
Exceptions to Mendelian pattern ofinheritanceSingle-genetraitPairs ofalleles show deviationsfromcomplete dominance andrecessiveness.Differentforms of the gene are not limited totwo alleles.OnegenemaydeterminemorethanonetraitMultifactorialtraitTraits determined by two ormore genes, or by the interaction ofgenes with the environment.3-4
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-4 Exceptions to Exceptions to Mendelian Mendelian pattern of inheritance pattern of inheritance Single-gene trait gene trait Pairs of alleles show deviations from complete dominance and Pairs of alleles show deviations from complete dominance and recessiveness recessiveness. Different forms of the gene are not limited to two alleles. Different forms of the gene are not limited to two alleles. One gene may determine more than one trait. One gene may determine more than one trait. Multifactorial Multifactorial trait Traits determined by two or more genes, or by the interaction of Traits determined by two or more genes, or by the interaction of genes with the environment. genes with the environment
3.1 Extensions to Mendelfor single-gene inheritance3-5
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-5 3.1 Extensions to Mendel for single 3.1 Extensions to Mendel for single -gene inheritance gene inheritance
1.Dominanceis notalways completeCrosses between true-breeding strains can produce hybrids withphenotypes different from both parents.TypeofA/A1A2IA2A/A?hybridsDominanceA1is dominantto A2CompleteXA2isrecessivetoAA2is dominanttoA1Complete+AlisrecessivetoA2A1andA2areincompletelyIncompletedominant relative toeachotherAandA?arecodominantCodominant3-6Fig.3.2
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-6 1. Dominance is not always complete 1. Dominance is not always complete Crosses between true-breeding strains can produce hybrids with phenotypes different from both parents. Fig. 3.2
CodominanceFi hvbridsexpressthetraits of bothparentsPhenotypic ratios are the same as genotypic ratios.IncompletedominanceF1 hybrids express an intermediate phenotype that differsfrom bothparents. Neither allele is dominant or recessive to the other.Phenotypic ratios are the same as genotypic ratios.3-7
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-7 Codominance Codominance F1 hybrids express the traits of both parents. F1 hybrids express the traits of both parents. Phenotypic ratios are the same as genotypic ratios. Phenotypic ratios are the same as genotypic ratios. Incomplete dominance Incomplete dominance F1 hybrids express an intermediate phenotype that differs from b F1 hybrids express an intermediate phenotype that differs from both parents. Neither allele is dominant or recessive to the other. parents. Neither allele is dominant or recessive to the other. Phenotypic ratios are the same as genotypic ratios. Phenotypic ratios are the same as genotypic ratios
Codominant lentil coat patternsCodominanceCSSCXF1hybrids expressGametesthetraits of bothparents.PhenotypicratiosareXSCDCSCDF,(allidentical)the same asgenotypic ratios.OSF2CSCSCSCDCPCDCSCD1CScS(spotted):2CScP(spotted/dotted):1CPcP(dotted)Fig.3.4a3-8
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-8 Codominant Codominant lentil coat patterns lentil coat patterns Fig. 3.4a Codominance Codominance F1 hybrids express F1 hybrids express the traits of both the traits of both parents. parents. Phenotypic ratios are Phenotypic ratios are the same as the same as genotypic ratios. genotypic ratios
Codominant blood type allelesABABBloodTypeRedbloodcellAandBAsugarBsugasugarsAA-Fig.3.4b3-9
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-9 Codominant Codominant blood type alleles blood type alleles Fig. 3.4b
HOantigen (H substance)GalNActransferaseGaltransferase(IA)(IB)XBantigenAantigenGalNAc(N-acetylgalactosamine)N-AcetylglucosamineWLipidFucoseGlucoseGalactose3-10
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-10 H O antigen (H substance). A antigen B antigen N-Acetylglucosamine Fucose Glucose Galactose Lipid Gal transferase (IB ) GalNAc transferase (IA ) GalNAc(N-acetylgalactosamine )