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 )