Incomplete dominance in snapdragonsIncompletedominanceF1 hybrids express anAAaaXintermediatephenotypethat工differs from both parents.Gametesa2Neither allele is dominant orrecessiveto the otherPhenotypicratios are theAaF,(allidentical)AaXsame as genotypic ratios.a)Antirrhinum majus(snapdragons)A5F2AAAaAaaa1AA(red):2Aa(pink):1aa (white)Fig.3.33-11
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-11 Incomplete dominance in snapdragons Incomplete dominance in snapdragons Incomplete dominance Incomplete dominance F1 hybrids express an F1 hybrids express an intermediate phenotype that intermediate phenotype that differs from both parents. differs from both parents. Neither allele is dominant or Neither allele is dominant or recessive to the other. recessive to the other. Phenotypic ratios are the Phenotypic ratios are the same as genotypic ratios. same as genotypic ratios. Fig. 3.3
Incomplete dominance arises when phenotype varies inproportion to the amount of functional proteinR+/ R+R+/r00/ro050100EnzymeFig.8.303-12
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-12 Incomplete dominance arises when phenotype varies in Incomplete dominance arises when phenotype varies in proportion to the amount of functional protein. proportion to the amount of functional protein. Fig. 8.30
Do variations on dominance relations negateMendel's law of segregation?Mendel's law of segregation still applies.Dominance relations do not affect the segregation of allelesDominance relations only affect phenotype. Gene products controlexpression of phenotypes differently3-13
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-13 Do variations on dominance relations negate Do variations on dominance relations negate Mendel’s law of segregation? s law of segregation? Mendel’s law of segregation still applies. s law of segregation still applies. Dominance relations do not affe Dominance relations do not affect the segregation of alleles. ct the segregation of alleles. Dominance relations only affect phenotype. Dominance relations only affect phenotype. Gene products control expression of phenotypes differently. Gene products control expression of phenotypes differently
2.A gene may have more than two allelesGenes may have multiple alleles in a populationHumanABObloodtypes:I（isoagglutinogen同族凝集原）PhenotypeGeneAntibodiesGenotypeRed blood cellsurfaceantigenin serumJAJAJAanti-BAAAiTBBJBJBBanti-AIBiJA,TBJABABAandBneitheri0ineitheranti-A andanti-B3-14
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-14 2. A gene may have more than two alleles 2. A gene may have more than two alleles Genes may have multiple alleles in a population. Genes may have multiple alleles in a population. Phenotype Phenotype Gene Genotype Genotype Red blood cell Red blood cell surface antigen surface antigen Antibodies Antibodies in serum in serum A IA IAIA A anti-B IAi B IB IBIB B anti-A IBi AB IA, IB IAIB A and B A and B neither neither O i ii neither neither anti-A and anti-B Human ABO blood types: I (isoagglutinogen 同族凝集原)
Each individual carries only two of the alternative allelesABObloodtype3alleles:A,B,andi6possibleABOgenotypesDominance or recessiveness is always relative to a second alleleABObloodtypeJAis completelydominant toi but codominant to B6genotypesgenerate4phenotypes3-15
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-15 Each individual carries only two of the alternative alleles. Each individual carries only two of the alternative alleles. ABO blood type ABO blood type 3 alleles: 3 alleles: IA, IB, and i 6 possible ABO genotypes 6 possible ABO genotypes Dominance or Dominance or recessiveness recessiveness is always relative to a second allele. is always relative to a second allele. ABO blood type ABO blood type IA is completely dominant to is completely dominant to i but codominant codominant to IB 6 genotypes generate 4 phenotypes 6 genotypes generate 4 phenotypes