LIFESCI 4 Lecture Notes - Lecture 3: Woody Guthrie, Phenylketonuria, Phenylalanine
Document Summary
One allele is expressed and the other is not: incomplete dominance (partial) dominance: Phenotype of heterozygous hybrid is intermediate between homozygous parents. Genotypic ratio is 1:2:1 and so is the phenotypic ratio. Mendel"s laws are still valid at the genotypic level. Molecular explanation of one example of incomplete dominance. Pigment forming enzyme is present in limiting quantities, so having more makes the flowers more red. F1 hybrids differ from both parents and express an intermediate phenotype. Neither allele is dominant or recessive to the other. Phenotypic ratios are same as genotypic ratios: co-dominant alleles. Phenotypes of both alleles are observed in the heterozygotes. Blood cells with m and n antigens. F1 hybrids express phenotype of both parents equally. Phenotypic ratios are the same as genotypic ratios: multiple alleles. One gene but different alleles: it is sometimes difficult to distinguish between two situations:
