Mutations and Mutants Phenotype: the observable characteristics of an organism designated by a capital letter followed by two small letters, with either a plus and minus superscript to indicate the presence or absence of that property His. Glut et al Genotype: The precise genetic make-up of an organism designated by three lower case letters followed by a capital letter(all in italics) indicating the particular gene involved: hisC, mutations in the hisc gene would be designated as hisEl, hisC2 et alMutations and Mutants • Phenotype:the observable characteristics of an organism – designated by a capital letter followed by two small letters, with either a plus and minus superscript to indicate the presence or absence of that property: His- , Glu+ et al • Genotype: The precise genetic make-up of an organism – designated by three lower case letters followed by a capital letter (all in italics) indicating the particular gene involved: hisC, mutations in the hisC gene would be designated as hisC1, hisC2 et al