Basics of Bacterial Genetic Nomenclature

Genotypes. Bacterial genes are named using a standard genetic nomenclature originally proposed by Demerec. Each gene is assigned a three-letter designation, usually an abbreviation for the pathway or for the phenotype of mutants. To indicate genotype, the three-letter designation is written in lower case. (For example, mutations affecting lactose degradation are designated lac). Different genes that affect the same pathway are distinguished by a capital letter following the three-letter designation. (For example, the lacZ gene encodes the enzyme -galactosidase and the lacY gene encodes the enzyme lactose permease).

Each different mutation in the pathway is consecutively assigned a unique allele number. (For example, lacZ19 refers to a particular mutation that affects the lacZ gene. In order to distinguish each mutation, no other lac mutation, regardless of the gene affected, will be assigned the allele number 19). A separate series of allele numbers is used for each three-letter locus designation. The entire genotype is italicized or underlined (e.g. lacZ19).

Phenotypes. It is important to distinguish the phenotype of a strain from its genotype. The phenotype is usually indicated with the same three-letter designation as the genotype but phenotypes begin with a capital letter and are not italicized or underlined. (For example, strain TR251 [hisC527 cysA1349 supD] has a Cys+ His+ phenotype because the supD mutation suppresses the amber mutations in both the cysA and the hisC genes.)

More bacterial nomenclature. For a more detailed description of rules for bacterial genetic nomenclature download the following nomenclature pdf.

Yeast genetic nomenclature. The rules for genetic nomenclature for yeast and fungi differ from the rules for bacteria. For yeast genetic nomenclature, see

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Last modified July 15, 2002