GENETIC NOTATION

If a bacterial cell synthesizes amino acid leucine, it is represented as Leu+, and if it does not it is denoted as Leu+. The symbol has capitalized (not italicized) the letters. It denotes that Leu- has some defective genes which cripple the cell to synthesize leucine. The defective gene is represented as leu- (italicized three letters). However, if more than one gene are needed to synthesize leucine, it is denoted as leuA, leuB, etc. and the functional gene as leuA+ leuB, etc.

It should be kept in mind that the bacteria always have a single set of genes i.e. they are haploid. The eukaryotic organisms are haploid as well as diploid but the dominance of these two phases in the life of an organism differs. The diploid cells of organisms contain two sets of genes. The double sets of functional genes are represented as leu+/leu. They may have normal or defective gones. The functional form of a gene is called wild type.

However, if a bacterium is resistant to certain antibiotics it is represented by giving the symbols, for example Tet (resistant to tetracycline), Amp (resistant to ampicillin), Kan (resistant to Kanamycin), etc. the microorganisms susceptible to the above antibiotics are represented as Tet, Amp, Kan, etc.

Mutations occurring in genotype are also represented by numbers in the order in which they have been isolated. For example, if leucine mutation has occurred on 58 and 79 position it is written as leu58 and leu79 respectively. More specifically to denote the mutation on a particular gene e.g. A and B, it is written as leuA58 and leuB79 if mutation has occurred in leuA and leuB genes, respectively.