are molecules that reside in cells and carry genetic information. There are two types of nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are polymers of small nucleotide molecules, which are called bases and are arranged in variable sequences. Adenosine, cytosine, guanine, and thymine are the bases in DNA, whereas uracil replaces thymine in RNA. The sequence of these bases is unique for each gene in DNA. Codes for the arrangement of amino acids in the protein are specified by the gene.

In yeast, DNA is a fundamental part of the chromosomes in the nucleus, whereas in bacteria, it is a simple, twisted circle in the cytoplasm. This has consequences in the growth and organization of these two microorganisms and generally results in bacteria being faster growing than yeast.

The genetics of a cell depend on the genes specified in its DNA. The genes determine which proteins may be synthesized and thus dictate the structure and activities of the cell. Mutations in DNA change the cell and thus lead to the evolution of new strains and new species. In brewing yeast, mutations occur readily and can lead to changes in flavor, fermentability, and clarity. Such mutations tend to be undesirable, but they occasionally form the basis for new and novel beers. This said, relative genetic stability is one of the most desired qualities in brewer’s yeast, especially yeast that may be subject to repeated repitchings. Genetic stability holds the promise of repeatable results in healthy brewery fermentations.