The genetic and physical maps were derived from two entirely different types of data. Genetic distances between genes were determined by tetrad analysis. Distances for gene–gene and gene–centromere linkages are expressed in centimorgans (cM) and were calculated using a maximum-likelihood equation¹² which yields values for map distance, an interference parameter, and error calculations for these two parameters. Mapping results on more than 2,600 named genes are presented. Physical distances are calculated directly from the complete DNA sequence. The precise values of all parameters (both tetrad analysis results and chromosomal base-pair coordinates) are available from the SGD.

Associations between open reading frames (ORFs) and corresponding mutations were made using a set of hybridization filters, originally produced by L. Riles and M. Olson¹³, which are now available from the American Type Culture Collection (http://www.atcc.org/). Other such associations were made by complementation experiments using cloned DNA fragments and/or sequence analysis of mutants. The data for some of these associations are published, but the documentation for all of them can be found on SGD.

Now that the entire yeast genome sequence is available, most revisions of the map will consist of associations between a biological function and an ORF. These associations will often involve the study of mutants of the gene. In the past, such an association invariably resulted in the naming of the gene; this process is likely to continue until all of the genes have been associated with a function and have thereby acquired a name. Because the genetic and physical maps are unlikely to change significantly, we see no need for any future publications; rather, we expect the electronic version of the maps to evolve into increasingly accurate guides to S. cerevisiae biology.