Taking advantage of the relative ease of detecting single wild-type animals among large numbers of Unc-54 mutant animals, rare intragenic recombinants were recovered between mutations of
unc-54 I, the gene coding for the myosin heavy chain of Caenorhabditis elegans body wall musculature. Appropriate closely linked marker mutations were used to improve screening efficiency, to distinguish recombination and conversion events, and to establish the relative order of
unc-54 mutations in the gene. From the analysis of more than 400 exceptional chromosomes recovered from tests involving 91 heteroallelic strains, 27
unc-54 mutations have been separated into ten distinct sites. Null mutations, comprising the majority of the mutations studied, are scattered throughout the map with the
e1300 and
st60 mutations located at the left and right ends, respectively. Three small deficiencies are clustered at an internal site nearer the left end. Two missense mutations lie to the right of these deficiencies. By correlating these results with molecular investigations of specific mutations, we conclude that the 5' end of the coding sequence is at the right end of the gene and is located distally on the chromosome. These correlations also demonstrate that the map includes at least 80% of the structural sequence. The genetic map allows us to infer the approximate location of mutations in the coding sequence, and should aid in the genetic dissection of