The Prt-2 locus is linked with Es-1 and Es-2 loci on chromosome 8 (linkage group XVIII). Recombination frequencies were 8.2% between Es-1 and Es-2 12.7% between Es-1 and Prt-2, and 4.5% between Es-2 and Prt-2. From these data, the map position of Prt-2 has been estimated on chromosome 8. The Prt-1 and Prt-3 loci, which are linked very closely on the same chromosome, were not determined.