Abstract
The original foot-and-mouth diseases virus recombination map (Lake, Priston & Slade, 1975), which include 35 mutagen-induced ts mutants, has been extended both in detail and size by the mapping of a further 33 ts mutants (9 mutagen-induced and 24 spontaneous). The size increase from 0.57% to 3.27% maximum recombination fequency was principally due to the use of a new standardization technique for recombination fequencies but, in addition, the original map distance was increased by approx. 30% due to the mapping of new mutations. As in the original map, there was a marked concentration of mutations near the guanidine (gs) locus, i.e. 83% of the mutants had mutations in the third of the map adjacent to the gs locus.