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SUMMARYTwo colonial strains of Neurospora crmsa have been found suitable for testing nutritional requirements by replica plating. One strain (crisp) has been replicated with a set of needles and the other (crisp, ragged) with filter paper. When ripe perithecia from crisp x crisp crosses are submerged in water, complete asci can be collected rapidly with a capillary pipette.

HIS paper presents linkage data from crosses with markers in linkage group of Neurospora crassa (group D of HOULAHAN, BEADLE and CALHOUN 1949;MITCHELL and MITCHELL 1954). Most of these data were obtained in the course of constructing multiply marked stocks that would be suitable for experiments concerning environmental and nutritional effects on crossing over ( MALING 1959). Three new loci have been placed in the group, and additional information has been obtained regarding the relations of ten previously mapped loci. Group IV now contains a total of 23 gene loci-the largest number for any group in the complement except group I. All of the loci are located in one arm of the chromosome. According to ST. LAWRENCE (1952) this chromosome arm carries the nucleolus organizer; the cytological length of this arm is less than one third the total length of the chromosome (MCCLINTOCK 1945; SINGLETON 1953). Genes known to be in group IV are listed and documented in Table 1.In general, methods were as described in PERKINS 1959. The crosses reported here were all carried out on synthetic crossing medium at 25°C. The morphological mutants B57 (mat), B4 (ro-I : ropy-1) and B148 (col-4 : colonial-4) originated in experiments of DR. V. W. WOODWARD (see PERKINS 1959, Table 1). tryp-4 can be scored by ultraviolet fluorescence on supplemented minimal medium containing 10 pg/ml indole. EXPERIMENTAL RESULTSData from two-and three-point crosses are presented in Table 2. Results are summarized in the form of a map in Figure 1.Gene order: The present data have provided new information on the map relations of several genes. ro-I is shown to be closely linked to pan-I, while leu (37501 ) is some distance proximal to pan-I. mat is probably several units distal to pyr-2, and may thus be the rightmost gene marker in the group.Information on sequences in group IV has been published by a number of workers since the 1954 compilation of BARRATT, NEWMEYER, PERKINS and GARN-JOBST. The most extensive data were presented by MITCHELL and MITCHELL (1954), who considered the most probable order to be: centromerepyr-I pdx-I SUMMARYLinkage data have been obtained for 14 loci (including three that are new) in linkage group IV of Neurospora crassa, using random segregants obtained by nonselective methods, predominantly from 3-point crosses. All loci are in the same chromosome arm. Interference is apparently orthodox.