A PARTIAL MAP OF LINKAGE GROUP D IN NEUROSPORA CRASSA

Abstract

The biochemical mutants used were arg (arginine), pdx (pyridoxine, not pH-sensitive), pyr 1 and pyr 2 (pyrimidine), pyr 3 (pyrimidine, temp.-sensitive), ad (adenine), hist (histidine), pan (panthothenic acid). The visible mutants were co(colonial), cot (colonial, temp.-sensitive, with normal growth at 25[degree] C and extreme colonial growth at 35[degree] C), dn (dingy, gray lumps in slant cultures, slow-growing, bunched and crinkled hyphae on agar surface). For two-point crosses (repulsion phase) counts were made of random ascospores germinated on minimal medium in Petri dishes and incubated at 25 or 35[degree] C. The distance between genes was obtained by taking twice the percentage of spores which were wild with respect to both mutants. Three groups of mutants were indicated, with close linkage within a group. The first group (co, arg, pyr 1, pyr 3, and pdx) was separated by 30 units from the second group (cot, pan, hist, ad) which was 23 units from the third group (dn, pyr 2). For three-point crosses involving dn, co and cot asci were dissected on minimal agar and the plates incubated at 25[degree] C to score dn and co, then at 35[degree] C to score cot. The gene order was centromere-co-cot-dn, with 13 units between co and the centromere. Random spore counts from crosses of double mutants to single mutants indicated the following order for the genes being tested pyr 1-pdx-co-arg-pyr 3. Pseudo-wilds from crosses having co in one parent could be distinguished from true wilds on minimal agar and were excluded from counts. In crosses involving cot and dn, the pseudo-wilds were not recognized in early crosses, but in later crosses they were separated from true wilds by growth type. By excluding the pseudo-wilds gene orders were detn. as follows: ad-pan-cot-hist; cot-pyr 2-dn.