Heterokaryon Incompatibility Genes in NEUROSPORA CRASSA Detected Using Duplication-Producing Chromosome Rearrangements

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Evidence is presented for five or six previously undetected heterokaryon incompatibility (het) loci, bringing to about ten the number of such genes known in Neurospora crassa. The genes were detected using chromosome duplications (partial diploids), on the basis of properties previously known for het genes in duplications. Duplications homozygous for het genes are usually normal in growth and morphology, whereas those heterozygous are strikingly different. The heterozygotes are inhibited in their initial growth, produce brown pigment on appropriate medium, and later "escape" from their inhibition, as a result of somatic events, to produce wild-type growth.—Five normal-sequence strains were crossed to 14 duplication-producing chromosome rearrangements, and the duplication progeny were examined for properties characteristic of duplications heterozygous for known het genes. Each cross produced duplications for a specific region of the genome, depending on the rearrangement. Normal-sequence strains were wild types from nature, chosen from diverse geographic locations to serve as sources of genetic variation.—The duplication method was very effective. Most of the longer duplications uncovered het genes. The genes are: het-5 (on linkage group IR, in the region covered by duplications produced using rearrangement T(IR→VIR)NM103 ), het-6 (on IIL, covered by T(IIL→VI)P2869 and T(IIL→IIIR)AR18 duplications), het-7 (tentatively assigned to IIIR, T(IIIR→VIL)D305), het-8 (VIL, T(VIL→IR)T39M777 ), het-9 (VIR, T(VIR→IVR)AR209), and het-10 (VIIR, T(VIIR→IL)5936).

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