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Ultraviolet-sensitive mutants of Neurospora

I. Genetic basis and effect on recombination

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Three new UV-sensitive mutants were obtained using replica plating of the colonial crisp ragged strain of Neurospora crassa — uvs-3 (near cys-10, linkage group IVL), uvs-4 (4 units left of ad-4 IIIR) and uvs-5 (<1 unit from vel, IIIR). These are genetically distinct from uvs-1 (Chang and Tuveson, 1967) and uvs-2 (IVR, Stadler and Smith, 1968). They are two to three times more sensitive to UV than wild type. Heterokaryons between any two mutations are not sensitive, showing that all three are recessive. In heterozygous condition, none of the mutants affects crossing over. In homozygous condition, uvs-4 does not affect gene conversion as measured by prototroph frequency in crosses of pan-2 (B2) x pan-2 (B36), nor does it affect crossing over between cot-1 and tryp-4. Neither uvs-3 nor uvs-5 is fertile in homozygous crosses; asci do not develop beyond the multinucleate ascogenous hypha stage. — Mitotic effects were studied using strains haploid for UV-sensitivity but duplicated and heterozygous for mating type. In(ILR) H 4250 and Tp(I→II) 39311 were used to generate such duplications. Release from a slow-growing phenotype occurs when a mitotic event makes mating type homo-or hemizygous. With uvs-3, but not uvs-4 or uvs-5, release occurs 2 days earlier than in controls. Thus uvs-3 may affect chromosome breakage or mitotic recombination. The number of chromosome rearrangements present in a sample of colonies grown from single conidia of uvs-3 stocks is the same as in controls, but in test crosses 13% of the colonies produced barren perithecia of a type that is characteristic of duplications.

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A portion of a dissertation submitted to the Graduate Division of Stanford University in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

This work was supported by a National Science Foundation predoctoral fellowship and Public Health Service Research grant AI-01462.

Communicated by E. Witkin

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Schroeder, A.L. Ultraviolet-sensitive mutants of Neurospora . Molec. Gen. Genet. 107, 291–304 (1970).

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  • Recombination
  • Linkage Group
  • Ascus
  • Mating Type
  • Chromosome Rearrangement