Abstract
When homozygous in zygotes, mutant alleles at the peak locus in linkage group V of Neurospora crassa initiate aberrant asci that are nonlinear, in contrast to the linear asci characteristic of wild type. Most mutant alleles are recessive, inasmuch as crosses of the mutant strains with wild type give linear asci. However, five different mutant alleles, when heterozygous with the wild-type allele, act in varying degrees as zygote dominants, initiating both linear and nonlinear asci, the relative proportions depending on the allele. Five modifiers that act on the dominance relationships of at least one of the five possible heterozygotes of a dominant peak and its wild-type allele have been characterized, four of them having been obtained by selection directed against a phenocopy of these mutants induced by treatment of wild type with l-sorbose. The pattern of modifier specificity observed among the various dominant peak heterozygotes indicates that the phenotypic effects are produced by a complex relationship between the modifiers and the dominant peak alleles in relation to their wild-type allele. In all but two cases the direction of modification, where present, is towards decreasing the dominance of the mutant allele in the heterozygote, evidenced by an increase in the percentage of linear asci when compared with control data. The modifiers exert their maximum modification when they themselves are heterozygous with their wild-type alleles and when the dominant peak allele is heterozygous with its wild-type allele. No modification occurs when heterozygous modifiers are included in zygotes homozygous for a dominant peak allele, reinforcing the notion that the modifiers act on the dominance relationship existent between a dominant peak allele and its wild-type allele, rather than influencing some activity of the mutant allele itself. The modifiers have no detectable effect of their own on ascus morphology, since homozygous modifier zygotes initiate entirely linear asci when only wild-type alleles of peak are present in the zygotes. Their only detectable effect, other than dominance modification, appears to be in conferring sorbose resistance to the mycelium. The modifiers are unlinked to the peak locus, and, except for two of them, they are nonallelic.
Full Text
The Full Text of this article is available as a PDF (2.1 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- DE TERRA N., TATUM E. L. Colonial growth of Neurospora. Sorbose and enzymes alter the composition of the cell wall and induce morphological changes. Science. 1961 Oct 13;134(3485):1066–1068. doi: 10.1126/science.134.3485.1066. [DOI] [PubMed] [Google Scholar]
- Klingmüller W. Kreuzungs-Analyse Sorbose-resistenter Mutanten von Neurospora crassa. Mol Gen Genet. 1967;100(2):109–116. doi: 10.1007/BF00333598. [DOI] [PubMed] [Google Scholar]
- Mahadevan P. R., Tatum E. L. Relationship of the major constituents of the Neurospora crassa cell wall to wild-type and colonial morphology. J Bacteriol. 1965 Oct;90(4):1073–1081. doi: 10.1128/jb.90.4.1073-1081.1965. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Novak D. R., Srb A. M. Genetic alterations of ascus development in Neurospora tetrasperma. Genetics. 1971 Feb;67(2):189–199. doi: 10.1093/genetics/67.2.189. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Perkins D. D., Newmeyer D., Taylor C. W., Bennett D. C. New markers and map sequences in Neurospora crassa, with a description of mapping by duplication coverage, and of multiple translocation stocks for testing linkage. Genetica. 1969;40(3):247–278. doi: 10.1007/BF01787357. [DOI] [PubMed] [Google Scholar]