scholarly journals THE INSTABILITY OF NEUROSPORA DUPLICATION Dp(IL⇒IR)H4250, AND ITS GENETIC CONTROL

Genetics ◽  
1977 ◽  
Vol 85 (3) ◽  
pp. 461-487
Author(s):  
Dorothy Newmeyer ◽  
Donna R Galeazzi
Keyword(s):  
Mating Type ◽  
Pericentric Inversion ◽  
Crossing Over ◽  
Chromosome Break ◽  
Vegetative Incompatibility ◽  
Type Locus ◽  
Normal Sequence ◽  
Two Factors ◽  
Break Points ◽  
As If

ABSTRACT Previous work (Newmeyer and Taylor 1967) showed that a nontandem duplication, Dp(IL→IR)H4250, is regularly produced by recombination in crosses heterozygous for the effectively terminal pericentric inversion In(IL→IR)H4250. The duplications initially have strongly inhibited growth because they are heterozygous for mating type, which behaves like a vegetative-incompatibility (het) locus. Such cultures "escape" from the inhibition as a result of events that eliminate the mating-type heterozygosity. The product of a given escape event may be barren or fertile. (Neurospora duplications are characteristically barren; that is, when crossed, they make many perithecia but few ascospores.)—The present paper reports on a genetic analysis of the instability of Dp(IL→IR)H4250 . Most of the barren escape products behave as if due either to mitotic crossovers, which make mating type and distal markers homozygous, or to very long deletions which uncover mating type and all distal markers; presumably the latter would retain enough duplicated material to render them barren. It is difficult to distinguish between these two possibilities, but homozygosis seems more probable and has been clearly demonstrated in one case. Only a few barren escapes could be due to short deletions or to changes at the mating-type locus.—The fertile escape products appear to be euploid. Most of these behave as if they arose by precise deletion of one or the other duplicated segment, thus restoring one of the parental sequences. A large majority of the precise deletions restore normal sequence; only a few restore inversion sequence. Preferential restoration of the normal sequence has also been found by other workers for Neurospora duplications from several other rearrangements. A hypothesis is presented to explain these findings; it is posulated that the precise deletions result from mitotic crossing over in homologous material located at chromosome tips and tip-break-points.—There is a smaller group of fertile escapes that are unlike either parental sequence; at least one of these involves a chromosome break outside the duplicated region.—Duplications in which the vegetative incompatibility is suppressed by the unlinked modifier tol are extremely barren; they only rarely lose a duplicated segment so as to become fertile.—The instability of Dp(IL→IR)H4250, with and without tol, is markedly altered by factors in the genetic background. The two factors studied in detail have qualitatively different effects.

AN INSERTIONAL TRANSLOCATION IN NEUROSPORA THAT GENERATES DUPLICATIONS HETEROZYGOUS FOR MATING TYPE

Genetics ◽  
1972 ◽  
Vol 71 (1) ◽  
pp. 25-51
Author(s):  
David D Perkins
Keyword(s):  
Mating Type ◽  
Meiotic Recombination ◽  
Pericentric Inversion ◽  
Break Point ◽  
Crossing Over ◽  
Wild Type ◽  
Normal Sequence ◽  
Donor Chromosome ◽  
Reversed Order ◽  
Insertional Translocation

ABSTRACT In strain T(I⇉II)39311 a long interstitial segment is transposed from IL to IIR, where it is inserted in reversed order with respect to the centromere. In crosses of T x T essentially all asci have eight viable, black spores, and all progeny are phenotypically normal. When T(I⇉II)39311 is crossed by Normal sequence (N), the expected duplication class is viable while the corresponding deficiency is lethal; 44% of the asci have 8 Black (viable) spores and 0 White (inviable) spores, 41% have 4 Black: 4 White, and 10% have 6 Black: 2 White. These are the ascus types expected from normal centromere disjunction without crossing over (8B:0W and 4B:4W equally probable), and with crossing over between centromere and break point (6B:2W). On germination, 8B:0W asci give rise to only parental types—4 T and 4 N; 4B:4W asci usually give four duplication (Dup) progeny; and 6B:2W asci usually give 2 T, 2 N, 2 Dup. Thus one third of all viable, black ascospores contain duplications.—Recessive markers in the donor chromosome which contributes the translocated segment can be mapped by duplication coverage. Ratios of 2 Dominant: 1 Recessive νs. 1 Dominant: 2 Recessive distinguish location in or outside the transposed segment. Eleven loci including mating type have been shown to lie within the segment, and markers at four loci have been transferred into the segment by meiotic recombination. The frequency of marker transfer indicates that the inserted segment usually pairs with its homologue. Ascus types that would result from single exchanges within the insertion are infrequent, as expected if asci containing dicentric bridges usually do not survive.—Duplication ascospores germinate to produce distinctive inhibited colonies. Later these "escape" to grow like wild type, and genes that were initially heterozygous in the duplication segregate when escape occurs. As with duplications from pericentric inversion In(IL⇉IR)H4250 (Newmeyer and Taylor 1967), the initial inhibition is attributed to mating-type heterozygosity, and escape to a somatic event that makes mating type homoor hemizygous.—Twenty additional duplication-generating Neurospora rearrangements are listed and described briefly in an Appendix.

NEW DUPLICATION-GENERATING INVERSIONS IN NEUROSPORA

1969 ◽  
Vol 11 (3) ◽  
pp. 622-638 ◽  
Author(s):  
Barbara C. Turner ◽  
Cecile W. Taylor ◽  
David D. Perkins ◽  
Dorothy Newmeyer
Keyword(s):  
Mating Type ◽  
Break Point ◽  
Low Fertility ◽  
Type Locus ◽  
Complementary Product ◽  
Single Crossing ◽  
Group I ◽  
Distinctive Morphology ◽  
Phenotype Characteristic ◽  
Break Points

Inversion In(ILR)NM176 has one break point at the extreme right end of linkage group I and the other distal to mating type in the left arm. In crosses of Inversion × Normal the products of single crossing over within the inversion are complementary duplication-deficiency classes. One crossover product is viable, with a large segment of IL duplicated and the dispensable right tip presumably deficient. This class has low fertility and distinctive morphology. The complementary product has a large deficiency which results in a pair of white, inviable ascospores. Single exchanges within the heterozygous inversion thus produce asci with 6 Black: 2 White spores; four-strand double exchanges produce 4 B:4 W; and non-exchanges produce asci with 8 B:0 W. Approximate mapping of break points was accomplished by three-point crosses. Precise placement of the left break point between ser-3 and un(55701t), just left of mating type, is based on coverage of markers by the heterozygous duplication. No crossover has been obtained between mating type and the break point, despite extensive efforts. In(ILR)NM176 differs from the inversion In(ILR)H4250 described by Newmeyer and Taylor (1967) in one main respect: the mating type locus is included in the inverted segment of NM176. Consequently, when duplications are generated, the progeny are unisexual and do not have the unstable inhibited phenotype characteristic of H4250 duplication progeny, which are heterozygous for the mating type alleles A and a. Three other inversions which originated independently of In(ILR)NM176 resemble it closely and have similar or identical break points.

scholarly journals VEGETATIVE INCOMPATIBILITY AND THE MATING-TYPE LOCUS IN THE CELLULAR SLIME MOLD DICTYOSTELIUM DISCOIDEUM

Genetics ◽  
1979 ◽  
Vol 93 (4) ◽  
pp. 861-875
Author(s):  
Gillian E Robson ◽  
Keith L Williams
Keyword(s):  
Dictyostelium Discoideum ◽  
Mating Type ◽  
Genetic Basis ◽  
Slime Mold ◽  
Cellular Slime Mold ◽  
Vegetative Incompatibility ◽  
Type Locus ◽  
Mating Type Locus ◽  
Slime Mold Dictyostelium Discoideum ◽  
Cellular Slime

ABSTRACT The genetic basis of vegetative incompatibility in the cellular slime mold, Dictyostelium discoideum, is elucidated. Vegetatively compatible haploid strains form parasexual diploids at a frequency of between 10-6 and 10-5, whereas "escaped" diploids are formed between vegetatively incompatible strains at a frequency of ~10-8. There is probably only a single vegetative incompatibility site, which appears to be located at, or closely linked to, the mating-type locus. The nature of the vegetative incompatibility is deduced from parasexual diploid formation between wild isolates and tester strains of each mating type, examination of the frequency of formation of "escaped" diploids formed between vegetatively incompatible strains, and examination of the mating type and vegetative incompatibility of haploid segregants obtained from "escaped" diploids.

New mutations that suppress mating-type vegetative incompatibility in Neurospora crassa

Genome ◽  
1994 ◽  
Vol 37 (2) ◽  
pp. 249-255 ◽  
Author(s):  
Tia S. Vellani ◽  
Anthony J. F. Griffiths ◽  
N. Louise Glass
Keyword(s):  
Neurospora Crassa ◽  
Mating Type ◽  
Vegetative Incompatibility ◽  
Type Locus ◽  
Regulatory Locus ◽  
Mating Type Locus ◽  
Recessive Mutations ◽  
Incompatibility Locus ◽  
New Alleles ◽  
New Mutations

The mating-type locus in the ascomycete Neurospora crassa functions as a vegetative-incompatibility locus during asexual growth such that A + a heterokaryons and A/a partial diploids are inhibited in their growth. In this study, we sought mutations that suppress mating-type associated vegetative incompatibility by using A/a partial diploids. Mutants were selected as spontaneous escapes from inhibited growth. Suppressors were identified by selecting escapes that retained the capacity to mate with both A and a strains. The escaped partial diploids were then outcrossed to remove the duplication. Seven suppressors were identified that segregated as single, recessive mutations. All seven of the suppressors were shown to be allelic to a previously obtained suppressor, tol, by segregation analyses and heterokaryon tests. This result indicates that all seven mutations are new alleles of tol and suggests that tol is a key regulatory locus in the expression of mating-type associated vegetative incompatibility in N. crassa.Key words: vegetative incompatibility, mating type, suppressors, Neurospora.

Effects of thetolmutation on allelic interactions athetloci inNeurospora crassa

Genome ◽  
1997 ◽  
Vol 40 (6) ◽  
pp. 834-840 ◽  
Author(s):  
John F. Leslie ◽  
Carl T. Yamashiro
Keyword(s):  
Neurospora Crassa ◽  
Mating Type ◽  
Vegetative Compatibility ◽  
Vegetative Incompatibility ◽  
Type Locus ◽  
Mating Type Locus ◽  
Inneurospora Crassa ◽  
Incompatibility Reactions

A mutant at the tol locus of Neurospora crassa can suppress heterokaryon (vegetative) incompatibility associated with differences at the mating-type locus. We tested the ability of this allele to suppress the vegetative incompatibility reactions that can occur when strains differ at one of nine het loci (het-C, -D, -E, -5, -6, -7, -8, -9, and -10). We found no cases in which the tol mutant suppresses a heteroallelic het locus interaction. Thus, the interaction(s) that leads to vegetative incompatibility because of differences at the mating-type locus is distinct from the interaction(s) that leads to vegetative incompatibility because of differences at any of these nine het loci.Key words: heterokaryon, mating type, vegetative compatibility.

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