Gene conversion spectrum of 15 mutants giving post-meiotic segregation in the b2 locus of Ascobolus immersus

1978 ◽  
Vol 163 (3) ◽  
pp. 313-326 ◽  
Author(s):  
N. Paquette ◽  
J.-L. Rossignol
Keyword(s):  
Gene Conversion ◽  
Meiotic Segregation ◽  
Ascobolus Immersus ◽  
Conversion Spectrum

scholarly journals THE INTERGRADATION, GENETIC INTERCHANGEABILITY AND INTERPRETATION OF GENE CONVERSION SPECTRUM TYPES

Genetics ◽  
1979 ◽  
Vol 92 (1) ◽  
pp. 49-65
Author(s):  
Bernard C Lamb ◽  
Aglaia Ghikas
Keyword(s):  
Gene Conversion ◽  
Base Substitution ◽  
Meiotic Segregation ◽  
Wild Type ◽  
Conversion Frequency ◽  
Ascobolus Immersus ◽  
Asymmetric Hybrid ◽  
Type C ◽  
Conversion Spectrum ◽  
Type Strains

ABSTRACT In the Pasadena strains of Ascobolus immersus, the gene conversion propperties of 29 induced (nine UV, nine NG, and 11 ICR-170) and nine spontaneous white-ascospore mutations have been studied. Each mutant was cyossed to three types of derived wild-type strains; single mutants often gave very different conversion results in the three types of crosses, with any or all of the following changes in: percentage with post-meiotic segregation among aberrant-ratio asci; percentage with conversion to wild type among aberrant-ratio asci; and in total conversion frequency. — These results are compared with those of LEBLON (1972 a, b) from Ascobolus immersus and Yu-SUN, WICRRAMARATNE and WHITEHOUSE (1977) from Sordaria breuicollis. It is shown that conversion spectrum types are not necessarily distinct, but can completely intergrade, on the criteria of both post-meiotic segregation frequency and direction of correction. Genetic differences between strains in the present work resulted in much interchangeability of spectrum types for the same mutation in different crosses; e.g., from type C in one cross to type B/D type in another cross, although the mutation is presumably of the same molecular type (addition or deletion frame shift, or base substitution) in each cross. These changes of conversion properties for a given mutation in different crosses mean that previous interpretations of spectrum types in terms of specific conversion properties for various molecular types of mutation are inapplicable, or inadequate on their own, to explain the present data. Other factors, such as heterozygous cryptic mutations or conversion control genes, are probably involved. Because of asymmetric hybrid DNA formation, correction properties may differ from observed conversion properties.

scholarly journals Reciprocal exchanges instigated by large heterologies in the b2 gene of ascobolus are not associated with long adjacent hybrid DNA stretches.

Genetics ◽  
1988 ◽  
Vol 119 (2) ◽  
pp. 329-336
Author(s):  
T Langin ◽  
H Hamza ◽  
V Haedens ◽  
J L Rossignol
Keyword(s):  
Gene Conversion ◽  
Dna Sequence ◽  
Sequence Homology ◽  
Holliday Junctions ◽  
Holliday Junction ◽  
Mendelian Segregation ◽  
Ascobolus Immersus ◽  
Postmeiotic Segregation ◽  
Single Branch ◽  
Hybrid Dna

Abstract In the gene b2 of Ascobolus immersus, large heterologies increase the frequencies of reciprocal exchanges on their upstream border (corresponding to the high non-Mendelian segregation side). Tests were made to determine whether these reciprocal exchanges, instigated by large heterologies, resulted from the blockage of a Holliday junction bordering a hybrid DNA tract extending from the end of the gene to the heterology. Three types of experiments were performed to answer this question. In all cases, results did not correlate the presence of reciprocal exchanges instigated by large heterologies with the presence of adjacent hybrid DNA tracts. These reciprocal exchanges were rarely associated with postmeiotic segregation at upstream markers, they were not associated with gene conversion of a marker within the interval and their frequency was not decreased by decreasing the frequency of hybrid DNA formation in the gene. These results led to the proposal of the existence of a precursor to reciprocal exchange different from a single branch-migrating Holliday junction. This precursor migrates rightward and its migration is dependent on the DNA sequence homology. The existence of this precursor does not exclude that reciprocal exchanges resulting from the maturation of single Holliday junctions bordering adjacent hybrid DNA tracts could also occur.

scholarly journals Gene conversion: observations on the DNA hybrid models

1970 ◽  
Vol 15 (1) ◽  
pp. 55-64 ◽  
Author(s):  
Andrzej Paszewski
Keyword(s):  
Experimental Data ◽  
Gene Conversion ◽  
Hybrid Models ◽  
Crossing Over ◽  
Meiotic Segregation ◽  
Tetrad Analysis ◽  
Dna Models ◽  
Complex Picture ◽  
New Hypothesis ◽  
Hybrid Dna

SUMMARYSome features of gene conversion in fungi and their bearing on the hybrid DNA models are discussed. Available experimental data from tetrad analysis seem to give a more complex picture of polarity in intra-genic recombination and of the relations between conversion and post-meiotic segregation, and between conversion and crossing-over, than predicted by the models.A new hypothesis of the mechanism of gene conversion with special attention given to the aspect of asymmetry in this phenomenon is proposed as an alternative to the mechanism suggested by the DNA hybrid models.

New equations and a method for finding nine parameter values for two alleles at one locus to study gene conversion using Ascobolus immersus

Genome ◽  
1992 ◽  
Vol 35 (3) ◽  
pp. 421-427 ◽  
Author(s):  
B. C. Lamb ◽  
S. A. Zwolinski
Keyword(s):  
Gene Conversion ◽  
Control Factors ◽  
Dna Models ◽  
Ascobolus Immersus ◽  
Asymmetric Hybrid ◽  
Quantitative Analyses ◽  
Allele Segregation ◽  
Parameter Values ◽  
Quantitative Treatment ◽  
Hybrid Dna

A quantitative treatment is given for meiotic gene conversion with its parameters and equations for their interactions to determine allele segregation class frequencies from heterozygotes. The possible pairing of both pairs of nonsister chromatids in a bivalent at exactly the same point is included. Using sets of data from Ascobolus immersus, it is shown that values for all nine parameters for hybrid DNA models of recombination can be obtained using an iterative computer program. The accuracy of the values is estimated and the double-strand gap repair model is considered. The parameter values obtained invalidate most of the simplifications used in previous quantitative analyses of gene conversion data. They showed total bias in strand preference in asymmetric hybrid DNA formation and some bias in which type of chromatid is the invading one. There were slight differences in repair frequency between the two types of mispair and very large differences in the direction of repair. Conversion control factors had major effects on hybrid DNA formation and repair of mispairs.Key words: Ascobolus, gene conversion, quantitative analysis, recombination mechanisms.

Mechanism of gene conversion in Ascobolus immersus

1973 ◽  
Vol 122 (2) ◽  
pp. 165-182 ◽  
Author(s):  
G. Leblon ◽  
J. -L. Rossignol
Keyword(s):  
Gene Conversion ◽  
Ascobolus Immersus

scholarly journals Polarity of gene conversion and post-meiotic segregation at the buff locus in Sordaria brevicollis

1973 ◽  
Vol 22 (3) ◽  
pp. 279-289 ◽  
Author(s):  
D. J. Bond
Keyword(s):  
Gene Conversion ◽  
Meiotic Segregation ◽  
Wild Type ◽  
Heteroduplex Dna ◽  
Dna Models ◽  
Hybrid Dna

SUMMARYThe flanking markers of wild-type recombinant spores originating from crosses of spore colour mutants in Sordaria brevicollis were analysed. Recombinant asci were of two main types – either with one or with two wild-type spores. In most crosses the behaviour of flanking markers was significantly different for these two types of recombinant asci. The main differences were in the polarity of gene conversion (as inferred from parental outside marker combinations) and in the frequency of recombinant outside markers. These differences were interpreted in terms of hybrid DNA models of recombination and correction of heteroduplex DNA.

How many additional parameters in a conversion model can be evaluated using "corresponding-site" events?

Genome ◽  
1994 ◽  
Vol 37 (1) ◽  
pp. 179-180 ◽  
Author(s):  
J. R. S. Fincham
Keyword(s):  
Gene Conversion ◽  
Meiotic Cell ◽  
Conversion Model ◽  
Ascobolus Immersus ◽  
Two Parameters ◽  
Recent Claim

Contrary to a recent claim by B.C. Lamb and S.A. Zwolinski (1992), the frequencies of "corresponding-site" conversion events (all four chromatids involved in conversion at the same locus in the same meiotic cell) can be used to evaluate only two parameters not otherwise calculable: a coincidence parameter and the frequency of conversion-type events in which a normal 1:1 ratio is restored.Key words: Ascobolus immersus, gene conversion.

scholarly journals A Role for Synaptonemal Complex in Meiotic Mismatch Repair

2021 ◽  
Author(s):  
Karen Voelkel-Meiman ◽  
Ashwini Oke ◽  
Arden Feil ◽  
Alexander Shames ◽  
Jennifer Fung ◽  
...  
Keyword(s):  
Synaptonemal Complex ◽  
Gene Conversion ◽  
Mismatch Repair ◽  
High Throughput Sequencing ◽  
Central Element ◽  
Meiotic Segregation ◽  
Wild Type ◽  
Physical Context ◽  
A Genome ◽  
Mitotic Proliferation

During meiosis a large subset of interhomolog recombination repair intermediates form within the physical context of the synaptonemal complex (SC), a protein-rich structure assembled at the interface of aligned homologous chromosomes. However, the functional relationship between SC structure and homologous recombination remains poorly defined. In prior work we determined that tripartite SC is dispensable for recombination in S. cerevisiae; SC central element proteins Ecm11 and Gmc2 instead limit the number of recombination events. Here we report that while dispensable for recombination per se, SC central element proteins influence the processing of interhomolog recombination intermediates in a manner that minimizes errors in mismatch correction. Failure to correct mis-paired bases within heteroduplex at meiotic recombination sites leads to genotypically sectored colonies (post meiotic segregation events) arising from mitotic proliferation of mismatch-containing spores. We discovered an increase in post-meiotic segregation at the THR1 locus in cells lacking Ecm11 or Gmc2, or in the SC-deficient but crossover recombination-proficient zip1[Δ21-163] mutant. High-throughput sequencing of octad meiotic products revealed a genome-wide increase in recombination events with uncorrected mismatches in ecm11 mutants relative to wild type. Meiotic cells missing Ecm11 also display longer gene conversion tracts, but tract length alone does not account for the higher frequency of uncorrected mismatches. Interestingly, the per-nucleotide mismatch frequency is elevated in ecm11 mutants when analyzing all gene conversion tracts, but is similar between wild type and ecm11 if one considers only those events with uncorrected mismatches. Our data suggest that a subset of recombination events is similarly susceptible to mismatch repair errors in both wild type and ecm11 strains, but in ecm11 mutants many more recombination events fall into this inefficient repair category. Finally, we observe elevated post-meiotic segregation at THR1 in mutants with a dual deficiency in MutSγ-mediated crossover recombination and SC assembly, but not in the mlh3 mutant, which lacks MutSγ crossovers but has abundant SC. We propose that SC structure promotes efficient mismatch repair of joint molecule recombination intermediates resolved via both MutSγ-associated and MutSγ-independent pathways, and is the molecular basis for elevated post-meiotic segregation in both MutSγ crossover-proficient (ecm11, gmc2) and MutSγ crossover-deficient (msh4, zip3) strains.

DETECTION OF ABERRANT 4:4 ASCI IN ASCOBOLUS IMMERSUS

1978 ◽  
Vol 20 (1) ◽  
pp. 9-17 ◽  
Author(s):  
N. Paquette
Keyword(s):  
Gene Conversion ◽  
High Frequencies ◽  
Ascobolus Immersus ◽  
Very High Frequencies ◽  
Very High ◽  
Hybrid Dna

Ascopore and mycelium markers were used to detect the aberrant 4:4 asci of the mutation b2A4 of the b2 locus of Ascobolus immersus. Previous studies have shown that this mutation produces gene conversion events with many postmeiotic (30+:5 m and 5+:3 m) in addition to meiotic (2+:6 m and 6+:2 m) segregations. But the aberrant 4:4 asci could not be scored because the octads of this fungus are unordered. The asci were screened using round-spored and granular-spored mutants and confirmed with two mycelium markers, a brown mutant and a wave mutant. Very high frequencies of aberrant 4:4 asci were observed in each cross performed (more than 40% of the postmeiotic segregations). This suggested that both chromatids are very often implicated in the process of hybrid DNA formation at this site of the locus.

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