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.

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.

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.

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.

scholarly journals Two locally acting genetic controls of gene conversion, ccf-5 and ccf-6, in Ascobolus immersus

1984 ◽  
Vol 43 (2) ◽  
pp. 107-121 ◽  
Author(s):  
W. M. Howell ◽  
B. C. Lamb
Keyword(s):  
Gene Conversion ◽  
Major Effect ◽  
Control Factor ◽  
Homozygous State ◽  
Initiation Point ◽  
Control Factors ◽  
Conversion Frequency ◽  
Ascobolus Immersus ◽  
Higher Eukaryotes ◽  
Hybrid Dna

SUMMARYTwo new conversion control factors (ccfs), ccf-5 and ccf-6, have been characterized in the Pasadena strains of Ascobolus immersus. Both are monogenic, with two known allelic forms (called A and B) of each factor, and affect the frequency of meiotic gene conversion at a white (w) ascospore locus closely linked to it, ccf-5 affecting w-9 and ccf-6 affecting w-BHj. The ccfs appear to be specific to their own target site, with no effect on at least nine unlinked w mutations. Conversion of the w locus affected was studied in + × w crosses with all four possible ccf arrangements: for example, for + × w-9, with ccf-5(A) in both parents, with ccf-5(B) in both parents, with ccf-5(A) in +, B in w-9, and with ccf-5(B) in +, A in w-9. For both ccfs, there were slight differences between crosses homozygous for A and those homozygous for B, and also slight differences between the two forms of heterozygous cross, A/B and B/A, but the major effect was for heterozygosity for the control factor to depress conversion frequency of the w locus, compared with either homozygous state. These two ccfs are compared with other sites affecting recombination in fungi and higher eukaryotes. Two possible modes of action of ccfs 5 and 6 are (i) on pairing closeness before hybrid DNA initiation, and (ii) on later stages such as the spread of hybrid DNA from an initiation point.

scholarly journals Non-locus-specific polygenes giving responses to selection for gene conversion frequencies in Ascobolus immersus.

Genetics ◽  
1995 ◽  
Vol 140 (4) ◽  
pp. 1277-1287
Author(s):  
S A Zwolinski ◽  
B C Lamb
Keyword(s):  
Gene Conversion ◽  
Major Effect ◽  
Control Factor ◽  
Minor Effect ◽  
Control Factors ◽  
Conversion Frequency ◽  
Ascobolus Immersus ◽  
Selection For ◽  
Postmeiotic Segregation ◽  
Or Genes

Abstract Selection for higher and lower meiotic conversion frequencies was investigated in the fungus Ascobolus immersus. Strains carrying the same known gene conversion control factors, which have major effects on conversion frequencies at their specific target locus, sometimes gave significant differences in conversion frequency. Selection for high or low conversion frequencies at the w1-78 site was practiced for five generations, giving significant responses in both directions. These responses were due to polygenes, or genes of minor effect, not to new conversion control factors of major effect. Crosses of selected strains to strains with other mutations showed that the genes' effects were not specific to w1-78, but could affect conversion frequencies of another mutation, w1-3C1, at that locus and of two other loci, w-BHj and w9, which are unlinked to w1 or to each other. The proportional changes in gene conversion frequency due to selection varied according to the locus and site involved and according to the conversion control factor alleles present. There were differences of > or = 277% in conversion frequency between "high" and "low" strains. Selection for conversion frequency had little effect on other features of conversion, such as the frequency of postmeiotic segregation or the relative frequencies of conversion to mutant or wild type.

scholarly journals A new type of genetic control of gene conversion, from Ascobolus immersus

1978 ◽  
Vol 32 (1) ◽  
pp. 67-78 ◽  
Author(s):  
B. C. Lamb ◽  
S. Helmi
Keyword(s):  
Gene Conversion ◽  
Genetic Control ◽  
Total Conversion ◽  
Position Effects ◽  
Homologous Chromosomes ◽  
Control Factors ◽  
Ascobolus Immersus ◽  
New Type ◽  
Asymmetric Hybrid ◽  
Hybrid Dna

SUMMARYA new type of genetic control of gene conversion is described from the Pasadena strains of the fungus Ascobolus immersus. It is characterized by cis/trans position effects and incomplete dominance. The P, K and 91 factors segregated from each other like Mendelian alleles and controlled the conversion frequencies and patterns of four nearby, closely-linked white ascospore colour mutations, although they did not usually coconvert with these w sites. Mutations of different origin responded similarly to the same control factors.These control factors greatly affected the total conversion frequencies, the relative frequencies of the different detected conversion classes and various other conversion parameters. The detailed results are consistent either with P, K and 91 affecting both the frequency of hybrid DNA formation and the correction processes for removing mispaired bases, or if they do not affect the correction processes directly, then they must have large effects on the frequency of asymmetrical hybrid DNA formation, which must usually be much more common than symmetric hybrid DNA, and there must be both an inequality in the frequency with which the two homologous chromosomes (in these crosses, + bearing and w bearing) invade each other, and in the frequency with which the two strands of each chromatid invade the homologue in asymmetric hybrid DNA formation.

scholarly journals Aberrant segregation patterns and gene mappability in Ascobolus immersus

1982 ◽  
Vol 39 (2) ◽  
pp. 121-138 ◽  
Author(s):  
G. Leblon ◽  
V. Haedens ◽  
A. Kalogeropoulos ◽  
N. Paquette ◽  
J.-L. Rossignol
Keyword(s):  
Wild Type ◽  
Mismatch Correction ◽  
Conversion Frequency ◽  
Ascobolus Immersus ◽  
Strong Map ◽  
Postmeiotic Segregation ◽  
The Relationship ◽  
Gene Maps ◽  
Aberrant Segregation ◽  
Hybrid Dna

SummaryCrosses between various types of mutant giving specific patterns of aberrant segregation were performed in the b2 spore colour locus of Ascobolus immersus. The map of 41 mutations showing various patterns of aberrant segregation was established. The frequency of wild-type recombinants and the map additivity, map expansion and map contraction characteristics were shown to be strongly dependent upon the pattern of aberrant segregation of the mutations used. Mutations giving no postmeiotic segregation and an excess of conversion to wild type over conversion to mutant exhibit map expansion in small intervals and a strong map contraction in large intervals. Mutations giving postmeiotic segregations also exhibit map contraction in large intervals. Mutations giving no postmeiotic segregations and an excess of conversion to mutant over conversion to wild type show map additivity and thus provide a simple way for devising gene maps. The relationship between the mapping properties and the pattern of aberrant segregations is accounted for when considering parameters of gene conversion: frequency and distribution of hybrid DNA, frequency and direction of mismatch correction.

scholarly journals A Role for Synaptonemal Complex in Meiotic Mismatch Repair

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

Abstract A large subset of meiotic recombination intermediates form within the physical context of synaptonemal complex (SC), but the functional relationship between SC structure and homologous recombination remains obscure. Our prior analysis of strains deficient for SC central element proteins demonstrated that tripartite SC is dispensable for interhomolog recombination in S. cerevisiae. Here we report that while dispensable for recombination per se, SC proteins promote efficient mismatch repair at interhomolog recombination sites. Failure to repair mismatches within heteroduplex-containing meiotic recombination intermediates leads to genotypically sectored colonies (post meiotic segregation events). We discovered increased post-meiotic segregation at THR1 in cells lacking Ecm11 or Gmc2, or in the SC-deficient but recombination-proficient zip1[Δ21-163] mutant. High-throughput sequencing of octad meiotic products furthermore revealed a genome-wide increase in recombination events with unrepaired mismatches in ecm11 mutants relative to wild type. Meiotic cells missing Ecm11 display longer gene conversion tracts, but tract length alone does not account for the higher frequency of unrepaired mismatches. Interestingly, the per-nucleotide mismatch frequency is elevated in ecm11 when analyzing all gene conversion tracts, but is similar between wild type and ecm11 if considering only those events with unrepaired mismatches. Thus, in both wild type and ecm11 strains a subset of recombination events is susceptible to a similar degree of inefficient mismatch repair, but in ecm11 mutants a larger fraction of events fall into this inefficient repair category. Finally, we observe elevated post-meiotic segregation at THR1 in mutants with a dual deficiency in MutSγ 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, and that absence of SC is the molecular basis for elevated post-meiotic segregation in both MutSγ crossover-proficient (ecm11, gmc2) and MutSγ crossover-deficient (msh4, zip3) strains.

scholarly journals Time-dependent changes in gene conversion inAscobolus immersus

1991 ◽  
Vol 57 (2) ◽  
pp. 97-103
Author(s):  
Shacker Helmi ◽  
Bernard C. Lamb
Keyword(s):  
Gene Conversion ◽  
Time Dependent ◽  
Initial Values ◽  
Conversion Frequency ◽  
Ascobolus Immersus ◽  
The Stability ◽  
Molecular Nature ◽  
Hybrid Dna

SummaryThe stability of conversion frequencies with time was investigated inAscobolus immersus. There were usually marked reductions in gene conversion frequencies at locuswlas crosses matured, to about one third of the initial values. This applied to all sixwlalleles tested, irrespective of their molecular nature, and at all temperatures used. Asci dehiscing early from an apothecium had much higher conversion frequencies than those dehiscing late, but there were no differences between apothecia maturing at different times within a cross. Alleles at four loci unlinked towlwere also tested. All four showed significant changes, though not in all crosses; three loci showed decreases in conversion frequency with time, while one showed an increase. The relative frequencies of different conversion classes often changed with time. These changes appear to result from alterations in locus-specific recombination initiation and in repair of base mispairs in hybrid DNA, not from differential maturation rates of different ascal segregation classes. These effects could cause misinterpretation of quantitative tests of recombination models from gene conversion data.

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