scholarly journals GENE CONVERSION AT THE GRAY LOCUS OF SORDARIA FIMICOLA: FIT OF THE EXPERIMENTAL DATA TO A HYBRID DNA MODEL OF RECOMBINATION

Genetics ◽  
1985 ◽  
Vol 109 (3) ◽  
pp. 599-610
Author(s):  
Angelos Kalogeropoulos ◽  
Pierre Thuriaux
Keyword(s):  
Experimental Data ◽  
Gene Conversion ◽  
Sampling Error ◽  
Linear Equations ◽  
Initiation Site ◽  
Crossing Over ◽  
Dna Strands ◽  
Sordaria Fimicola ◽  
Postmeiotic Segregation ◽  
Hybrid Dna

ABSTRACT A hybrid DNA (hDNA) model of recombination has been algebraically formulated, which allows the prediction of frequencies of postmeiotic segregation and conversion of a given allele and their probability of being associated with a crossing over. The model considered is essentially the "Aviemore model." In contrast to some other interpretations of recombination, it states that gene conversion can only result from the repair of heteroduplex hDNA, with postmeiotic segregation resulting from unrepaired heteroduplexes. The model also postulates that crossing over always occurs distally to the initiation site of the hDNA. Eleven types of conversion and postmeiotic segregation with or without associated crossover were considered. Their theoretical frequencies are given by 11 linear equations with ten variables, four describing heteroduplex repair, four giving the probability of hDNA formation and its topological properties and two giving the probability that crossing over occurs at the left or right of the converting allele.—Using the experimental data of Kitani and coworkers on conversion at the six best studied gray alleles of Sordaria fimicola, we found that the model considered fit the data at a P level above or very close (allele h4) to the 5% level of sampling error provided that the hDNA is partly asymmetric. The best fitting solutions are such that the hDNA has an equal probability of being formed on either chromatid or, alternatively, that both DNA strands have the same probability of acting as the invading strand during hDNA formation. The two mismatches corresponding to a given allele are repaired with different efficiencies. Optimal solutions are found if one allows for repair to be more efficient on the asymmetric hDNA than on the symmetric one. In the case of allele g1, our data imply that the direction of repair is nonrandom with respect to the strand on which it occurs.

scholarly journals Parameters in gene conversion: An algebraic analysis of the hybrid DNA model at the gray locus of Sordaria fimicola.

1982 ◽  
Vol 40 (1) ◽  
pp. 1-18 ◽  
Author(s):  
Angelos Kalogeropoulos ◽  
Pierre Thuriaux
Keyword(s):  
Experimental Data ◽  
Gene Conversion ◽  
Mismatch Repair ◽  
Complex Situation ◽  
Algebraic Analysis ◽  
Sordaria Fimicola ◽  
Postmeiotic Segregation ◽  
Aberrant Segregation ◽  
Three Factor ◽  
Hybrid Dna

SUMMARYWe have extended previous algebraic analyses of aberrant segregation at the gray locus of Sordaria fimicola (Whitehouse, 1965; Emerson, 1966; Fincham, Hill & Reeve, 1980) to the more complex situation where aberrant segregations are detected in three factor crosses involving two flanking markers. This algebra has been applied to seven gray alleles which have been extensively characterized for their pattern of gene conversion and postmeiotic segregation by Kitani & Olive (1967). It is based on seven major types of aberrant segregation which can be distinguished in the presence of flanking markers spanning the converting site, and allows us to use up to six parameters to describe hDNA formation and mismatch repair. We present solutions which predict a spectrum of aberrant segregation fitting the experimental data at the P > 0·05 level for six of the seven alleles tested. They are consistent with the following properties of hDNA at the gray locus: (1) the single stranded DNA transferred during hDNA formation has always the same chemical polarity. (2) hDNA is mostly, if not entirely, symmetric, and its probability of formation is constant over the whole gene. (3) Disparity in aberrant segregation is mostly, if not entirely due to disparity in mismatch repair.

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.

scholarly journals Inherited Differences in Crossing Over and Gene Conversion Frequencies Between Wild Strains of Sordaria fimicola From “Evolution Canyon”

Genetics ◽  
2001 ◽  
Vol 159 (4) ◽  
pp. 1573-1593
Author(s):  
Muhammad Saleem ◽  
Bernard C Lamb ◽  
Eviatar Nevo
Keyword(s):  
Genetic Variation ◽  
Gene Conversion ◽  
Spontaneous Mutation ◽  
Crossing Over ◽  
Natural Genetic Variation ◽  
Evolution Canyon ◽  
Wild Strains ◽  
Sordaria Fimicola ◽  
First And Second Generation ◽  
Consistent Direction

Abstract Recombination generates new combinations of existing genetic variation and therefore may be important in adaptation and evolution. We investigated whether there was natural genetic variation for recombination frequencies and whether any such variation was environment related and possibly adaptive. Crossing over and gene conversion frequencies often differed significantly in a consistent direction between wild strains of the fungus Sordaria fimicola isolated from a harsher or a milder microscale environment in “Evolution Canyon,” Israel. First- and second-generation descendants from selfing the original strains from the harsher, more variable, south-facing slope had higher frequencies of crossing over in locus-centromere intervals and of gene conversion than those from the lusher north-facing slopes. There were some significant differences between strains within slopes, but these were less marked than between slopes. Such inherited variation could provide a basis for natural selection for optimum recombination frequencies in each environment. There were no significant differences in meiotic hybrid DNA correction frequencies between strains from the different slopes. The conversion analysis was made using only conversions to wild type, because estimations of conversion to mutant were affected by a high frequency of spontaneous mutation. There was no polarized segregation of chromosomes at meiosis I or of chromatids at meiosis II.

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 M26 recombinational hotspot and physical conversion tract analysis in the ade6 gene of Schizosaccharomyces pombe.

Genetics ◽  
1994 ◽  
Vol 136 (1) ◽  
pp. 41-51
Author(s):  
C Grimm ◽  
J Bähler ◽  
J Kohli
Keyword(s):  
Schizosaccharomyces Pombe ◽  
Restriction Site ◽  
Initiation Site ◽  
Upstream Region ◽  
Crossing Over ◽  
The Mean ◽  
Postmeiotic Segregation ◽  
Restriction Site Polymorphisms ◽  
Hotspot Mutation ◽  
Conversion Tract

Abstract At the ade6 locus of Schizosaccharomyces pombe flanking markers have been introduced as well as five silent restriction site polymorphisms: four in the 5' upstream region and one in the middle of the gene. The mutations ade6-706, ade6-M26 (both at the 5' end) and ade6-51 (middle of the gene) were used as partners for crosses with the 3' mutation ade6-469. From these three types of crosses, wild-type recombinants were selected and analyzed genetically to assess association with crossing-over and physically to determine conversion tract lengths. The introduced restriction site polymorphisms (five vs. only one) neither influenced the pattern of recombinant types nor the distribution of conversion tracts. The hotspot mutation M26 enhances crossing-over and conversion to the same proportion. M26 not only stimulates conversion at the 5' end, but does this also (to a lower extent) at the 3' end of ade6 at a distance of more than 1 kb. The majority of meiotic conversion tracts are continuous and postmeiotic segregation of polymorphic sites is rare. Conversion tracts are slightly shorter with M26 in comparison with its control 706. The mean minimal length of tracts varies from 670 bp (M26) to 890 bp (706) to 1290 bp (51). It is concluded that M26 acts as an initiation site of recombination or enhances initiation of recombination. M26 does not act by termination of conversion. A region of recombination initiation exists at the 5' end of the ade6 gene also in the absence of the ade6-M26 hotspot mutation.

scholarly journals Genetic analysis of recombination at the g locus in Sordaria fimicola

1974 ◽  
Vol 24 (3) ◽  
pp. 251-279 ◽  
Author(s):  
H. L. K. Whitehouse
Keyword(s):  
Excision Repair ◽  
Dna Structure ◽  
Repair Process ◽  
Wild Type ◽  
Mismatch Correction ◽  
Co Conversion ◽  
Sordaria Fimicola ◽  
Comparison Of The Results ◽  
Postmeiotic Segregation ◽  
Hybrid Dna

SUMMARYInterallelie crosses of mutants at the grey (g) spore colour locus in Sordaria fimicola, heterozygous for flanking markers, give rise to a large number of aberrant ascus genotypes, 45 of which can arise through relatively simple events and have been chosen for study. These genotypes comprise 50–75% of the aberrant asci, depending on the mutants crossed.Comparison of the results from 10 pairwise crosses involving 7 alleles reveals that linked postmeiotic segregation and co-conversion decrease rapidly in frequency with increasing separation of the mutant sites.The data from reciprocally recombinant asci, from asci with normal segregation at one of the two mutant sites, and from flanking marker behaviour in one- and two-point crosses, agree with the Holliday-Sobell formulation, with the following additional features:(1) The nuclease, which nicks homologous polynucleotides and then degrades one of the two nicked chains when a mutant enters the hybrid DNA structure, can show preferential degradation of the mutant (or the wild-type) chain. In addition, a second nuclease is involved in the excision-repair process that introduces an additional preferential (marker specific) bias in the degradation of the mutant (or the wild-type) chain. This could explain why asci with odd-ratio conversion (5:3 and 3:5 ratios) sometimes show a different bias, as first reported by Emerson for Ascobolus, from those with even-ratio conversion (6:2 and 2:6 ratios), since the latter but not the former require, in addition, the action of a mismatch correction enzyme to account for them.(2) The migratory hybrid DNA structure which enters the gene at one end may be of a different size from that which enters from the other end.(3) Mismatch correction at the end of the hybrid DNA structure leads to a non-recombinant outside marker genotype and modifies the 1:1 ratio of parental:recombinant flanking markers that is otherwise found.

An initiation site for meiotic crossing-over and gene conversion in the mouse

10.1038/ng990 ◽  
2002 ◽  
Vol 32 (2) ◽  
pp. 296-299 ◽  
Author(s):  
Hélène Guillon ◽  
Bernard de Massy
Keyword(s):  
Gene Conversion ◽  
Initiation Site ◽  
Crossing Over

A general method for identifying correct solutions in the quantitative analysis of gene conversion data

1986 ◽  
Vol 28 (5) ◽  
pp. 701-711 ◽  
Author(s):  
Bernard C. Lamb
Keyword(s):  
Quantitative Analysis ◽  
Gene Conversion ◽  
Simulated Data ◽  
Not Given ◽  
Heterozygous Site ◽  
Simplifying Assumptions ◽  
Sordaria Fimicola ◽  
Recombination Gene ◽  
General Method ◽  
Hybrid Dna

Past attempts to obtain values for meiotic parameters relating to hybrid DNA formation and the correction of mismatched bases in hybrid DNA have not given unique solutions unless various simplifying assumptions were made. A method is given for identifying correct sets of solutions after calculating the frequency of hybrid DNA formation at a heterozygous site and using the fact that closely linked sites within a locus have very similar hybrid DNA formation frequencies. The method is illustrated with simulated data and Sordaria fimicola data; it can also show up incorrect assumptions in analysis. A method is suggested for assessing the importance of double-strand gaps in producing conversions.Key words: recombination, gene conversion, quantitative analysis.

scholarly journals ABSENCE OF INTERFERENCE IN ASSOCIATION WITH GENE CONVERSION IN SORDARIA FIMICOLA, AND PRESENCE OF INTERFERENCE IN ASSOCIATION WITH ORDINARY RECOMBINATION

Genetics ◽  
1978 ◽  
Vol 89 (3) ◽  
pp. 467-497
Author(s):  
Y Kitani
Keyword(s):  
Gene Conversion ◽  
The Other ◽  
Crossing Over ◽  
Conversion Event ◽  
Large Samples ◽  
Crossover Event ◽  
Reciprocal Recombination ◽  
Sordaria Fimicola

ABSTRACT From the analysis of large samples of gene conversion asci in the g locus of Sordaria fimicola, it was found that neither the conversion event itself nor conversion-associated recombination of flanking markers cause either chiasma or chromatid interference with crossing over in a neighboring interval. The presence of more than one kind of crossover event, one causing interference the other not, is considered. The existence of two kinds of gene loci, one of single-cistron composition and the other of multiple-cistron composition, is discussed in relation to reciprocal recombination within a locus.

Sign in / Sign up

Export Citation Format

Share Document