scholarly journals Evidence for Negative Interference: Clustering of Crossovers Close to the am Locus in Neurospora crassa Among am Recombinants

Genetics ◽  
1999 ◽  
Vol 152 (3) ◽  
pp. 965-969
Author(s):  
Frederick J Bowring ◽  
David E A Catcheside
Keyword(s):  
Neurospora Crassa ◽  
Molecular Evidence ◽  
Crossing Over ◽  
Negative Interference

Abstract In response to a conflict between two mapping studies in the predicted orientation of the allele map with respect to the centromere, Fincham proposed that recombination events at the Neurospora am locus rarely have an associated crossover. Fincham considered that the elevated levels of crossing over between flanking markers in am recombinants resulted from negative interference, an increased probability of a nearby second event, and on this basis predicted a clustering of crossing over near am in these recombinants. In this article we reevaluate the data from three mapping studies of the am locus and report molecular evidence that shows crossovers to be clustered immediately proximal to am in am recombinants.

scholarly journals The frequency in Neurospora tetrads of multiple exchanges within short intervals

1962 ◽  
Vol 3 (2) ◽  
pp. 315-327 ◽  
Author(s):  
David D. Perkins
Keyword(s):  
Neurospora Crassa ◽  
Aspergillus Nidulans ◽  
Crossing Over ◽  
Negative Interference ◽  
Short Intervals ◽  
Reciprocal Crossing ◽  
Chiasma Interference

Tetrad data from short gene-marked intervals provide information on the frequency of multiple exchanges within intervals. Non-parental ditype and tetratype frequencies from 58,000 interval-tetrads of Neurospora crassa show that 4-strand double exchanges are far less frequent than would be expected in the absence of chiasma or chromatid interference. These results are in general agreement with meiotic tetrad data from other organisms, except Aspergillus nidulans. They preclude the occurrence of reciprocal meiotic exchanges as clusters unless multiples within each cluster are restricted so as not to involve all four chromatids. If this is not the case, and chromatid interference does not occur, then chiasma interference must be strongly positive within short regions. Known cases of apparent negative interference among random meiotic segregants are probably the result of non-reciprocal conversion of a middle marker, rather than of multiple reciprocal crossing over.

scholarly journals Gene Conversion Alone Accounts for More Than 90% of Recombination Events at the am Locus of Neurospora crassa

Genetics ◽  
1996 ◽  
Vol 143 (1) ◽  
pp. 129-136 ◽  
Author(s):  
Frederick J Bowring ◽  
David E A Catcheside
Keyword(s):  
Molecular Markers ◽  
Neurospora Crassa ◽  
Gene Conversion ◽  
Holliday Junctions ◽  
Crossing Over ◽  
Gene Markers ◽  
General Significance ◽  
Flanking Sequences ◽  
Simple Conversion

Abstract We have used closely flanking molecular markers located ~4 kb distal and 6 kb proximal of the am locus to investigate the incidence of crossover events associated with the generation of prototrophic recombinants in a cross heteroallelic am1 am6. Ninety-three percent of prototrophs were generated by events that did not recombine the molecular markers, indicating that simple conversion accounts for the formation of most prototrophs and that associated crossovers are much less frequent (~0.07) than estimated previously using more distant flanking markers. This suggests that conversion and crossing over during meiosis may arise from distinct mechanisms or that if, as is widely supposed, conversion and crossing over result from alternate modes of resolution of Holliday junctions then, at least for the am locus of Neurospora, the mode of resolution is strongly biased in favor of retaining the parental association of flanking sequences. Because estimates of the association of conversion and crossing over based on more distant gene markers are similar for yeast and Neurospora (~0.35), our observation may have general significance.

scholarly journals CROSSING OVER AND NUCLEAR PASSING IN NEUROSPORA CRASSA

Genetics ◽  
1956 ◽  
Vol 41 (4) ◽  
pp. 610-622
Author(s):  
H Branch Howe
Keyword(s):  
Neurospora Crassa ◽  
Crossing Over

scholarly journals Crossing over between closely linked markers spanning the centromere of chromosome 3 inDrosophila melanogaster

1975 ◽  
Vol 26 (2) ◽  
pp. 173-185 ◽  
Author(s):  
Donald A. Sinclair
Keyword(s):  
Gene Conversion ◽  
Proximal Region ◽  
Chromosome 3 ◽  
Crossing Over ◽  
Negative Interference ◽  
Positive Correlation ◽  
Genetic Interval

SUMMARYRecombination in a short genetic interval spanning the proximal region of chromosome 3 was studied in the regionsst-in-ri-eg2-Ki-pp. Crossover frequencies in this region varied considerably in different genetic backgrounds; however, in all genotypes, the following observations were made: (1) an excess of multiple recombinant chromosomes indicative of high negative interference, was detected; (2) among the multiple recombi-nants, a positive correlation of simultaneous exchange in the most proximal and shortest adjacent genetic intervals was noted; (3) several classes of reciprocal products were not equally recovered. Three possible explanations for these results are: pre-meiotic exchange, chromatid interference and gene conversion.

Two kinds of "recombination nodules" in Neurospora crassa

Genome ◽  
1989 ◽  
Vol 32 (2) ◽  
pp. 309-317 ◽  
Author(s):  
Maja Bojko
Keyword(s):  
Neurospora Crassa ◽  
Synaptonemal Complex ◽  
Nucleolus Organizer ◽  
Crossing Over ◽  
Dramatic Reduction ◽  
Recombination Nodules ◽  
Exchange Event ◽  
The Mean ◽  
Different Origin ◽  
Positive Interference

Two morphological types of recombination nodules, termed early and late, are recognized in Neurospora crassa. Eighty nuclei at different substages were used to determine numbers of nodules per nucleus, distribution of nodules along the nucleolus-organizing chromosome, and distribution of nodules among the two largest chromosomes. Early nodules appear at the synaptonemal complex at early zygotene and increase in number during zygotene until a dramatic reduction occurs at zygotene – pachytene transition. Thereafter early nodules are steadily eliminated until they disappear by diplotene. Late nodules are also present during zygotene. Their number doubles at the zygotene – pachytene transition and stays at this level until diplotene. The total number of nodules is rather constant through zygotene and pachytene. Distribution of bivalents with 0, 1, 2, etc. nodules follows a Poisson distribution at zygotene, but not at pachytene, where variance is less than the mean, indicating positive interference. Nodules are distributed nonrandomly along the nucleolus-organizer bivalent. The pattern differs slightly in nuclei of different origin. Nuclei with unusual synaptonemal complexes sustain normal levels of recombination by having the same amount of nodules as normal nuclei. In abnormal nuclei nodules are preferentially associated with normal segments. It is proposed that early nodules do not participate in any form of recombination but have a role in finding an appropriate site for a crossing-over event. Morphological change to the late type indicates that the site has been reached and the exchange event can be mediated by the late nodule.Key words: recombination nodules, Neurospora crassa, synaptonemal complex.

scholarly journals Localized negative interference and its bearing on models of gene recombination

1960 ◽  
Vol 1 (1) ◽  
pp. 1-24 ◽  
Author(s):  
R. H. Pritchard
Keyword(s):  
Necessary Condition ◽  
Crossing Over ◽  
Short Segment ◽  
Cytological Evidence ◽  
Negative Interference ◽  
Sequence Of Events ◽  
Single Mechanism ◽  
The Mean ◽  
Reciprocal Process ◽  
Effective Pairing

In the analysis of recombination in Aspergillus nidulans coincidence values of about 1 are found in 3-point tests using markers more than a few map units apart. In comparable tests in which the marked intervals were very short (0·1 map unit or less), coincidence values of over 100 had been found. To account for this difference it was proposed that a necessary condition for recombination, termed ‘effective pairing’, was realized at any particular point on the chromosome in only a small fraction of a population of cells at meiosis. It was supposed that when effective pairing occurred it extended over a very short segment of the chromosome and that the probability of recombination in the effectively paired segment was high, i.e. about 1. Coincidence values greater than unity would be a necessary consequence of such a situation provided the intervals in question had a total length not much greater than that of effective pairing segments.The experiments described in this paper were undertaken in an attempt to measure the mean length of effectively paired segments, their distribution, and the frequency of exchange within them. The data suggest a mean length of about 0·4 map unit, a mean exchange frequency of about 0·6, and a distribution which is variable, perhaps random.The occurrence of localized negative interference suggests a way in which a number of difficulties encountered in relating the experimental evidence concerning the time and mechanism of recombination with the cytological evidence concerning the sequence of events at meiosis might be resolved. The data indicate that the frequency of recombination between linked loci is a measure principally of the frequency of effective pairing between them. If effective pairing is synonymous with homologous contact between chromosomes, and evidence is presented which suggests this may be the case, it becomes possible to construct a simple model which is compatible with the view that recombination takes place before chromosomes are paired, in the cytologically observable sense (i.e. before zygotene), at meiosis.The recombination events occurring within effectively paired regions are generally, although possibly not exclusively, reciprocal. Non-reciprocal recombinants have been encountered in Aspergillus and other organisms, characterized by the occurrence of 3:1 ratios in tetrads. On the basis of evidence currently available it does not seem necessary to invoke a special mechanism of recombination, distinct from crossing over, to account for the formation of non-reciprocal recombinaiits. A single mechanism of recombination of the copy-choice type which, although primarily a reciprocal process, is nevertheless not necessarily exactly so or always so in detail, will account for the observed results.

Variation in "Map Distance" in Neurospora crassa

1969 ◽  
Vol 15 (6) ◽  
pp. 623-627 ◽  
Author(s):  
Mary B. Mitchell
Keyword(s):  
Life Cycle ◽  
Neurospora Crassa ◽  
Crossing Over ◽  
General Behavior ◽  
Phenotype Distribution ◽  
Random Distributions ◽  
Detailed Interpretation ◽  
Chromosome Segments ◽  
Map Distance

Determinations of the same map distance in different crosses often give divergent results, whereas values for unrelated map regions are often strikingly similar. This situation has been examined in samples of serially isolated spore octets, mainly from two-marker crosses. Observed ratios of phenotype distribution classes suggest more systematic modifications of random distributions than would be expected from reassociations, through crossing-over, of chromosome segments chosen unsystematically. Detailed interpretation appears impracticable, since complexities in the general behavior of the organism indicate that the ratios observed may reflect opportunities, occurring at different stages of the life cycle, for successive reassociations of genetic units.

scholarly journals Genetic analysis of spontaneous half-sectored colonies ofSaccharomyces cerevisiae

1971 ◽  
Vol 18 (2) ◽  
pp. 179-184 ◽  
Author(s):  
J. R. Johnston
Keyword(s):  
Cell Division ◽  
Genetic Analysis ◽  
Mitotic Recombination ◽  
High Rate ◽  
Crossing Over ◽  
Diploid Strain ◽  
Negative Interference ◽  
Low Incidence

SUMMARYGenetic analysis of spontaneous half-sectored colonies of a diploid strain homozygous forade2and heterozygous for linked markersaro1A,hom2,ade8 and trp4was undertaken. Some of these were due to an unexpectedly high rate ofade2reversion and others to a low incidence of haploid sectors. About 50% resulted from mitotic recombination. Only a few were due to mitotic crossing over alone, the majority resulted from non-reciprocal ‘conversion’, including recombination extending over two loosely-linked loci, and some colonies featured both mitotic crossing over and mitotic conversion. The latter indicate that negative interference operates for mitotic recombination. The rate of mitotic recombination forade8, calculated from the frequency of half-sectored colonies was 3·1 × 10−4per cell division.

scholarly journals REVERSAL OF A NEUROSPORA TRANSLOCATION BY CROSSING OVER INVOLVING DISPLACED rDNA, AND METHYLATION OF THE rDNA SEGMENTS THAT RESULT FROM RECOMBINATION

Genetics ◽  
1986 ◽  
Vol 114 (3) ◽  
pp. 791-817
Author(s):  
David D Perkins ◽  
Robert L Metzenberg ◽  
Namboori B Raju ◽  
Eric U Selker ◽  
Edward G Barry
Keyword(s):  
Linkage Group ◽  
Distal Portion ◽  
Nucleolus Organizer ◽  
Rrna Genes ◽  
Molecular Evidence ◽  
Crossing Over ◽  
Wild Type ◽  
Type Locus ◽  
Group I ◽  
Chromosome Sequence

ABSTRACT In translocation OY321 of Neurospora crassa, the nucleolus organizer is divided into two segments, a proximal portion located interstitially in one interchange chromosome, and a distal portion now located terminally on another chromosome, linkage group I. In crosses of Translocation x Translocation, exceptional progeny are recovered nonselectively in which the chromosome sequence has apparently reverted to Normal. Genetic, cytological, and molecular evidence indicates that reversion is the result of meiotic crossing over between homologous displaced rDNA repeats. Marker linkages are wild type in these exceptional progeny. They differ from wild type, however, in retaining an interstitial block of rRNA genes which can be demonstrated cytologically by the presence of a second, small interstitial nucleolus and genetically by linkage of an rDNA restriction site polymorphism to the mating-type locus in linkage group I. The interstitial rDNA is more highly methylated than the terminal rDNA. The mechanism by which methylation enzymes distinguish between interstitial rDNA and terminal rDNA is unknown. Some hypotheses are considered.

scholarly journals Premeiotic change of nucleolus organizer size in Neurospora.

Genetics ◽  
1989 ◽  
Vol 122 (4) ◽  
pp. 783-791 ◽  
Author(s):  
D K Butler ◽  
R L Metzenberg
Keyword(s):  
Neurospora Crassa ◽  
Gel Electrophoresis ◽  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Nucleolus Organizer ◽  
Pulsed Field Gel Electrophoresis ◽  
Crossing Over ◽  
Tetrad Analysis ◽  
Homologous Chromosomes ◽  
Unequal Crossing Over

Abstract We have investigated the heritability of nucleolus organizer region (NOR) size in Neurospora crassa. By pulsed-field gel electrophoresis, we followed in genetic crosses the size of the normal or "terminal" NORs and the size of a small interstitial NOR. Tetrad analysis revealed that changes in NOR size occur frequently in the sexual phase. Moreover, most size changes occurred in the period between fertilization and meiosis, although some changes occurred during and after meiosis. Unexpectedly, increases and decreases in NOR size were not equally frequent: decreases were more common. The NOR size changes generated during meiosis were not the result of unequal crossing over between NORs on homologous chromosomes.

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