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.

DOMINANT-AND-RECESSIVE EPISTASIS IN A HOMEOTIC MOSQUITO MUTANT

1976 ◽  
Vol 18 (4) ◽  
pp. 593-600
Author(s):  
Satish C. Bhalla
Keyword(s):  
Linkage Group ◽  
Wild Type ◽  
Pure Strain ◽  
Group Iii ◽  
Homeotic Mutant ◽  
Culex Pipiens Fatigans ◽  
Group I ◽  
Ratio Data ◽  
Independent Segregation ◽  
Selection For

Folowing selection for 15 generations a pure strain of a homeotic mutant spur was isolated from a Brazilian population of the mosquito Culex pipiens fatigans. Monohybrid crosses showed a 13:3 segregation indicating dominant-and-recessive epistasis for wild-type vs. spur. This implies that a dominant allele at one locus and a recessive at the other interact to produce the mutant phenotype. Dihybrid crosses with linkage group II markers yellow and ruby gave 39:13:9:3 ratios indicating independent segregation. However, the dihybrid cross with linkage group I marker maroon showed a highly significant departure from 39:13:9:3 ratio. Data available indicate that the phenotype spur is controlled by a dominant epistat in linkage group III and a recessive epistat (approximately 31.9 crossover units from maroon) in linkage group I.

CAENORHABDITIS ELEGANS DEFICIENCY MAPPING

Genetics ◽  
1984 ◽  
Vol 108 (2) ◽  
pp. 331-345
Author(s):  
D Christine Sigurdson ◽  
Gail J Spanier ◽  
Robert K Herman
Keyword(s):  
Caenorhabditis Elegans ◽  
Linkage Group ◽  
Ethyl Methanesulfonate ◽  
Single Site ◽  
Crossing Over ◽  
Wild Type ◽  
Nematode Caenorhabditis Elegans ◽  
Recessive Lethal ◽  
X Ray ◽  
New Mutations

ABSTRACT Six schemes were used to identify 80 independent recessive lethal deficiencies of linkage group (LG) II following X-ray treatment of the nematode Caenorhabditis elegans. Complementation tests between the deficiencies and ethyl methanesulfonate-induced recessive visible, lethal and sterile mutations and between different deficiencies were used to characterize the extents of the deficiencies. Deficiency endpoints thus helped to order 36 sites within a region representing about half of the loci on LG II and extending over about 5 map units. New mutations occurring in this region can be assigned to particular segments of the map by complementation tests against a small number of deficiencies; this facilitates the assignment of single-site mutations to particular genes, as we illustrate. Five sperm-defective and five oocyte-defective LG II sterile mutants were identified and mapped. Certain deficiency-by-deficiency complementation tests allowed us to suggest that the phenotypes of null mutations at two loci represented by visible alleles are wild type and that null mutations at a third locus confer a visible phenotype. A segment of LG II that is about 12 map units long and largely devoid of identified loci seems to be greatly favored for crossing over.

scholarly journals ISOLATION AND PROPERTIES OF SELENOMETHIONINE-RESISTANT MUTANTS OF NEUROSPORA CRASSA

Genetics ◽  
1974 ◽  
Vol 77 (4) ◽  
pp. 627-638
Author(s):  
Gregory S Chen ◽  
Robert L Metzenberg
Keyword(s):  
Resistant Mutant ◽  
Heat Stability ◽  
Temperature Sensitive ◽  
Wild Type ◽  
High Concentration ◽  
Type Locus ◽  
Group I ◽  
In The Wild ◽  
Resistant Mutants ◽  
Adenosylmethionine Synthetase

ABSTRACT Mutants resistant to selenomethionine were isolated, and their properties studied. Mapping studies indicate that the mutation sites are located near the eth-1r locus in linkage group I, about ten map units away from the mating type locus. The sites of new mutation are either allelic to or very close to eth-1r. They are resistant not only to selenomethionine but also to ethionine, while the ethionine-resistant mutant, eth-1r, is sensitive to selenomethionine. The selenomethionine-resistant mutants are also temperature-sensitive mutants. However, they can grow at higher temperatures in medium containing 1 M glycerol.—It is very unlikely that the resistance is due to a change in the permeability of the membrane. Aryl sulfatase of se-metr mutants is not repressed by a high concentration of methionine (5 mM), although inorganic sulfate (2 mM) still can cause total repression. The γ-cystathionase levels of the mutants are normal, but the S-adenosylmethionine synthetase levels are only one-tenth of that observed in the wild-type strain. The heat-stability of this enzyme in the mutant is also different from that of the wild-type enzyme suggesting that the mutation might affect the structural gene of S-adenosylmethionine synthetase.

scholarly journals NEUROSPORA TREHALASE AND ITS STRUCTURAL GENE

Genetics ◽  
1985 ◽  
Vol 110 (2) ◽  
pp. 217-227
Author(s):  
Christopher White ◽  
Deborah B Lee ◽  
Stephen J Free
Keyword(s):  
Molecular Weight ◽  
Linkage Group ◽  
Structural Gene ◽  
Gene Mutations ◽  
Free Medium ◽  
Wild Type ◽  
Group I ◽  
Normal Wild Type

ABSTRACT We have isolated Neurospora trehalaseless mutants and mapped the trehalase structural gene to linkage group I. The structural gene mutations not only affect thermostability and other characteristics of the enzyme but also affect the production of an inhibitor of the wild-type trehalase. The inhibitor appears to be the mutant trehalase. We suggest that the mutant subunits act as inhibitors by entering into the multimeric forms of the enzyme and altering the ability of the normal wild-type subunits to catalyze the cleavage of trehalose.—Wild type trehalase has been purified to near homogeneity, and its characteristics have been studied. It was purified as a tetramer, with each subunit having a molecular weight of 88,000.—We have studied the regulation of trehalase and found the production of trehalase to be glucose repressible. Cells begin to produce trehalase 60 min after being transferred to glucose-free medium.

scholarly journals Clustering of rDNA containing type 1 insertion sequence in the distal nucleolus organiser of Drosophila melanogaster: implications for the evolution of X and Y rDNA arrays

1988 ◽  
Vol 51 (3) ◽  
pp. 209-215 ◽  
Author(s):  
P. R. England ◽  
H. W. Stokes ◽  
R. Frankham
Keyword(s):  
Drosophila Melanogaster ◽  
Gene Clusters ◽  
Distal Portion ◽  
Nucleolus Organizer ◽  
Rrna Genes ◽  
Alternative Hypotheses ◽  
Nucleolus Organiser ◽  
Or Gene ◽  
Exchange Hypothesis

SummaryThe ribosomal RNAs produced by the multigene families on the X and Y chromosomes of Drosophila melanogaster are very similar despite the apparent evolutionary isolation of the X and Y chromosomal rDNA. X–Y exchange through the rDNA is one mechanism that may promote co-evolution of the two gene clusters by transferring Y rDNA copies to the X chromosome. This hypothesis predicts that the proximal rDNA of X chromosomes will be Y-like. Consequently, rDNA variants found only on the X chromosome (such as those interrupted by type 1 insertions) should be significantly clustered in the distal X nucleolus organizer. Proximal and distal portions of the X chromosome nucleolus organizer were separated by recombination between the inverted chromosomes In(1)scv2 (breakpoint in the centre of the rDNA) and In(1)sc4Lsc8R (no rDNA). Molecular analyses of the resulting stocks demonstrated that rRNA genes containing type 1 insertions were predominantly located on the chromosome carrying the distal portion of the X rDNA, thus confirming a prediction of the X–Y exchange hypothesis for the co-evolution of X and Y chromosomal rDNA. Distal clustering is not predicted by the alternative hypotheses of selection or gene conversion.

scholarly journals Location of factors enhancing crossing over on linkage group I of Neurospora

1973 ◽  
Vol 21 (2) ◽  
pp. 195-204
Author(s):  
Jenny Hargrave ◽  
S. F. H. Threlkeld
Keyword(s):  
Linkage Group ◽  
Distal Region ◽  
Proximal Region ◽  
Crossing Over ◽  
Group I ◽  
The Right

SUMMARYAn enhancement of cross-over frequencies previously reported by Newcombe & Threlkeld (1972) is shown to be due to two regions located on linkage group I, a few cross-over units to the right of the centromere. The distal region appears to be shorter than the proximal region, but equally effective in enhancing cross-over frequencies. The longer proximal region is readily divisable by cross-overs and probably spans several crossover units.

scholarly journals Enhancers of conidiation mutants in Aspergillus nidulans.

Genetics ◽  
1994 ◽  
Vol 137 (1) ◽  
pp. 79-85
Author(s):  
D H Gems ◽  
A J Clutterbuck
Keyword(s):  
Linkage Group ◽  
Aspergillus Nidulans ◽  
Double Mutant ◽  
Slight Modification ◽  
Temperature Sensitive ◽  
Permissive Temperature ◽  
Wild Type ◽  
Group V ◽  
Group I

Abstract Mutants at a number of loci, designated sthenyo, have been isolated as enhancers of the oligoconidial mutations at the medA locus. Two loci have been mapped: sthA on linkage group I, and sthB on linkage group V. Two probable alleles have been identified at each locus but two further mutants were unlinked to either sthA or sthB. Neither sthA nor sthB mutants have conspicuous effects on morphology on their own, nor could the sthA1 sthB2 double mutant be distinguished from wild type. Mutants at both loci also interact with the temperature-sensitive brlA42 mutant at the permissive temperature to give a phenotype described as "Abacoid." sthA1 also induces a slight modification of the phenotype of an abaA mutant. We conclude that sthenyo genes act mainly at the phialide stage of conidiation. We also describe the isolation of new medA mutants arising spontaneously as outgrowths on brlA42 colonies.

scholarly journals Chromosome rearrangements that involve the nucleolus organizer region in Neurospora.

Genetics ◽  
1995 ◽  
Vol 141 (3) ◽  
pp. 909-923
Author(s):  
D D Perkins ◽  
N B Raju ◽  
E G Barry ◽  
D K Butler
Keyword(s):  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Distal Segment ◽  
Nucleolus Organizer ◽  
Molecular Evidence ◽  
Chromosome 2 ◽  
Group V ◽  
Chromosome Sequence ◽  
Chromosome Arm ◽  
Donor Chromosome

Abstract In approximately 3% of Neurospora crassa rearrangements, part of a chromosome arm becomes attached to the nucleolus organizer region (NOR) at one end of chromosome 2 (linkage group V). Investigations with one inversion and nine translocations of this type are reported here. They appear genetically to be nonreciprocal and terminal. When a rearrangement is heterozygous, about one-third of viable progeny are segmental aneuploids with the translocated segment present in two copies, one in normal position and one associated with the NOR. Duplications from many of the rearrangements are highly unstable, breaking down by loss of the NOR-attached segment to restore normal chromosome sequence. When most of the rearrangements are homozygous, attenuated strands can be seen extending through the unstained nucleolus at pachytene, joining the translocated distal segment to the remainder of chromosome 2. Although the rearrangements appear genetically to be nonreciprocal, molecular evidence shows that at least several of them are physically reciprocal, with a block of rDNA repeats translocated away from the NOR. Evidence that NOR-associated breakpoints are nonterminal is also provided by intercrosses between pairs of translocations that transfer different-length segments of the same donor-chromosome arm to the NOR.

Meiotic analysis of induced mutations in Ophiostoma ulmi

1990 ◽  
Vol 68 (2) ◽  
pp. 232-235 ◽  
Author(s):  
L. Bernier ◽  
M. Hubbes
Keyword(s):  
Linkage Group ◽  
Dutch Elm Disease ◽  
Induced Mutations ◽  
Type Locus ◽  
Meiotic Analysis ◽  
Ophiostoma Ulmi ◽  
Group I ◽  
Disease Mutations ◽  
Nuclear Mutations ◽  
Additional Locus

Laboratory strains of Ophiostoma ulmi carrying nuclear mutations induced by exposure to N-methyl-N′-nitro-N-nitrosoguanidine were crossed, and the segregation of genetic markers was analyzed in random ascospore progeny. Investigation of 13 auxotrophic mutations and 1 benomyl-resistant mutation provided evidence for at least three linkage groups in O. ulmi. Five loci, identified by mutant alleles ade1-1, BENIR-1, cyi1-1, lys3-1, and nic1-1, were assigned to linkage group I, whereas markers ade2-1 and lys2-2 were mapped on linkage group II. An additional locus, Met1, was assigned to a third linkage group since mutant alleles at this locus segregated independently from markers on group I or II. The Ben1R locus, controlling resistance to benomyl, segregated independently from the mating type locus and thus appeared to differ from the Tol locus described by other workers. Key words: Ophiostoma ulmi, Dutch elm disease, mutations, linkage analysis.

scholarly journals Interspecific crosses and crossing-over in Neurospora

1972 ◽  
Vol 19 (2) ◽  
pp. 115-119 ◽  
Author(s):  
K. D. Newcombe ◽  
S. F. H. Threlkeld
Keyword(s):  
Linkage Group ◽  
Neurospora Crassa ◽  
Interspecific Crosses ◽  
Crossing Over ◽  
Centromere Region ◽  
Group I

SUMMARYThrough a series of backcrosses the centromere region of linkage group I of Neurospora crassa was transferred to the N. sitophila genome, and through another series of backcrosses the centromere region of linkage group I of N. sitophila was transferred to N. crassa. Strains thus synthesized showed, in further crosses, that the N. sitophila centromere region acts as a dominant enhancer of cross-over frequencies across linkage group I of the two species.

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