Three-to-one segregation from reciprocal translocation quadrivalents in Neurospora and its bearing on the interpretation of spore-abortion patterns in unordered asci

Genome ◽  
1995 ◽  
Vol 38 (4) ◽  
pp. 661-672 ◽  
Author(s):  
David D. Perkins ◽  
Namboori B. Raju
Keyword(s):  
Frequency Characteristic ◽  
Meiotic Division ◽  
Reciprocal Translocation ◽  
Visual Inspection ◽  
Chromosome Rearrangement ◽  
The Other ◽  
Sequence Information ◽  
Crossing Over ◽  
Distal Half ◽  
Basal Half

In Neurospora, viable ascospores become black (B) when mature, whereas ascospores that are deficient for a chromosome segment are inviable and usually fail to blacken. The presence of a chromosome rearrangement can be recognized and the type of rearrangement can usually be inferred by visual inspection of asci. When a cross is heterozygous for a reciprocal translocation, asci with eight black ascospores (8B:0W) and asci with eight abortive unpigmented ("white" (W)) ascospores (0B:8W) are theoretically produced in equal numbers if homologous centromeres are equally likely to segregate from the quadrivalent in alternate or adjacent modes. In addition, 4B:4W asci are produced with a frequency characteristic of each reciprocal translocation. Information on ascospore-abortion patterns in Neurospora crassa has come predominantly from unordered ascospore octads ejected from the perithecium. Unordered asci of the 4B:4W type were initially presumed to originate by interstitial crossing over in a centromere-breakpoint interval and their frequency was used as a predictor of centromere locations. However, 4B:4W asci can result not only from interstitial crossing over but also from nondisjunction of centromeres at the first meiotic division, which leads to 3:1 segregation. Ordered linear 4B:4W asci retain the sequence information necessary for distinguishing one mode of origin from the other but unordered asci do not. Crossing over results in one abortive duplication–deficiency ascospore pair in each opposite half of a linear ascus, while 3:1 segregation places both abortive ascospore pairs together, either in the distal half or the basal half of the ascus. In the present study, perithecia were opened and intact linear asci were examined in crosses heterozygous for a varied sample of translocations. Three-to-one segregation rather than interstitial crossing over is apparently the main cause of 4B:4W asci when breakpoints are near centromeres, whereas crossing over is responsible for most or all 4B:4W asci when breakpoints are far-distal. Three-to-one segregation does not impair the usefulness of ejected unordered asci for detecting chromosome rearrangements. Ejected octads are superior to ordered linear asci for distinguishing one type of rearrangement from another, because ascus ejection from the perithecium does not occur until viable ascospores are fully pigmented, enabling true 0B:8W asci to be distinguished from those with eight immature ascospores.Key words: ascospore abortion, ascus analysis, Neurospora, nondisjunction, reciprocal translocation, three-to-one segregation.

scholarly journals Memoirs: The Male Meiotic Phase in Two Genera of Marsupials (Macropus and Petauroides)

1923 ◽  
Vol s2-67 (266) ◽  
pp. 183-202
Author(s):  
W. E. AGAR
Keyword(s):  
Chromosome Number ◽  
Sex Chromosomes ◽  
Meiotic Division ◽  
Ovarian Follicle ◽  
The Other ◽  
Pachytene Stage ◽  
Follicle Cells ◽  
Crossing Over ◽  
Early Pachytene ◽  
Spermatogonial Metaphase

Macropus ualabatus has twelve chromosomes, namely 10 + XY in the male and 10 + XX in the female. In Petauroides the number is almost certainly twenty-two, the male being of the formula 20 + XY. No female counts were obtained for this animal. In the male Macropus Xis generally attached to one of the autosomes in spermatogonial mitoses. Y, which is exceedingly minute, is free. During the pachytene stage, while the autosomes are still elongated, X and Y condense into a bivalent. In the first meiotic division this bivalent is attached to an autosome. As a result of the first meiotic division the usual two classes of secondary spermatocytes are formed one with X and the other with Y. In the second meiotic division, those with X show only five separate chromosomes, showing that X, as usual, is fused with an autosome. The other class of second divisions shows five autosomes and the minute Y. In the female Macropus the sex chromosomes were never found free from the autosomes in the ovarian follicle cells, which therefore show only ten separate chromosomes. In Petauroides the sex chromosomes cannot be distinguished with certainty from the autosomes. An unequal pair of small chromosomes usually situated in the centre of the spermatogonial metaphase plates probably, however, are X and Y. Early pachytene nuclei show two compact bodies which unite into one, presumably the sex bivalent. The second reduction of the chromosome number to onequarter of the diploid total in the second meiotic division, which has been described for several species of birds and mammals, does not take place either in Macropus or Petauroides. Chromomeres are very prominent in Petauroides in the zygotene and diplotene stages. Probably in Macropus, and more convincingly in Petauroides, the cytological conditions to permit of ‘crossing over’ are present in the male. The plasmosome which appears in the pachytene stage is probably formed from the plastin or linin basis of the contracting sex chromosomes.

scholarly journals THE MANIFESTATION OF CHROMOSOME REARRANGEMENTS IN UNORDERED ASCI OF NEUROSPORA

Genetics ◽  
1974 ◽  
Vol 77 (3) ◽  
pp. 459-489
Author(s):  
David D Perkins
Keyword(s):  
Reciprocal Translocation ◽  
Chromosome Aberrations ◽  
Visual Inspection ◽  
Break Point ◽  
Crossing Over ◽  
Reciprocal Translocations ◽  
Analytical Technique ◽  
Large Numbers ◽  
Pericentric Inversions ◽  
Break Points

ABSTRACT Rapid, effective techniques have been developed for detecting and characterizing chromosome aberrations in Neurospora by visual inspection of ascospores and asci. Rearrangements that are detectable by the presence of deficient, nonblack ascospores in test crosses make up 5 to 10% of survivors after UV doses giving 10-55% survival. Over 135 rearrangements have been diagnosed by classifying unordered asci according to numbers of defective spores. (These include 15 originally identified or analyzed by other workers.) About 100 reciprocal translocations (RT's) have been confirmed and mapped genetically, involving all combinations of the seven chromosomes. Thirty-three other rearrangements generate viable nontandem duplications in meiosis. These consist of insertional translocations (IT's) (15 confirmed), and of rearrangements that involve a chromosome tip (10 translocations and 3 pericentric inversions). No inversion has been found that does not include the centromere. A reciprocal translocation was found within one population in nature. When pairs of RT's that involve the same two chromosome arms were intercrossed, viable duplications were produced if the breakpoints overlapped in such a way that pairing resembled that of insertional translocations (27 combinations).—The rapid analytical technique depends on the following. Deficiency ascospores are usually nonblack (W: "white") and inviable, while nondeficient ascospores, even those that include duplications, are black (B) and viable. Thus RT's typically produce 50% black spores, and IT's 75% black. Asci are shot spontaneously from ripe perithecia, and can be collected in large numbers as groups of eight ascospores representing unordered tetrads, which fall into five classes: 8B:0W; 6B:2W, 4B:4W, 2B:6B, 0B:8W. In isosequential crosses, 90-95% of tetrads are 8:0. When a rearrangement is heterozygous, the frequencies of tetrad classes are diagnostic of the type of rearrangement, and provide information also on the positions of break points. With RT's, 8:0 (alternate centromere segregation) = 0:8 (adjacent-1), 4:4's require interstitial crossing over in a centromere-break point interval, and no 6:2's or 2:6's are expected. With IT's, duplications are viable, 8:0 = 4:4, 6:2's are from interstitial crossing over, 0:8's or 2:6's are rare. Tetrads from RT's that involve a chromosome tip resemble those from IT's, as do tetrads from intercrosses between partially overlapping RT's that involve identical chromosome arms.—Because viable duplications and other aneuploid derivatives regularly occur among the offspring of rearrangements such as insertional translocations, care must be taken in selecting stocks, and original strains should be kept for reference.

scholarly journals Two types of sites required for meiotic chromosome pairing in Caenorhabditis elegans.

Genetics ◽  
1993 ◽  
Vol 134 (3) ◽  
pp. 749-768 ◽  
Author(s):  
K S McKim ◽  
K Peters ◽  
A M Rose
Keyword(s):  
Caenorhabditis Elegans ◽  
Meiotic Chromosome ◽  
Chromosome Rearrangement ◽  
The Other ◽  
Crossing Over ◽  
Homologous Chromosomes ◽  
Associated Sequences ◽  
Suppressed Recombination ◽  
The Right ◽  
Chromosome I

Abstract Previous studies have shown that isolated portions of Caenorhabditis elegans chromosomes are not equally capable of meiotic exchange. These results led to the proposal that a homolog recognition region (HRR), defined as the region containing those sequences enabling homologous chromosomes to pair and recombine, is localized near one end of each chromosome. Using translocations and duplications we have localized the chromosome I HRR to the right end. Whereas the other half of chromosome I did not confer any ability for homologs to pair and recombine, deficiencies in this region dominantly suppressed recombination to the middle of the chromosome. These deletions may have disrupted pairing mechanisms that are secondary to and require an HRR. Thus, the processes of pairing and recombination appear to utilize at least two chromosomal elements, the HRR and other pairing sites. For example, terminal sequences from other chromosomes increase the ability of free duplications to recombine with their normal homologs, suggesting that telomere-associated sequences, homologous or nonhomologous, play a role in facilitating meiotic exchange. Recombination can also initiate at internal sites separated from the HRR by chromosome rearrangement, such as deletions of the unc-54 region of chromosome I. When crossing over was suppressed in a region of chromosome I, compensatory increases were observed in other regions. Thus, the presence of the HRR enabled recombination to occur but did not determine the distribution of the crossover events. It seems most likely that there are multiple initiation sites for recombination once homolog recognition has been achieved.

pLoc_bal-mEuk: Predict Subcellular Localization of Eukaryotic Proteins by General PseAAC and Quasi-balancing Training Dataset

2019 ◽  
Vol 15 (5) ◽  
pp. 472-485 ◽  
Author(s):  
Kuo-Chen Chou ◽  
Xiang Cheng ◽  
Xuan Xiao
Keyword(s):  
Drug Development ◽  
Subcellular Localization ◽  
Basic Research ◽  
The Other ◽  
Training Dataset ◽  
Sequence Information ◽  
Eukaryotic Proteins ◽  
Validation Tests ◽  
User Friendly ◽  
Better Than

<P>Background/Objective: Information of protein subcellular localization is crucially important for both basic research and drug development. With the explosive growth of protein sequences discovered in the post-genomic age, it is highly demanded to develop powerful bioinformatics tools for timely and effectively identifying their subcellular localization purely based on the sequence information alone. Recently, a predictor called “pLoc-mEuk” was developed for identifying the subcellular localization of eukaryotic proteins. Its performance is overwhelmingly better than that of the other predictors for the same purpose, particularly in dealing with multi-label systems where many proteins, called “multiplex proteins”, may simultaneously occur in two or more subcellular locations. Although it is indeed a very powerful predictor, more efforts are definitely needed to further improve it. This is because pLoc-mEuk was trained by an extremely skewed dataset where some subset was about 200 times the size of the other subsets. Accordingly, it cannot avoid the biased consequence caused by such an uneven training dataset. </P><P> Methods: To alleviate such bias, we have developed a new predictor called pLoc_bal-mEuk by quasi-balancing the training dataset. Cross-validation tests on exactly the same experimentconfirmed dataset have indicated that the proposed new predictor is remarkably superior to pLocmEuk, the existing state-of-the-art predictor in identifying the subcellular localization of eukaryotic proteins. It has not escaped our notice that the quasi-balancing treatment can also be used to deal with many other biological systems. </P><P> Results: To maximize the convenience for most experimental scientists, a user-friendly web-server for the new predictor has been established at http://www.jci-bioinfo.cn/pLoc_bal-mEuk/. </P><P> Conclusion: It is anticipated that the pLoc_bal-Euk predictor holds very high potential to become a useful high throughput tool in identifying the subcellular localization of eukaryotic proteins, particularly for finding multi-target drugs that is currently a very hot trend trend in drug development.</P>

scholarly journals MITOTIC CROSSING OVER AND NONDISJUNCTION IN TRANSLOCATION HETEROZYGOTES OF ASPERGILLUS

Genetics ◽  
1976 ◽  
Vol 82 (4) ◽  
pp. 605-627
Author(s):  
Etta Käfer
Keyword(s):  
Selective Advantage ◽  
The Other ◽  
Translocation Chromosome ◽  
Crossing Over ◽  
Selective Marker ◽  
Reciprocal Translocations ◽  
Poor Growth ◽  
Different Types ◽  
Diploid Genotype ◽  
One Step

ABSTRACT To analyze mitotic recombination in translocation heterozygotes of A. nidulans two sets of well-marked diploids were constructed, homo- or heterozygous for the reciprocal translocations T1(IL;VIIR) or T2(IL;VIIIR) and heterozygous for selective markers on IL. It was found that from all translocation heterozygotes some of the expected mitotic crossover types could be selected. Such crossovers are monosomic for one translocated segment and trisomic for the other and recovery depends on the relative viabilities of these unbalanced types. The obtained segregants show characteristically reduced growth rates and conidiation dependent on sizes and types of mono- and trisomic segments, and all spontaneously produce normal diploid sectors. Such secondary diploid types either arose in one step of compensating crossing over in the other involved arm, or—more conspicuously—in two steps of nondisjunction via a trisomic intermediate.—In both of the analyzed translocations the segments translocated to IL were extremely long, while those translocated from IL were relatively short. The break in I for T1(I;VII) was located distal to the main selective marker in IL, while that of T2(I;VIII) had been mapped proximal but closely linked to it. Therefore, as expected, the selected primary crossover from the two diploids with T2(I;VIII) in coupling or in repulsion to the selective marker, showed the same chromosomal imbalance and poor growth. These could however be distinguished visually because they spontaneously produced different trisomic intermediates in the next step, in accordance with the different arrangement of the aneuploid segments. On the other hand, from diploids heterozygous for T1(I;VII) mitotic crossovers could only be selected when the selective markers were in coupling with the translocation; these crossovers were relatively well-growing and produced frequent secondary segregants of the expected trisomic, 2n+VII, type. For both translocations it was impossible to recover the reciprocal crossover types (which would be trisomic for the distal segments of I and monosomic for most of groups VII or VIII) presumably because these were too inviable to form conidia.—In addition to the selected segregants of expected types a variety of unexpected ones were isolated. The conditions of selection used favour visual detection of aneuploid types, even if these produce only a few conidial heads and are not at a selective advantage. For T2(I;VIII) these "non-selected" unbalanced segregants were mainly "reciprocal" crossovers of the same phenotype and imbalance as the selected ones. For T1(I;VII) two quite different types were obtained, both possibly originating with loss of the small VII-Itranslocation chromosome. One was isolated when the selective marker in repulsion to T1(I;VII) was used and, without being homo- or hemizygous for the selective marker, it produced stable sectors homozygous for this marker. The other was obtained from both coupling and repulsion diploids and showed a near-diploid genotype; it produced practically only haploid stable sectors of the type expected from monosomics, 2n-1 for the short translocation chromosome.

scholarly journals Evidence for Two Regions in the Mouse t Complex Controlling Transmission Ratios

1981 ◽  
Vol 38 (3) ◽  
pp. 315-325 ◽  
Author(s):  
Józefa Styrna ◽  
Jan Klein
Keyword(s):  
Lethal Factor ◽  
Compound Heterozygote ◽  
The Other ◽  
Transmission Ratio ◽  
Crossing Over ◽  
Normal Length ◽  
T Complex ◽  
Segregation Distorter ◽  
Haplotype A ◽  
Made In

SUMMARYFour new t haplotypes, tTu1 through tTu4, are described, three of them derived from the tw12tf haplotype and one (tTu4) from the tw2 haplotype. The tTu1 and tTu4 haplotypes cause taillessness in T/tTu1 or T/tTu4 heterozygotes, lack the lethality factor, weakly suppress recombination in the T−H−2 interval, and are transmitted to offspring from tTu/ + males at nearly Mendelian ratios. The tTu3 haplotype resembles tTu1 and tTu4 except for the fact that the T/tTu3 heterozygotes have normal-length tails. The tTu2 haplotype probably carries the lethal factor of tTu12tf, suppresses crossing-over in the T-H-2 and tf-H-2 intervals, and displays a slightly subnormal transmission ratio. In the compound heterozygote tTu1/tTu2, the male transmission ratio of the tTu1 chromosome is close to that of the original tTu12tf haplotype. A similar effect is observed in the tTu3/tTu2 heterozygote. This observation is interpreted as evidence for two regions within the t complex controlling the male transmission ratios. One of the regions is close to the tail-modifying region, the other is close to the lethality factor. Our findings parallel closely those made in the segregation distorter system in Drosophila.

Structural hybridity and supernumerary chromosomes in a diploid Tradescantia hirsuticaulis

1975 ◽  
Vol 53 (5) ◽  
pp. 456-465 ◽  
Author(s):  
C. C. Chinnappa
Keyword(s):  
Reciprocal Translocation ◽  
Cytological Study ◽  
B Chromosomes ◽  
The Other ◽  
Meiotic Pairing ◽  
Structural Hybridity ◽  
Supernumerary Chromosomes

Cytological study of a diploid (2n = 12) population of Tradescantia hirsuticaulis Small from Stone Mountain, Georgia, revealed striking variation in four plants growing in a cluster, indicating that they constitute different genotypes. The occurrence of B chromosomes, fragments, and aneusomaty in the plants is associated with structural hybridity in the chromosomes. Two plants were homozygotes with simple meiotic pairing, one was heterozygous for a reciprocal translocation, and the other was a heterozygote for two interchanges as well as for inversions. The behavior and the origin of B chromosomes, fragments, and structural hybridity are discussed.

Ascospore abortion in crosses of Cochliobolus heterostrophus heterozygous for the virulence locus Tox1

Genome ◽  
1988 ◽  
Vol 30 (1) ◽  
pp. 12-18 ◽  
Author(s):  
Charlotte R. Bronson
Keyword(s):  
Key Words ◽  
Reciprocal Translocation ◽  
High Frequency ◽  
Chromosome Rearrangement ◽  
Cochliobolus Heterostrophus ◽  
Bipolaris Maydis ◽  
Field Isolates

Crosses heterozygous for the virulence locus Tox1 show a high frequency of nonrandom ascospore abortion, in addition to a high frequency of random abortion seen in homozygous crosses. In crosses among closely related laboratory strains, the frequency of asci with eight mature, viable spores dropped from 35–47% of asci with mature spores in crosses homozygous for Tox1 to 3–17% in heterozygous crosses. Segregation for alternate alleles of Tox1 was 2:2 in 98% of asci with four viable spores. Patterns of abortion in crosses involving field isolates were similar to the patterns in crosses among laboratory strains. No recombinants between Tox1 and the abortion-inducing factor were detected among 112 progeny of laboratory strains. The results suggest that race T (TOX1) and race O (tox1) strains of C. heterostrophus differ by a chromosome rearrangement, possibly a reciprocal translocation, with a breakpoint at or near Tox1.Key words: fertility, T-toxin, Cochliobolus heterostrophus, Helminthosporium maydis, Bipolaris maydis, Drechslera maydis, chromosome rearrangement, reciprocal translocation.

Identification of two species of alpha motoneurons in cat's plantaris pool

1977 ◽  
Vol 40 (1) ◽  
pp. 16-25 ◽  
Author(s):  
D. A. Harris ◽  
E. Henneman
Keyword(s):  
Visual Inspection ◽  
Repetitive Stimulation ◽  
Ventral Root ◽  
Statistical Analyses ◽  
The Other ◽  
Small Samples ◽  
The Relationship ◽  
Decerebrate Cats ◽  
Two Populations ◽  
Stimulation Of

1. Single units of the plantaris pool were isolated in ventral root filaments of decerebrate cats and their critical firing levels (CFLs) were determined. Motoneurons of similar size, as judged by their CFLs and other criteria, were compared in firing rate (FR) during repetitive stimulation of the plantaris nerve. 2. Such units either differed very little or quite widely, suggesting that they were sampled randomly from two populations, one firing rapidly, the other slowly. The relationship between the two rates remained approximately constant, regardless of the intensity or rate of input the units received, as long as both of them discharged rhythmically. 3. In single experiments 10-15 of the smallest units in the pool (all with CFLs in the 0-8% range) were isolated and compared. Statistical analyses and visual inspection of these small samples again suggested the existence of two species of motoneurons. 4. Statistical analyses also indicated that the FRs of units in single experiments were not sampled from any one of a variety of parametric, single-modal distributions. This suggests that the data were sampled from a distribution having more than one mode, indicating the existence of separate populations or species of motoneurons among the small units of the pool (0-8% range of CFL). 5. Pooling of the normalized data from different experiments revealed a bimodal histogram, reinforcing the conclusion that there are two species of small alpha motoneurons in the plantaris pool.

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