Elimination of multivalents during meiotic prophase in Scilla autumnalis. I. Diploid and triploid

Genome ◽  
1988 ◽  
Vol 30 (6) ◽  
pp. 930-939 ◽  
Author(s):  
J. White ◽  
G. Jenkins ◽  
J. S. Parker
Keyword(s):  
Meiotic Prophase ◽  
Three Dimensional ◽  
Low Frequency ◽  
Chiasma Formation ◽  
Root Tip ◽  
Synaptonemal Complexes ◽  
Dimensional Reconstruction ◽  
Scilla Autumnalis ◽  
Surface Spreading ◽  
Pairing Behaviour

The ultrastructure and pairing behaviour of the chromosomes of two diploid cytotypes and a triploid of Scilla autumnalis were investigated using the techniques of three-dimensional reconstruction from serial electron micrographs and whole-mount surface spreading of synaptonemal complexes. The diploids, designated AA and B7B7, have karyotypes that are virtually identical in appearance at mitotic metaphase but differ in length by 47% and in DNA content by 66%. All the chromosomes were identified during meiotic prophase in both diploids, enabling construction of accurate karyotypes, which were the same as those derived from root tip metaphases. Chromosome pairing was largely regular with very few structural chromosome rearrangements. These two observations permitted confident interpretations of multivalent configurations observed in polyploids containing multiples of the A and B7 genomes. In the triploid (AB7B7) during meiotic prophase lateral components are associated in groups of three, either as trivalents with several exchanges of pairing partners, or as bivalents and univalents in close alignment. The overall difference in length between A and B7 chromosomes is close to expected, but varies to some degree depending on the extent of pairing between the two chromosome types. Most of the synaptonemal complexes between A and B7 homoeologues are ineffective in terms of chiasma formation, as revealed by the low frequency of multivalents and heteromorphic bivalents at metaphase I. In other words, there is an elimination of multivalents during meiotic prophase in the triploid.Key words: Scilla autumnalis, synaptonemal complex, multivalents, elimination.

Presence of abnormal synaptonemal complexes in heterothallic species of Neurospora

Genome ◽  
1988 ◽  
Vol 30 (5) ◽  
pp. 697-709 ◽  
Author(s):  
Maja Bojko
Keyword(s):  
Synaptonemal Complex ◽  
Meiotic Prophase ◽  
Low Frequency ◽  
Chiasma Formation ◽  
Lateral Component ◽  
Late Pachytene ◽  
Synaptonemal Complexes ◽  
Neurospora Intermedia ◽  
Heterothallic Species ◽  
Type Strains

Synaptonemal complex abnormalities are frequent in reconstructed meiotic prophase nuclei of Neurospora crassa and Neurospora intermedia. Three kinds of synaptonemal complex anomalies were seen: lateral component splits, lateral component junctions, and multiple complexes. The anomalies apparently are formed during or after the pairing process, as they were not seen in the largely unpaired early zygotene chromosomes. Their presence at all the other substages from mid-zygotene to late pachytene indicates that they are not eliminated before the synaptonemal complex decomposes at diplotene. Abnormal synaptonemal complexes were seen in all 19 crosses of N. crassa and N. intermedia that were examined, including matings between standard laboratory strains, inversions, Spore killers, and strains collected from nature. The frequency of affected nuclei and degree of abnormality within a nucleus varied in different matings. No abnormalities were present in the homothallic species Neurospora africana and Neurospora terricola. Structural chromosome aberrations, introgression, and heterozygosity have been eliminated as causes for pairing disorder. The abnormal synaptonemal complexes seemingly do not interfere with normal ascus development and ascospore formation. The affected nuclei are not aborted during meiotic prophase, nor are they eliminated by abortion of mature asci. The abnormal meiocytes do not lead to aneuploidy, as judged by the low frequency of white ascospores in crosses between wild type strains that have many abnormalities. Thus, the abnormal synatonemal complexes do not appear to prevent chiasma formation between homologues.Key words: Neurospora, meiosis, synaptonemal complex.

Elimination of multivalents during meiotic prophase in Scilla autumnalis. II. Tetraploid

Genome ◽  
1988 ◽  
Vol 30 (6) ◽  
pp. 940-946 ◽  
Author(s):  
G. Jenkins ◽  
J. White ◽  
J. S. Parker
Keyword(s):  
Synaptonemal Complex ◽  
Meiotic Prophase ◽  
Chiasma Formation ◽  
Serial Sections ◽  
Genomic Constitution ◽  
Homologous Chromosomes ◽  
Multivalent Formation ◽  
Whole Mount ◽  
Scilla Autumnalis ◽  
Pairing Behaviour

The pairing behaviour of chromosomes during meiotic prophase in two Scilla autumnalis tetraploids was investigated by observing synaptonemal complexes from serial sections and whole-mount surface spreads. In one of the tetraploids with the genomic constitution AAB7B7 pairing at first metaphase of meiosis is restricted to homologous chromosomes and only bivalents appear. In the second tetraploid, AB7B7B7, some multivalents are found at first metaphase, but most of the configurations are bivalent. The bivalents, however, result from chiasma formation between homoeologous as well as homologous chromosomes. Both tetraploids show extensive multivalent formation at zygotene. The transformation of these multivalents to bivalents is described and interpreted in the two tetraploid forms.Key words: Scilla autumnalis, synaptonemal complex, multivalents, elimination, polyploids.

The synaptonemal complexes of Achlya recurva (Oomycetes): karyotype analysis and three-dimensional reconstruction of pachytene nuclei in antheridia and oogonia

1991 ◽  
Vol 69 (6) ◽  
pp. 1384-1395 ◽  
Author(s):  
Hobart R. Williamson ◽  
Pesach Ben Yitzchak
Keyword(s):  
Synaptonemal Complex ◽  
Organizer Region ◽  
Nucleolar Organizer Region ◽  
Nucleolus Organizer Region ◽  
Three Dimensional ◽  
Central Element ◽  
Three Dimensional Reconstruction ◽  
Synaptonemal Complexes ◽  
Sequence Of Events ◽  
Dimensional Reconstruction

Fifteen synaptonemal complexes, as determined by three-dimensional reconstruction of serial, ultrathin sections, were present within both antheridial and oogonial zygotene and pachytene nuclei of the oomyceteous fungus Achlya recurva, thus n = 15. The present study represents the first complete reconstruction of synaptonemal complexes in the genus Achlya. The occurrence of both zygonema and pachynema was simultaneous in antheridia and oogonia. Pachytene nuclei of antheridia and oogonia are small, 13 μm3 in volume, and the average length of the synaptonemal complexes ranged from 1.9 to 4.4 μm. Lateral elements at zygotene ranged from 1.2 to 4.7 μm. Both ends of each synaptonemal complex were attached randomly to the nuclear envelope, so a bouquet formation was not observed at pachytene. In A. recurva, the dimensions of the synaptonemal complex were as follows: overall width = 270 nm; the lateral elements = 75 nm each in width and the central region = 120 nm. There was no central element and associated transverse filaments, which may be associated with development of alternative reproductive strategies other than amphimixis, as in nematodes. Of the 15 synaptonemal complexes present, only the one carrying the nucleolus organizer region could be clearly identified from one nucleus to the next. The nucleolar organizer region was on the average 0.75 μm from the telomere in both zygotene and pachytene nuclei. There were an average of three recombination nodules in each nucleus. Synaptonemal complexes have been reported in over 80 different species of fungi and related protista. Karyotypic evolution in the oomycetes and fungi may be the result of poly-ploidization, followed by cytogenetic diversification involving aneuploidy and differing degrees of polyploidy. Such a sequence of events could explain the apparent polyphyletic formation of this group. Key words: karyotype, Oomycetes, pachytene, synaptonemal complexes, three-dimensional reconstruction.

Synapsis in grasshopper bivalents heterozygous for centric shifts

Genome ◽  
1995 ◽  
Vol 38 (3) ◽  
pp. 616-622 ◽  
Author(s):  
A. L. del Cerro ◽  
J. L. Santos
Keyword(s):  
Chiasma Formation ◽  
The Other ◽  
Homologous Chromosomes ◽  
Synaptonemal Complexes ◽  
Chiasma Distribution ◽  
Centric Shift ◽  
Heterochromatin Polymorphism ◽  
Pachytene Spermatocytes ◽  
Surface Spread ◽  
Surface Spreading

Analysis of surface-spread synaptonemal complexes of zygotene and pachytene spermatocytes was carried out on centric-shift heterozygotes of grasshoppers. These rearrangements affected the M7 chromosome in Chorthippus vagans and the M6 and S8 chromosomes in Chorthippus apricarius. The shifts in the latter two chromosomes were also associated with C-heterochromatin variations between homologous chromosomes. Rearranged chromosomes proceeded directly to heterosynapsis without an apparent intervening homosynaptic phase in M7 bivalents of Ch. vagans and M6 bivalents of Ch. apricarius. In the latter case, axial equalization of the heterochromatin polymorphism was also achieved. On the other hand, asynapsis of the intercentromeric regions throughout pachytene was the rule in the centric shift involving the S8 chromosome of Ch. apricarius. In the three cases analysed, the production of unbalanced gametes in the heterozygotes is precluded either by the lack of chiasma formation in heterosynapsed rearranged segments or by the lack of pairing between such segments. Chiasmata were limited to the homologous regions of the heteromorphic bivalents.Key words: synapsis, surface spreading, centric shift, chiasma distribution, meiosis.

The assembly of the synaptinemal complex

1977 ◽  
Vol 277 (955) ◽  
pp. 235-243 ◽  
Keyword(s):  
Central Region ◽  
Three Dimensional ◽  
Chiasma Formation ◽  
Central Component ◽  
Lateral Component ◽  
Late Zygotene ◽  
Homologous Chromosomes ◽  
Synaptinemal Complex ◽  
Central Regions ◽  
Dimensional Reconstruction

The assembly of the synaptinemal complex in the ascomycete Neottiella was studied by three-dimensional reconstruction of a late zygotene nucleus. A single banded lateral component is formed between the two sister chromatids of each homologous chromosome prior to their pairing. The central regions are pre-assembled in organized form in folds of the granular part of the nucleolus and then converted into an amorphous transport form. The latter appears to move through the nucleoplasm to sites between the lateral components of synapsing homologous chromosomes. The central region material is reorganized into blocks with a recognizable central component and attached to one lateral component. The last step in the completion of the synaptinemal complex is the association of the free surface of the organized central region with the corresponding segment of the homologous lateral component. The findings are discussed in relation to mechanisms of chromosome pairing and chiasma formation.

Denoising and 3D Reconstruction of CT Images in Extracted Tooth via Wavelet and Bilateral Filtering

2018 ◽  
Vol 32 (05) ◽  
pp. 1854010 ◽  
Author(s):  
Cuizhen Wang ◽  
Zhenxue Chen ◽  
Yan Wang ◽  
Zhifeng Wang
Keyword(s):  
3D Reconstruction ◽  
Signal To Noise Ratio ◽  
Three Dimensional ◽  
Similarity Index ◽  
Low Frequency ◽  
Structural Similarity ◽  
Bilateral Filtering ◽  
Denoising Method ◽  
Dimensional Reconstruction ◽  
Index Measure

Three-dimensional reconstruction of teeth plays an important role in the operation of living dental implants. However, the tissue around teeth and the noise generated in the process of image acquisition bring a serious impact on the reconstruction results, which must be reduced or eliminated. Combined with the advantages of wavelet transform and bilateral filtering, this paper proposes an image denoising method based on the above methods. The method proposed in this paper not only removes the noise but also preserves the image edge details. The noise in high frequency subbands is denoised using a locally adaptive thresholding and the noise in low frequency subbands is filtered by the bilateral filtering. Peak signal-to-noise ratio (PSNR), structural similarity index measure (SSIM) and 3D reconstruction using the iso-surface extraction method are used to evaluate the denoising effect. The experimental results show that the proposed method is better than the wavelet denoising and bilateral filtering, and the reconstruction results meet the requirements of clinical diagnosis.

The Synaptonemal Complex and the Achiasmatic Condition

1973 ◽  
Vol 13 (1) ◽  
pp. 83-95 ◽  
Author(s):  
S. STACK
Keyword(s):  
Light Microscopy ◽  
Microscopic Examination ◽  
Three Dimensional ◽  
Electron Microscopic Examination ◽  
Chiasma Formation ◽  
Crossing Over ◽  
Electron Microscopic ◽  
Synaptonemal Complexes ◽  
Chromosome Arrangements ◽  
Onion Species

The onion species Allium amplectans includes both a triploid and a tetraploid variety. By light microscopy both varieties appear to have normal synapsis during pachytene of meiosis. However, the triploid does not form chiasmata and exhibits almost total asynapsis following pachytene. The tetraploid forms at least one chiasma per homologue and retains pairing through metaphase I. Electron-microscopic examination of pachytene nuclei in these 2 varieties reveals apparently identical synaptonemal complexes. Three-dimensional reconstructions of chromosome arrangements in triploid pachytene nuclei confirm that synapsis is as complete as could be expected in an autotriploid. These observations give firm support to the hypothesis that the presence of apparently structurally normal synaptonemal complexes is not a sufficient prerequisite to ensure chiasma formation. It is suggested that a faulty or missing endonuclease which is normally involved in crossing over is responsible for the achiasmatic condition in triploid A. amplectans.

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