NON-RANDOM CHROMOSOME ASSOCIATIONS AT DIPLOTENE AND DIAKINESIS IN A TETRAPLOID CLONE OF VACCINIUM AUSTRALE SMALL

1971 ◽  
Vol 13 (2) ◽  
pp. 270-276 ◽  
Author(s):  
G. Jelenkovic ◽  
E. Harrington
Keyword(s):  
Meiotic Division ◽  
Great Majority ◽  
Late Prophase ◽  
Multivalent Formation ◽  
Chromosome Associations ◽  
Tetraploid Genotype

In a cultivated tetraploid genotype (2n=4x=48) of Vaccinium australe Small the chromosome associations at late prophase of the first meiotic division and the separation of the chromosomes at anaphase I and anaphase II were investigated.Of the 223 PMC's analyzed one quarter of them displayed only bivalent associations; the remaining displayed both bivalent and quadrivalent associations. In about 3% of the PMC's, hexavalents were observed. No univalents, trivalents or pentavalents were found. The non-randomness of the chromosome associations is interpreted as resulting from obligatory pairing and localized distal chiasma.In spite of multivalent formation, in 115 PMC's studied, separation of the chromosomes at anaphase I is regular and in 95 daughter nuclei 24 chromosomes were counted. At anaphase II, the great majority of the nuclei revealed regular separation of the chromosomes and consequently numerically balanced gametes are produced.

CHROMOSOME ASSOCIATIONS IN THE FIRST MEIOTIC DIVISION IN THREE TETRAPLOID CLONES OF VACCINIUM CORYMBOSUM L

1970 ◽  
Vol 12 (2) ◽  
pp. 316-324 ◽  
Author(s):  
G. Jelenkovic ◽  
L. F. Hough
Keyword(s):  
Relaxation Process ◽  
Chromosome Pairing ◽  
Meiotic Division ◽  
Great Majority ◽  
Vaccinium Corymbosum ◽  
Early Prophase ◽  
Chromosome Associations

The analysis of chromosome pairing in three tetraploid cultivars of Vaccinium corymbosum L. revealed chat the great majority of bivalents were involved in pseudo-multivalent associations. The number of independent bivalents (not involved in formation of multivalents) increased from diakinesis to metaphase I.The pseudo-multivalents at diakinesis and at MI are the consequence of incomplete relaxation of the synizetic knot, a dense chromatic mass observed in early prophase. Factors that might affect the relaxation process are discussed.

Unorthodox male meiosis in Trichosia pubescens (Sciaridae). Chromosome elimination involves polar organelle degeneration and monocentric spindles in first and second division

1994 ◽  
Vol 107 (1) ◽  
pp. 299-312 ◽  
Author(s):  
H. Fuge
Keyword(s):  
Meiotic Division ◽  
Metaphase Plate ◽  
Chromosome Elimination ◽  
Spindle Pole ◽  
Male Meiosis ◽  
Early Prophase ◽  
Late Prophase ◽  
Section Electron ◽  
The One ◽  
Polar Organelle

Male meiosis in Trichosia pubescens (Sciaridae) was investigated by means of serial section electron microscopy and immunofluorescence light microscopy. From earlier studies of another sciarid fly, Sciara coprophila (Phillips (1967) J. Cell. Biol. 33, 73–92), it is known that the spindle poles in sciarid spermatogonia are characterized by pairs of ‘giant centrioles’, ring-shaped organelles composed of large numbers of singlet microtubules. In the present study spermatocytes in early prophase of Trichosia were found to possess single giant centrioles at opposite sides of the nucleus. The obvious reduction in centriole number from the spermatogonial to the spermatocyte stage is suggested to be the result of a suppression of daughter centriole formation. In late prophase, a large aster is developed around the centriole at one pole. At the opposite pole no comparable aster is formed. Instead, a number of irregular centriolar components appear in this region, a process that is understood to be a degeneration of the polar organelle. The components of the degenerate pole migrate into a cytoplasmic protrusion (‘bud’), which later is also utilized for the elimination of paternal chromosomes. The existence of only one functional polar centre is the reason for the formation of a monopolar monocentric spindle in first meiotic division, which in turn is one of the prerequisites for the elimination of paternal chromosomes. While the set of maternal and L chromosomes orientates and probably moves towards the pole, paternal chromosomes seem to be unable to contact the pole, possibly due to an inactivation of their kinetochores. Retrograde (‘away from the pole’) chromosome motion not involving kinetochores is assumed. Eventually, paternal chromosomes move into the pole-distal bud and are eliminated by casting off, together with the components of the degenerate polar organelle. Chromosome elimination can be delayed until the second meiotic division. The spindle of the second meiotic division is bipolar and monocentric. One spindle pole is marked by the polar centre of first division. The opposite spindle apex is devoid of a polar centre. It is assumed that spindle bipolarity in the second division is induced by the amphi-orientated chromosomes themselves. The maternal and L chromosome set (except the non-disjunctional X chromosome, which is found near the polar centre) congress in a metaphase plate, divide and segregate. Of the two daughter nuclei resulting from the second meiotic division, the one containing the X chromatids is retained as the nucleus of the future spermatozoon. The other nucleus becomes again eliminated within a second cytoplasmic bud.

Cytogenetics of decaploid Agropyron elongatum (Elytrigia elongata) (2n = 70). I. Frequency of decavalent formation

Genome ◽  
1990 ◽  
Vol 33 (6) ◽  
pp. 811-817 ◽  
Author(s):  
Mikio Muramatsu
Keyword(s):  
High Frequency ◽  
Chromosome Association ◽  
Agropyron Elongatum ◽  
Homologous Chromosomes ◽  
Ring Shape ◽  
Meiotic Configuration ◽  
Multivalent Formation ◽  
A Cell ◽  
Chromosome Associations ◽  
Metaphase I

The multivalents that appeared in the decaploid strain of Agropyron elongatum (2n = 10x = 70), a relative of wheat, ranged from trivalent to decavalent. Few univalents occurred. The metaphase I chromosome association in 12 cells where all configurations could clearly be identified averaged 0.42 ring X + 0.17 chain X + 0.42 ring VIII + 0.17 branched VIII + 0.25 chain VIII + 0.17 chain VII + 1.17 ring VI + 0.33 branched VI + 0.5 chain VI + 1.67 ring IV + 0.42 branched IV + 0.58 chain IV + 0.08 branched III + 0.17 chain III + 12.58 ring II + 3.75 open II + 0.25 I. The occurrence of decavalents, up to two in one cell, and of a cell with five multivalents, each of which involved more than five chromosomes, and many multivalents of ring shape indicated that the strain is autodecaploid.The chromosome associations of each cell can be interpreted as seven groups of 10 homologous chromosomes. The high frequency of bivalents indicated a tendency toward reduced multivalent formation, for which an explanation is suggested.Key words: Agropyron elongatum, meiotic configuration, decaploid, multivalent.

scholarly journals Sex Chromosome Pairing Mediated by Euchromatic Homology in Drosophila Male Meiosis

Genetics ◽  
2020 ◽  
Vol 214 (3) ◽  
pp. 605-616 ◽  
Author(s):  
Christopher A. Hylton ◽  
Katie Hansen ◽  
Andrew Bourgeois ◽  
John E. Tomkiel Dean
Keyword(s):  
Sex Chromosome ◽  
Intergenic Spacer ◽  
Male Meiosis ◽  
Early Prophase ◽  
Dna Breaks ◽  
Late Prophase ◽  
Prophase I ◽  
Double Strand Dna Breaks ◽  
Chromosome Associations ◽  
Meiosis I

Diploid germline cells must undergo two consecutive meiotic divisions before differentiating as haploid sex cells. During meiosis I, homologs pair and remain conjoined until segregation at anaphase. Drosophila melanogaster spermatocytes are unique in that the canonical events of meiosis I including synaptonemal complex formation, double-strand DNA breaks, and chiasmata are absent. Sex chromosomes pair at intergenic spacer sequences within the ribosomal DNA (rDNA). Autosomes pair at numerous euchromatic homologies, but not at heterochromatin, suggesting that pairing may be limited to specific sequences. However, previous work generated from genetic segregation assays or observations of late prophase I/prometaphase I chromosome associations fail to differentiate pairing from maintenance of pairing (conjunction). Here, we separately examined the capability of X euchromatin to pair and conjoin using an rDNA-deficient X and a series of Dp(1;Y) chromosomes. Genetic assays showed that duplicated X euchromatin can substitute for endogenous rDNA pairing sites. Segregation was not proportional to homology length, and pairing could be mapped to nonoverlapping sequences within a single Dp(1;Y). Using fluorescence in situ hybridization to early prophase I spermatocytes, we showed that pairing occurred with high fidelity at all homologies tested. Pairing was unaffected by the presence of X rDNA, nor could it be explained by rDNA magnification. By comparing genetic and cytological data, we determined that centromere proximal pairings were best at segregation. Segregation was dependent on the conjunction protein Stromalin in Meiosis, while the autosomal-specific Teflon was dispensable. Overall, our results suggest that pairing may occur at all homologies, but there may be sequence or positional requirements for conjunction.

CHROMOSOME ASSOCIATIONS AT DIAKINESIS IN THE CULTIVATED STRAWBERRY

1971 ◽  
Vol 13 (2) ◽  
pp. 231-236 ◽  
Author(s):  
D. W. S. Mok ◽  
W. D. Evans
Keyword(s):  
Chromosome Pairing ◽  
Genetic Data ◽  
Cytological Evidence ◽  
Tetrasomic Inheritance ◽  
Secondary Pairing ◽  
Multivalent Formation ◽  
Chromosome Associations

The analysis of chromosome pairing in the cultivated strawberry revealed that multivalent formation occurs in each of the nine cultivars examined. Secondary pairing and a loose association of bivalents were also observed. The cytological evidence suggests that tetrasomic inheritance should be considered in the interpretation of genetic data.

CYTOLOGICAL DIPLOIDIZATION IN THE CULTIVATED OCTOPLOID STRAWBERRY FRAGARIA × ANANASSA

1976 ◽  
Vol 18 (4) ◽  
pp. 653-659 ◽  
Author(s):  
D. Byrne ◽  
G. Jelenkovic
Keyword(s):  
Chromosome Pairing ◽  
Fragaria Ananassa ◽  
Late Prophase ◽  
Multivalent Formation ◽  
Bivalent Association ◽  
Prophase Of Meiosis

Chromosome pairing during meiosis was studied in 9 cultivated genotypes and 32 seedlings produced by selfing several different genotypes of the octoploid strawberry Fragaria × ananassa Duch. (2n = 8x = 56). In all genotypes studied the chromosomes paired exclusively as bivalents indicating cytological diploidization. Meiotic studies of one of the S1 plants, which was completely sterile, revealed that the chromosomes were paired at pachytene but desynapsed during diplotene, so that very little bivalent association was observed in late prophase of meiosis. The pairing in the F. × ananassa × F. nubicola pentaploid hybrids showed an average of 11.6 bivalents per PMC and frequent multivalent formation. There is thus an indication of residual homology between the ancestral genomes of the octoploid strawberry.

Internal migration in Italy. Long-run analysis of push and pull factors across regions and macro-areas of the country.

2016 ◽  
Vol 13 (3) ◽  
pp. 443-454
Author(s):  
Piras Romano
Keyword(s):  
Gravity Model ◽  
Internal Migration ◽  
Empirical Studies ◽  
Great Majority ◽  
Pull Factors ◽  
Push And Pull Factors ◽  
Long Run ◽  
Italian Regions ◽  
Migration Flows ◽  
Push And Pull

The great majority of empirical studies on internal migration across Italian regions either ignores the long-run perspective of the phenomenon or do not consider push and pull factors separately. In addition, Centre-North to South flows, intra-South and intra-Centre-North migration have not been studied. We aim to fill this gap and tackle interregional migration flows from different geographical perspectives. We apply four panel data estimators with different statistical assumptions and show that long-run migration flows from the Mezzogiorno towards Centre-Northern regions are well explained by a gravity model in which per capita GDP, unemployment and population play a major role. On the contrary, migration flows from Centre-North to South has probably much to do with other social and demographic factors. Finally, intra Centre-North and intra South migration flows roughly obey to the gravity model, though not all explicative variables are relevant.

Phonologically conditioned allomorphy in the morphology of Surmiran (Rumantsch)

2008 ◽  
Vol 1 (2) ◽  
pp. 109-134 ◽  
Author(s):  
Stephen R. Anderson
Keyword(s):  
Optimality Theory ◽  
General Framework ◽  
Great Majority ◽  
Historical Change ◽  
Romance Languages ◽  
Morphological Properties ◽  
Entire System ◽  
Verbal System ◽  
Extended Sense ◽  
Phonological Rule

Alternations between allomorphs that are not directly related by phonological rule, but whose selection is governed by phonological properties of the environment, have attracted the sporadic attention of phonologists and morphologists. Such phenomena are commonly limited to rather small corners of a language's structure, however, and as a result have not been a major theoretical focus. This paper examines a set of alternations in Surmiran, a Swiss Rumantsch language, that have this character and that pervade the entire system of the language. It is shown that the alternations in question, best attested in the verbal system, are not conditioned by any coherent set of morphological properties (either straightforwardly or in the extended sense of ‘morphomes’ explored in other Romance languages by Maiden). These alternations are, however, straightforwardly aligned with the location of stress in words, and an analysis is proposed within the general framework of Optimality Theory to express this. The resulting system of phonologically conditioned allomorphy turns out to include the great majority of patterning which one might be tempted to treat as productive phonology, but which has been rendered opaque (and subsequently morphologized) as a result of the working of historical change.

Optimum Therapies for ST-Elevation Myocardial Infarction Managed with Primary Percutaneous Coronary Intervention

2012 ◽  
Vol 7 (2) ◽  
pp. 81
Author(s):  
Bruce R Brodie ◽  
Keyword(s):  
Myocardial Infarction ◽  
Percutaneous Coronary Intervention ◽  
Primary Percutaneous Coronary Intervention ◽  
Great Majority ◽  
Coronary Intervention ◽  
St Elevation Myocardial Infarction ◽  
Stent Deployment ◽  
Aspiration Thrombectomy ◽  
Percutaneous Coronary ◽  
St Elevation

This article reviews optimum therapies for the management of ST-elevation myocardial infarction (STEMI) with primary percutaneous coronary intervention (PCI). Optimum anti-thrombotic therapy includes aspirin, bivalirudin and the new anti-platelet agents prasugrel or ticagrelor. Stent thrombosis (ST) has been a major concern but can be reduced by achieving optimal stent deployment, use of prasugrel or ticagrelor, selective use of drug-eluting stents (DES) and use of new generation DES. Large thrombus burden is often associated poor outcomes. Patients with moderate to large thrombus should be managed with aspiration thrombectomy and patients with giant thrombus should be treated with glycoprotein IIb/IIIa inhibitors and may require rheolytic thrombectomy. The great majority of STEMI patients presenting at non-PCI hospitals can best be managed with transfer for primary PCI even with substantial delays. A small group of patients who present very early, who are at high clinical risk and have long delays to PCI, may best be treated with a pharmaco-invasive strategy.

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