scholarly journals AN ANALYSIS OF FREQUENCIES OF CHROMOSOME CONFIGURATIONS IN WHEAT AND WHEAT HYBRIDS

Genetics ◽  
1979 ◽  
Vol 91 (4) ◽  
pp. 755-767
Author(s):  
C J Driscoll ◽  
L M Bielig ◽  
N L Darvey
Keyword(s):  
Chiasma Formation ◽  
Homologous Chromosomes ◽  
Sequence Of Events ◽  
Chromosome 5B ◽  
Wheat Hybrids ◽  
Colchicine Application ◽  
Metaphase I

ABSTRACT Presynaptic association of homologous chromosomes is a prerequisite to the sequence of events that lead to chiasma formation. This association of homologous chromosomes, as entire units, occurs with probability a, and chiasma formation occurs independently in opposite chromosome arms with probability c. a and c have been estimated from frequencies of different chromosome configurations at metaphase I of euhexaploid wheat and several derived lines. In the euploid, a is essentially unity and c is of the order of 95%. All changes in the aneuploidy studied involved c rather than a, whereas the change induced by colchicine application primarily involved a.—Observed and expected frequencies of configurations were compared in wheat hybrids in which only homoeologues were present. The expected frequencies of configurations were estimated from the data, based on a being unity for entire groups of homoeologues and c being the probability of chiasma formation between random homoeologous arms. Observed and expected frequences of configurations were in general agreement; however, an excess of observed closed bivalents at the expense of multivalents is interpreted to mean that not all homoeologues are effectively associated in all cells.—In euhexaploid wheat, we suggest that homologues associate with almost certainty, whereas homoeologous pairs of chromosomes associate less efficiently. The aneuploidy examined in this study does not appear to affect the association of chromosomes, but rather the number of chiasmata that eventuate and, in the case of deficiency of chromosome 5B the distribution of chiasmata within homoelogues, perhaps by way of rendering sites for chiasma formation of homoelogues more similar.

Metaphase I pairing of deficient chromosomes and genetic mapping of deficiency breakpoints in common wheat

Genome ◽  
1991 ◽  
Vol 34 (4) ◽  
pp. 553-560 ◽  
Author(s):  
C. A. Curtis ◽  
A. J. Lukaszewski ◽  
M. Chrzastek
Keyword(s):  
Triticum Aestivum ◽  
Genetic Mapping ◽  
Chromosome Pairing ◽  
Triticum Aestivum L ◽  
Genetic Distances ◽  
Homologous Chromosomes ◽  
Transmission Rates ◽  
Chromosome 5B ◽  
Pairing Initiation ◽  
Metaphase I

Metaphase I pairing of deficient chromosomes was analyzed in a set of 'Chinese Spring' (CS) wheat (Triticum aestivum L. em. Thell.) plants with varying lengths of deficiencies in the long arm of chromosome 4A (6, 8, 11, 17, 23, 34, 36, 39, and 50% missing), the long arm of chromosome 5B (49% missing), and the long arm of chromosome 2B (33% missing). Pairing in homologous chromosomes between deficient and complete arms was greatly reduced even by small differences in arm length. In deficiency homozygotes and in an isochromosome derived from a deficient 4AL arm, pairing of the two deficient arms was high and approached that of two complete arms. In plants where deficient and complete arms competed for pairing partners, pairing was exclusively between arms of the same length. These results suggest that in wheat, pairing initiation sites are distributed throughout at least the distal halves of the arms and that the alignment of telomeres may be critical for pairing success. Genetic mapping of the deficiency breakpoints was confounded by misdivision of unpaired chromosomes and abnormal transmission rates. Genetic distances between centromeres and breakpoints appeared to be proportional to metaphase I pairing frequencies.Key words: bread wheat, deficiency, chromosome pairing competition, mapping, telomere, pairing initiation.

Chromosome pairing in the allotetraploid Aegilops biuncialis and a triploid intergeneric hybrid

Genome ◽  
1996 ◽  
Vol 39 (4) ◽  
pp. 664-670 ◽  
Author(s):  
N. Cuñado ◽  
S. Callejas ◽  
M. J. García ◽  
J. L Santos ◽  
A. Fernández
Keyword(s):  
Synaptonemal Complex ◽  
Chromosome Pairing ◽  
Complex Analysis ◽  
Intergeneric Hybrid ◽  
Chiasma Formation ◽  
Triploid Hybrid ◽  
Homologous Chromosomes ◽  
Prophase I ◽  
Surface Spread ◽  
Metaphase I

Chromosome pairing behaviour of the natural allotetraploid Aegilops biuncialis (genome UUMM) and a triploid hybrid Ae. biuncialis × Secale cereale (genome UMR) was analyzed by electron microscopy in surface-spread prophase I nuclei. Synaptonemal-complex analysis at zygotene and pachytene revealed that synapsis in the allotetraploid was mostly between homologous chromosomes, although a few quadrivalents were also formed. Only homologous bivalents were observed at metaphase I. In contrast, homoeologous and heterologous chromosome associations were common at prophase I and metaphase I of the triploid hybrid. It is concluded that the mechanism controlling bivalent formation in Ae. biuncialis acts mainly at zygotene by restricting pairing to homologous chromosomes, but also acts at pachytene by preventing chiasma formation in the homoeologous associations. In the hybrid the mechanism fails at both stages. Key words : Aegilops biuncialis, allotetraploid, intergeneric hybrid, pairing control, synaptonemal complex.

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.

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.

Analysis of synaptonemal complexes and chromosome pairing at metaphase I in the diploid intergeneric hybrid Lolium multiflorum × Festuca drymeja

Genome ◽  
1990 ◽  
Vol 33 (4) ◽  
pp. 465-471 ◽  
Author(s):  
Hum M. Thomas ◽  
W. G. Morgan
Keyword(s):  
Chromosome Pairing ◽  
Complex Analysis ◽  
Lolium Multiflorum ◽  
Intergeneric Hybrid ◽  
Chiasma Formation ◽  
Genotypic Effect ◽  
Synaptonemal Complexes ◽  
Dna Values ◽  
Synaptonemal Complex Analysis ◽  
Metaphase I

The synaptonemal complexes in the diploid hybrid Lolium multiflorum × Festuca drymeja were examined by the surface spreading technique, and chromosome pairing at metaphase I was analysed. Synaptonemal complex analysis revealed "illegitimate" pairing, including multivalents and foldback pairing. At metaphase I, most chiasmata were between chromosomes of the same genome, and again multivalents were found. It was concluded that most synaptonemal complexes resulted in chiasma formation. The effects of the large differences in DNA values of the two species and the possible genotypic effect of F. drymeja on chromosome pairing are discussed.Key words: Lolium-Festuca, synaptonemal complexes, nonhomologous pairing, DNA values.

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.

THE EFFECT OF COLCHICINE ON CHROMOSOME PAIRING

1977 ◽  
Vol 19 (2) ◽  
pp. 231-249 ◽  
Author(s):  
J. B. Thomas ◽  
P. J. Kaltsikes
Keyword(s):  
Aqueous Solution ◽  
Chromosome Pairing ◽  
Close Association ◽  
Tetraploid Wheat ◽  
Continuous Illumination ◽  
Hexaploid Triticale ◽  
Homologous Chromosomes ◽  
Wheat Hybrids ◽  
Bouquet Stage

Beginning at 120 hours prior to first metaphase of meiosis (MI) a 0.03% aqueous solution of colchicine was injected into the boot of pentaploid (hexaploid triticale × tetraploid wheat) hybrids developing at 20 °C ± 1° under continuous illumination. Colchicine applied 40 h or less prior to MI had no effect on chromosome pairing, while its application 40 h or more prior to MI induced a steady decline, culminating in a 40% reduction in chromosome pairing at about 80 h from MI. Between 48 and 35 h before MI (late premeiotic interphase to early zygotene) meiocytes underwent a period of active nucleolar fusion. The time, therefore, at which the colchicine sensitive aspects of chromosome pairing were completed coincided with the completion of nucleolar fusion. From comparison with other findings it was concluded that there is a colchicine sensitive bouquet stage which appears in leptotene and early zygotene; this bouquet is responsible for active nucleolar fusion and final close association between homologous chromosomes.

scholarly journals A separation-of-function ZIP4 wheat mutant allows crossover between related chromosomes and is meiotically stable

2021 ◽  
Author(s):  
Azahara C. Martín ◽  
Abdul Kader Alabdullah ◽  
Graham Moore
Keyword(s):  
Wheat Breeding ◽  
Wild Type ◽  
Grain Number ◽  
Homologous Chromosomes ◽  
Chromosome 5B ◽  
Correct Pairing ◽  
New Gene ◽  
Multiple Genomes ◽  
Mutant Lines ◽  
Homoeologous Chromosomes

ABSTRACTMany species, including most flowering plants, are polyploid, possessing multiple genomes. During polyploidisation, fertility is preserved via the evolution of mechanisms to control the behaviour of these multiple genomes during meiosis. On the polyploidisation of wheat, the major meiotic gene ZIP4 duplicated and diverged, with the resulting new gene TaZIP4-B2 being inserted into chromosome 5B. Previous studies showed that this TaZIP4-B2 promotes pairing and synapsis between wheat homologous chromosomes, whilst suppressing crossover between related (homoeologous) chromosomes. Moreover, in wheat, the presence of TaZIP4-B2 preserves up to 50% of grain number. The present study exploits a ‘separation-of-function’ wheat Tazip4-B2 mutant named zip4-ph1d, in which the Tazip4-B2 copy still promotes correct pairing and synapsis between homologues (resulting in the same pollen profile and fertility normally found in wild type wheat), but which also allows crossover between the related chromosomes in wheat haploids of this mutant. This suggests an improved utility for the new zip4-ph1d mutant line during wheat breeding exploitation, compared to the previously described CRISPR Tazip4-B2 and ph1 mutant lines. The results also reveal that loss of suppression of homoeologous crossover between wheat chromosomes does not in itself reduce wheat fertility when promotion of homologous pairing and synapsis by TaZIP4-B2 is preserved.

Live observation of fission yeast meiosis in recombination-deficient mutants

2001 ◽  
Vol 114 (15) ◽  
pp. 2843-2853 ◽  
Author(s):  
Monika Molnar ◽  
Jürg Bähler ◽  
Jürg Kohli ◽  
Yasushi Hiraoka
Keyword(s):  
Fission Yeast ◽  
Chromosome Segregation ◽  
Meiotic Division ◽  
Chiasma Formation ◽  
Homologous Chromosomes ◽  
Yeast Meiosis ◽  
Mutant Cells ◽  
Random Level ◽  
Meiosis I ◽  
Chromosome Disjunction

Regular segregation of homologous chromosomes during meiotic divisions is essential for the generation of viable progeny. In recombination-proficient organisms, chromosome disjunction at meiosis I generally occurs by chiasma formation between the homologs (chiasmate meiosis). We have studied meiotic stages in living rec8 and rec7 mutant cells of fission yeast, with special attention to prophase and the first meiotic division. Both rec8 and rec7 are early recombination mutants, and in rec7 mutants, chromosome segregation at meiosis I occurs without any recombination (achiasmate meiosis). Both mutants showed distinct irregularities in nuclear prophase movements. Additionally, rec7 showed an extended first division of variable length and with single chromosomes changing back and forth between the cell poles. Two other early recombination deficient mutants (rec14 and rec15) showed very similar phenotypes to rec7 during the first meiotic division, and the fidelity of achiasmate chromosome segregation slightly exceeded the expected random level. We discuss possible regulatory mechanisms of fission yeast to deal with achiasmate chromosome segregation.

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