Differences in the synaptic pattern in two autotetraploid cultivars of rye with different quadrivalent frequencies at metaphase I

Genome ◽  
1999 ◽  
Vol 42 (4) ◽  
pp. 662-667
Author(s):  
M Martínez ◽  
C Cuadrado ◽  
J Sybenga ◽  
C Romero
Keyword(s):  
Electron Microscopy ◽  
Synaptonemal Complex ◽  
Prophase I ◽  
Quadrivalent Frequency ◽  
Surface Spread ◽  
Metaphase I

Synaptic behaviour of the two tetraploids rye cultivars Gigantón (G) and Tetrapico (T) displaying significant differences in their quadrivalent frequencies at metaphase I was analyzed by electron microscopy in surface-spread prophase I nuclei. A different behaviour was observed between the two cultivars; the synaptonemal complex (SC) quadrivalents frequency being significantly higher in G than in T at prophase I. Moreover, the G SC quadrivalents had more synaptic partner exchanges (SPEs) and their location was more distal than the T SC quadrivalents. However, inverse findings were found at metaphase I, the quadrivalent frequency was higher in T than in G. The role that different factors, mainly the number and location of the SPEs and the frequency and distribution of chiasmata, could play in the evolution from prophase I to metaphase I in both cultivars is discussed.Key words: autotetraploid rye, synaptonemal complex, spreading.

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.

Chromosome pairing and potential for intergeneric recombination in some hypotetraploid somatic hybrids of Lycopersicon esculentum (+) Solanum tuberosum

Genome ◽  
1993 ◽  
Vol 36 (6) ◽  
pp. 1032-1041 ◽  
Author(s):  
J. H. de Jong ◽  
A. M. A. Wolters ◽  
J. M. Kok ◽  
H. Verhaar ◽  
J. van Eden
Keyword(s):  
Solanum Tuberosum ◽  
Lycopersicon Esculentum ◽  
Synaptonemal Complex ◽  
Chromosome Pairing ◽  
Somatic Hybrids ◽  
Cytogenetic Study ◽  
Unreduced Gametes ◽  
Root Tip ◽  
Prophase I ◽  
Metaphase I

Three somatic hybrids resulting from protoplast fusions of a diploid kanamycin-resistant line of tomato (Lycopersicon esculentum) and a dihaploid hygromycin-resistant transformant of a monohaploid potato (Solanum tuberosum) line were used for a cytogenetic study on chromosome pairing and meiotic recombination. Chromosome counts in root-tip meristem cells revealed two hypotetraploids with chromosome complements of 2n = 46 and one with 2n = 47. Electron microscope analyses of synaptonemal complex spreads of hypotonically burst protoplasts at mid prophase I showed abundant exchanges of pairing partners in multivalents involving as many as eight chromosomes. In the cells at late pachytene recombination nodules were found in multivalents on both sides of pairing partner exchanges, indicating recombination at both homologous and homoeologous sites. Light microscope observations of pollen mother cells at late diakinesis and metaphase I also revealed multivalents, though their occurrence in low frequencies betrays the reduction of multivalent number and complexity. Precocious separation of half bivalents at metaphase I and lagging of univalents at anaphase I were observed frequently. Bridges, which may result from an apparent inversion loop found in the synaptonemal complexes of a mid prophase I nucleus, were also quite common at anaphase I, though the expected accompanying fragments could be detected in only a few cells. Most striking were the high frequencies of first division restitution in preparations at metaphase II/anaphase II, giving rise to unreduced gametes. In spite of the expected high numbers of balanced haploid and diploid gametes, male fertility, as revealed by pollen staining, was found to be negligible.Key words: synaptonemal complex, recombination, chromosome pairing, somatic hybrid, Lycopersicon esculentum (+) Solanum tuberosum.

Genetic and cytogenetic analyses of the A genome of Triticum monococcum. IV. Synaptonemal complex formation in autotetraploids

Genome ◽  
1987 ◽  
Vol 29 (2) ◽  
pp. 309-318 ◽  
Author(s):  
C. B. Gillies ◽  
J. Kuspira ◽  
R. N. Bhambhani
Keyword(s):  
Synaptonemal Complex ◽  
Theoretical Models ◽  
Triticum Monococcum ◽  
Pachytene Nucleus ◽  
Lateral Element ◽  
A Genome ◽  
Cytogenetic Analyses ◽  
The Difference ◽  
Quadrivalent Frequency ◽  
Metaphase I

Electron microscopy of synaptonemal complex spreads from autotetraploid Triticum monococcum (2n = 4x = 28) revealed a minimum mean of 3.59 multivalents per zygotene–pachytene nucleus. The range of values was from 1 to 6 multivalents per nucleus. Most of the multivalents were quadrivalents with single, medially located pairing partner switch points. Lateral element pairing switches, particularly the few multiple switches, were often accompanied by extensive asynapsis around the switch point. The synaptonemal complex multivalent frequency is considerably higher than the metaphase I quadrivalent frequency previously reported for the same material. Calculations of expected pachytene quadrivalent frequency from metaphase I data, using several published theoretical models, gave values that did not agree with the results obtained here. The difference between the multivalent frequencies at pachytene and metaphase I does not appear to be the result of a correction process. Instead, it could be caused by a combination of preferential pairing or crossing-over and the effects of the position of partner switches and asynapsis associated with switches. Key words: autotetraploid, multivalents, synaptonemal complex, pairing effects.

Indiscriminate synapsis in achiasmate Allium fistulosum L. (Liliaceae)

1992 ◽  
Vol 103 (2) ◽  
pp. 415-422
Author(s):  
G. Jenkins ◽  
A. Okumus
Keyword(s):  
Synaptonemal Complex ◽  
Allium Fistulosum ◽  
Cell Nuclei ◽  
Male Sterile ◽  
Allium Species ◽  
Lateral Element ◽  
Synaptonemal Complexes ◽  
Independent Process ◽  
Surface Spread ◽  
Metaphase I

Seedlings of Allium fistulosum (2n=2x=16) were treated with aqueous colchicine with the intention of inducing tetraploidy. One treated, but undoubled, diploid mutant is described which consistently fails to form any chiasmata at diakinesis and metaphase I of meiosis. Electron microscopy of whole-mount surface-spread synaptonemal complex complements of pollen mother cell nuclei revealed that the achiasmate condition is probably due not only to the failure to complete synapsis, but also to the indiscriminate way in which the chromosomes form synaptonemal complexes during meiotic prophase. Synapsis begins and progresses with complete disregard to homology, with frequent exchanges of pairing partners resulting in the formation of multiple associations comprising heterologous chromosomes. Intrachromosomal synapsis is also evident as fold-back loops. Up to 78% of lateral element length is incorporated into synaptonemal complex, the morphology of which is not unlike that of normal A. fistulosum and other Allium species described previously. However, all the synaptonemal complexes are ineffective in terms of supporting chiasmata, since 16 univalents enter metaphase I and disjoin irregularly at anaphase I. The mutant is as a consequence completely male sterile. The synaptic behaviour observed confirms that the recognition of homology is an independent process and not a prerequisite for synaptonemal complex formation. It is hoped this mutant will be a valuable tool for probing the molecular basis of homology.

Meiotic chromosome structure: relationship between the synaptonemal complex and the chromatid cores

Genome ◽  
1992 ◽  
Vol 35 (6) ◽  
pp. 1054-1061 ◽  
Author(s):  
J. S. Rufas ◽  
J. L. Santos ◽  
M. Diez ◽  
J. A. Suja
Keyword(s):  
Electron Microscopy ◽  
Light Microscopy ◽  
Synaptonemal Complex ◽  
Chromosome Structure ◽  
Sex Chromosome ◽  
Meiotic Chromosome ◽  
Light And Electron Microscopy ◽  
Structure Relationship ◽  
Surface Spread ◽  
Relationship Of

The development of silver-stained synaptonemal complexes (SCs) and of chromatid cores was analyzed in squashed and surface-spread grasshopper spermatocytes using light and electron microscopy, respectively. This study was conducted to determine the relationship of the two chromosome structures and then obtain more insight into the meiotic chromosome structure. Pachytene cells observed by light microscopy showed thin silver-stained threads, representing SCs, along the centre of the bivalents. However, fully formed SCs, and an axial element corresponding to the univalent sex chromosome, appeared when these cells were observed by electron microscopy. During early diplotene no silver-stained threads were observed by light microscopy. However, fragmentation of the SCs was apparent in cells at the same stage when observed by electron microscopy. Both light and electron microscopy showed that chromosome cores were first detected in homologues of late diplotene – early diakinesis cells. During diakinesis the cores were not continuous but were interrupted where interstitial chiasmata occur. In prometaphase I – metaphase I cells these cores appeared continuous and double, i.e., each chromatid clearly showed its own core. We propose a model whereby the associated cores of sister chromatids act as frameworks for the formation of the SC lateral elements.Key words: meiosis, chromosome structure, synaptonemal complex, chromatid core.

scholarly journals The rad9 Gene of Coprinus cinereus Encodes a Proline-Rich Protein Required for Meiotic Chromosome Condensation and Synapsis

Genetics ◽  
1996 ◽  
Vol 142 (4) ◽  
pp. 1105-1117
Author(s):  
Lisa C Seitz ◽  
Keliang Tang ◽  
W Jason Cummings ◽  
Miriam E Zolan
Keyword(s):  
Synaptonemal Complex ◽  
Meiotic Chromosome ◽  
Chromatin Condensation ◽  
Complex Form ◽  
Coprinus Cinereus ◽  
Wild Type ◽  
Normal Completion ◽  
Type C ◽  
Surface Spread ◽  
Metaphase I

Abstract The rad9 gene of Coprinus cinereus is essential for the normal completion of meiosis. We examined surface-spread preparations of wild-type and rad9-1 nuclei from the meiotic stages of karyogamy through metaphase I, and we determined the primary sequence, structure, and meiotic expression of the rad9 gene. In wild-type C. cinereus, karyogamy is followed by condensation and alignment of homologous chromosomes. Condensation and axial core development largely precede synapsis, which often initiates at telomeres. A diffuse diplotene phase coincides with dissolution of the synaptonemal complex, and subsequently chromosomes further condense as the cells progress into metaphase I. In contrast, although karyogamy and nucleolar fusion are apparently normal in rad91 basidia, only short stretches of synaptonemal complex form. These correlate with stretches of condensed chromatin, mostly at apparent chromosome ends, and regions of presumptive triple synapsis are numerous. rad9-1 basidia enter the diffuse stage of early diplotene, and then 50% of these cells enter metaphase I by the criteria of nucleolar elimination and at least some chromatin condensation. rad9 gene expression is induced after gamma irradiation and during meiosis. The gene has 27 exons and encodes a predicted protein of 2157 amino acids, with a proline-rich amino terminus.

Spreading synaptonemal complexes of B isochromosomes in the grasshopper Omocestus burri

Genome ◽  
1994 ◽  
Vol 37 (6) ◽  
pp. 1035-1040 ◽  
Author(s):  
A. L. del Cerro ◽  
A. Fernández ◽  
J. L. Santos
Keyword(s):  
Electron Microscopy ◽  
Meiotic Pairing ◽  
Synaptonemal Complexes ◽  
Peripheral Location ◽  
Hairpin Loops ◽  
Pairing Model ◽  
Similarities And Differences ◽  
Surface Spread ◽  
Pairing Behaviour ◽  
Metaphase I

Meiotic pairing behaviour of one and two B isochromosomes (iso-Bs) in the grasshopper Omocestus burri was analysed by electron microscopy in surface-spread prophase I nuclei and compared with light microscopic observations of metaphase I. Iso-Bs display a peripheral location in the surface-spread nuclei and early pairing relative to that of the long members of the A set. Single iso-Bs undergo foldback pairing to give symmetrical hairpin loops. Two iso-Bs may show interarm pairing, mterchromosome pairing, or combinations of the two. Pericentromeric interarm pairing can be delayed in one or both Bs and this delay is mostly observed in bivalents with pairing partner switches. The iso-B bivalent frequencies observed in the three males analysed were 64, 44, and 41%, respectively; the two latter values were significantly lower than the 66% predicted by the random-end-pairing model. There is a reduction in the frequencies of iso-ring univalents (in 1B males) and bivalents (in 2B males) from pachytene to metaphase I. Similarities and differences between the pairing behaviour of iso-Bs from different species are also discussed.Key words: B isochromosomes, meiosis, grasshopper, synaptonemal complexes, pairing partner switches.

Synaptic abnormalities in spread nuclei of Secale. II. Secale vavilovii

Genome ◽  
1995 ◽  
Vol 38 (4) ◽  
pp. 772-779 ◽  
Author(s):  
M. Martínez ◽  
C. Romero ◽  
C. Cuadrado
Keyword(s):  
Synaptonemal Complex ◽  
High Frequency ◽  
Diploid Species ◽  
Chromosome Complement ◽  
Nucleolar Organizer ◽  
Prophase I ◽  
Total Length ◽  
Metaphase I

Secale vavilovii PMCs have more univalents and a lower frequency of bound arms at metaphase I than other diploid Secale species. The spreading technique applied at prophase I showed that the nuclei were able to complete synapsis at pachytene. However, 25% of the nuclei analyzed, which had more than 90% of their total length paired, showed two abnormalities: long fold-back loops, which were located mainly on the nucleolar organizer bivalent, and pairing-partner switches, probably involving all the chromosome complement. These synaptic abnormalities are unusual in diploid species and give rise to a high frequency of nonhomologous pairing regions and, therefore, could produce desynapsis, which could explain the data obtained from metaphase I. The possible origin of the unusual synaptic abnormalities of S. vavilovii is discussed.Key words: S. vavilovii, synaptonemal complex, spreading, synaptic abnormalities.

Meiosis in allopolyploid Crepis capillaris. II. Autotetraploids

Genome ◽  
1994 ◽  
Vol 37 (3) ◽  
pp. 497-505 ◽  
Author(s):  
G. H. Jones ◽  
J. E. Vincent
Keyword(s):  
Meiotic Chromosome ◽  
Positional Distribution ◽  
Chromosome Size ◽  
High Frequencies ◽  
Crepis Capillaris ◽  
Prophase I ◽  
Direct Observations ◽  
Surface Spread ◽  
Pairing Initiation ◽  
Metaphase I

Meiotic chromosome pairing of autotetraploid Crepis capillaris was analysed by electron microscopy of surface-spread prophase I nuclei and compared with light microscopic observations of metaphase I chromosome configurations. Prophase I quadrivalent frequencies are high in all three tetrasomes. (A, D, and C) and partially dependent on chromosome size. At metaphase I quadrivalent frequencies are much lower and strongly dependent on chromosome size. There is no evidence for multivalent elimination during prophase I in this system, and the reduction in multivalent frequency at metaphase I can be explained by an insufficiency of appropriately placed chiasmata. The high frequencies of prophase I quadrivalents far exceed the two-thirds expected on a simple model with two terminal independent pairing initiation sites per tetrasome, suggesting that multiple pairing initiation occurs. Direct observations reveal relatively high frequencies of pairing partner switches (PPSs) at prophase I, which confirms this suggestion. The numbers of PPSs per tetrasome show a good fit to the Poisson distribution, and their positional distribution along chromosomes is random and nonlocalized. These observations favour a model of pairing initiation based on a large number of evenly distributed autonomous pairing sites each with a uniform and low probability of generating a PPS.Key words: autotetraploid, meiosis, Crepis capillaris, multivalent, pairing partner switch.

Normal Synaptonemal Complex and Abnormal Recombination Nodules in Two Alleles of the Drosophila Meiotic Mutant mei-W68

Genetics ◽  
2003 ◽  
Vol 163 (4) ◽  
pp. 1337-1356 ◽  
Author(s):  
Adelaide T C Carpenter
Keyword(s):  
Electron Microscopy ◽  
Synaptonemal Complex ◽  
High Frequency ◽  
Serial Section ◽  
The Other ◽  
Wild Type ◽  
Recombination Nodules ◽  
Section Electron ◽  
Serial Section Electron Microscopy ◽  
Section Electron Microscopy

Abstract The meiotic phenotypes of two mutant alleles of the mei-W68 gene, 1 and L1, were studied by genetics and by serial-section electron microscopy. Despite no or reduced exchange, both mutant alleles have normal synaptonemal complex. However, neither has any early recombination nodules; instead, both exhibit high numbers of very long (up to 2 μm) structures here named “noodles.” These are hypothesized to be formed by the unchecked extension of identical but much shorter structures ephemerally seen in wild type, which may be precursors of early recombination nodules. Although the mei-W68L1 allele is identical to the mei-W681 allele in both the absence of early recombination nodules and a high frequency of noodles (i.e., it is amorphic for the noodle phene), it is hypomorphic in its effects on exchange and late recombination nodules. The differential effects of this allele on early and late recombination nodules are consistent with the hypothesis that Drosophila females have two separate recombination pathways—one for simple gene conversion, the other for exchange.

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