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Key Clinical Message: Primary GBM of the optic nerve and chiasma should be included in the differential diagnosis of progressive lesions despite initial treatment; clinicians should avoid delay in confirming the histology to initiate proper treatment and improve prognosis. Primary GBM of the optic nerve or chiasma is very rare. The characteristics of this condition have not been well‐described, which poses difficulties in establishing the correct diagnosis, affecting the treatment and the prognosis. We present a case of GBM of the optic chiasma diagnosed through an open biopsy at our centre. Following the PRISMA statement, we also conducted a systematic review after protocol registration in PROSPERO (CRD42021285855). We searched Medline and Embase through Ovid from inception until December 31, 2021. Two reviewers independently screened the studies. Studies were eligible for inclusion if they reported cases of primary GBM confined to the optic nerve or chiasma as the initial radiological diagnosis. A 77‐year‐old female was referred for progressive visual loss lasting 8 weeks. MRI revealed a suspected lesion in the left chiasma. The patient's vision deteriorated further despite initially diagnosing an inflammatory process and empirical treatment with corticosteroids. Subsequently, the patient underwent an open biopsy and surgical debulking. Histology, including epigenetic analysis, confirmed GBM grade IV. Radiochemotherapy was administered. The patient died 19 months after surgery. We identified 45 similar cases (22 female) reported in 35 studies between 1949 and 2020. The mean age of the cases was 61 (SD = 14.6). Most cases were misdiagnosed and mistreated accordingly, so there was a median delay of 8 weeks (IQR: 5–14 weeks) in obtaining histological confirmation of the diagnosis, delaying the initiation of appropriate treatment. Five cases became no treatment since the patients died shortly after the delayed histologic diagnosis. The Kaplan–Meier estimate indicated that most patients died within 20 months of presentation, with a 1‐year survival rate of 50%, and untreated cases had very low survival rates compared to treated cases. Primary GBM of the optic nerve and chiasma is a rare condition primarily affecting adults. The rarity of this condition contributes to initial misdiagnosis, mistreatment, and delays in confirming the histology and initiating appropriate treatment. The prognosis remains poor, but treatment, including surgery and radiochemotherapy, improves survival. [ABSTRACT FROM AUTHOR]

Summary: Mutations affecting crossover (CO) frequency and distribution lead to the presence of univalents during meiosis, giving rise to aneuploid gametes and sterility. These mutations may have a different effect after chromosome doubling. The combination of altered ploidy and mutations could be potentially useful to gain new insights into the mechanisms and regulation of meiotic recombination; however, studies using autopolyploid meiotic mutants are scarce.Here, we have analyzed the cytogenetic consequences in colchicine‐induced autotetraploids (colchiploids) from different Arabidopsis mutants with an altered CO frequency.We have found that there are three types of mutants: mutants in which chiasma frequency is doubled after chromosome duplication (zip4, mus81), as in the control; mutants in which polyploidy leads to a higher‐than‐expected increase in chiasma frequency (asy1, mer3, hei10, and mlh3); and mutants in which the rise in chiasma frequency produced by the presence of two extrachromosomal sets is less than doubled (msh5, fancm). In addition, the proportion of class I/class II COs varies after chromosome duplication in the control.The results obtained reveal the potential of colchiploid meiotic mutants for better understanding of the function of key proteins during plant meiosis. This is especially relevant considering that most crops are polyploids. [ABSTRACT FROM AUTHOR]

Copyright of Critical Hermeneutics: Biannual Journal of Philosophy is the property of Universita degli Studi di Cagliari and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

During meiosis, the chromosome axes and synaptonemal complex mediate chromosome pairing and homologous recombination to maintain genomic stability and accurate chromosome segregation. In plants, ASYNAPSIS 1 (ASY1) is a key component of the chromosome axis that promotes inter-homolog recombination, synapsis and crossover formation. Here, the function of ASY1 has been cytologically characterized in a series of hypomorphic wheat mutants. In tetraploid wheat, asy1 hypomorphic mutants experience a reduction in chiasmata (crossovers) in a dosage-specific manner, resulting in failure to maintain crossover (CO) assurance. In mutants with only one functional copy of ASY1, distal chiasmata are maintained at the expense of proximal and interstitial chiasmata, indicating that ASY1 is required to promote chiasma formation away from the chromosome ends. Meiotic prophase I progression is delayed in asy1 hypomorphic mutants and is arrested in asy1 null mutants. In both tetraploid and hexaploid wheat, single asy1 mutants exhibit a high degree of ectopic recombination between multiple chromosomes at metaphase I. To explore the nature of the ectopic recombination, Triticum turgidum asy1b-2 was crossed with wheat-wild relative Aegilops variabilis. Homoeologous chiasmata increased 3.75-fold in Ttasy1b-2/Ae. variabilis compared to wild type/Ae. variabilis, indicating that ASY1 suppresses chiasma formation between divergent, but related chromosomes. These data suggest that ASY1 promotes recombination along the chromosome arms of homologous chromosomes whilst suppressing recombination between non-homologous chromosomes. Therefore, asy1 mutants could be utilized to increase recombination between wheat wild relatives and elite varieties for expediting introgression of important agronomic traits. [ABSTRACT FROM AUTHOR]

During meiosis, the chromosome axes and synaptonemal complex mediate chromosome pairing and homologous recombination to maintain genomic stability and accurate chromosome segregation. In plants, ASYNAPSIS 1 (ASY1) is a key component of the chromosome axis that promotes inter-homolog recombination, synapsis and crossover formation. Here, the function of ASY1 has been cytologically characterized in a series of hypomorphic wheat mutants. In tetraploid wheat, asy1 hypomorphic mutants experience a reduction in chiasmata (crossovers) in a dosage-specific manner, resulting in failure to maintain crossover (CO) assurance. In mutants with only one functional copy of ASY1, distal chiasmata are maintained at the expense of proximal and interstitial chiasmata, indicating that ASY1 is required to promote chiasma formation away from the chromosome ends. Meiotic prophase I progression is delayed in asy1 hypomorphic mutants and is arrested in asy1 null mutants. In both tetraploid and hexaploid wheat, single asy1 mutants exhibit a high degree of ectopic recombination between multiple chromosomes at metaphase I. To explore the nature of the ectopic recombination, Triticum turgidum asy1b-2 was crossed with wheat-wild relative Aegilops variabilis. Homoeologous chiasmata increased 3.75-fold in Ttasy1b-2/Ae. variabilis compared to wild type/Ae. variabilis, indicating that ASY1 suppresses chiasma formation between divergent, but related chromosomes. These data suggest that ASY1 promotes recombination along the chromosome arms of homologous chromosomes whilst suppressing recombination between non-homologous chromosomes. Therefore, asy1 mutants could be utilized to increase recombination between wheat wild relatives and elite varieties for expediting introgression of important agronomic traits.

Simple Summary: Bimodal karyotypes, including both large chromosomes and microchromosomes, are mainly found in reptiles, birds, fish, and insects, but not mammals. Studies of microchromosomes are currently of great interest. The karyotype of the snake Vipera berus is a prime example of a bimodal karyotype. We conducted a comparative cytogenetic study of meiotic (synaptonemal complexes in prophase I) and mitotic chromosomes. A significant asynchrony in the assembly of meiotic bivalents and the dynamics of the appearance of the mismatch repair protein MLH1 were analyzed, and a high level of meiotic recombination was shown. Furthermore, minor species-specific markers of the V. berus meiotic karyotype were identified. Vipera berus is the species with the largest range of snakes on Earth and one of the largest among reptiles in general. It is also the only snake species found in the Arctic Circle. Vipera berus is the most involved species of the genus Vipera in the process of interspecific hybridization in nature. The taxonomy of the genus Vipera is based on molecular markers and morphology and requires clarification using SC-karyotyping. This work is a detailed comparative study of the somatic and meiotic karyotypes of V. berus, with special attention to DNA and protein markers associated with synaptonemal complexes. The karyotype of V. berus is a remarkable example of a bimodal karyotype containing both 16 large macrochromosomes and 20 microchromosomes. We traced the stages of the asynchronous assembly of both types of bivalents. The number of crossing-over sites per pachytene nucleus, the localization of the nucleolar organizer, and the unique heterochromatin block on the autosomal bivalent 6—an important marker—were determined. Our results show that the average number of crossing-over sites per pachytene nucleus is 49.5, and the number of MLH1 sites per bivalent 1 reached 11, which is comparable to several species of agamas. [ABSTRACT FROM AUTHOR]

La ricerca percorre la mia esperienza personale prima di entrare all'università e dopo, da quando ho iniziato a insegnare e a fare ricerca. L'identità del ricercatore si pluralizza dopo aver criticato il metodo della dialettica e della sintesi, per affermare una visione transitiva basata su una costellazione mobile che richiama alcuni concetti mutanti e fondamentali: feticismo, sincretismo, polifonia, eteronomia, diaspora, amicizia, stupore, ubiquità, genere , indisciplina e Marx66. L'etnografia si presenta come un tentativo di attraversare antropologia e filosofia visto trovarsio al crocevia del chiasma.

Copyright of MATRIZes is the property of Universidade de Sao Paulo, Programa de Pos Graduacao em Ciencias da Comunicacao and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Our study aimed to report the normative values for optic nerve diameter in different age groups in MR imaging (MRI) in the pediatric population and to find a cut-off value for diagnosis in different age groups to be used for the diagnosis of optic glioma in patients with Neurofibromatosis 1(NF1). Orbital MRI obtained from 2011 to 2021 for children with and without NF1 were reviewed. Patients were divided into three groups: NF1 with glioma (group 1, n = 38), NF1 without glioma (group 2, n = 57), and healthy controls (group 3, n = 295). Two radiologists assessed diameter and tortuosity using validated criteria. The optic nerve measurements were obtained by two radiologists in two plans (axial and coronal sections) at five locations; retroocular, midsegment, and prechiasmatic segment on axial plane and retroocular segment and chiasmatic on coronal plane. Optic nerves were divided into 4 age groups: 0–2 years, 2–6 years, 6–12 years, and 12–18 years. It was observed that optic nerve diameters increased with age in healthy individuals. In subjects in groups 1 and 2, the mean diameter of the optic nerve was significantly greater at all locations compared with control individuals. Tortuosity scores were significantly associated in NF1 subjects with optic glioma than in NF1 subjects without optic glioma. We present the normative values obtained by measuring optic nerve diameters in pediatric populations (0–18 years) on MRI of our center. A rapid increase in optic nerve diameter was observed in the first 6 years of life, followed by a slower increase. Quantitative reference values for optic nerve diameter will benefit the development of objective diagnostic criteria for optic nerve gliomas (ONGs) secondary to NF1. • Some asymptomatic cases of optic glioma can also be detected while scanning for NF-1. • Risk assessment is difficult in asymptomatic patients with NF-1, due to the lack of valid biomarkers for optic glioma. • Quantitative reference values for optic nerve may contribute to objective diagnostic criteria for optic gliomas. [ABSTRACT FROM AUTHOR]

It is a matter of great serendipity that while studying cytogenetics of Eclipta alba (L.) Hassk. we reported B chromosome. It is the maiden study regarding the reporting of B chromosomes in this plant species as per our knowledge. During the meiotic study of Eclipta alba (L.) Hassk maximum three B chromosomes were reported in Bhringraj. The study deals with the effect of B chromosomes on A chromosome chiasma frequency, chiasma distribution and pollen fertility in Eclipta alba (L.) Hassk. Results suggest that B chromosome enhances the chiasma frequency, and also increases variations in carrier and non- carrier pollen mother cells (PMCs). Moderate reduction in fertility of carrier plants, in contrast to non-carriers could also recorded. With regard to earlier investigations, the possible mechanism of action of B-chromosomes has been discussed. Aside from their intrinsic enigmatic properties B-chromosomes might be useful experiment tool to study the wider issues of genome organization and evolution in plants and make them insightful. [ABSTRACT FROM AUTHOR]

Introduction. Symptoms of lesions of the I, VII and IX pairs of cranial nerves during SARS-CoV-2 infection are observed in about a third of cases. Isolated bitemporal hemianopia as a symptom of optic nerve damage at the chiasmal level in patients with COVID-19 has not been described yet. Case report. A 65-year-old man with a history of arterial hypertension and myocardial infarction and confirmed COVID-19 infection with severe lung damage on computed tomography. Patient developed bitemporal hemianopia, confirmed by the Donders test, on the second day of hospitalization. CT scan revealed no lesions and organic pathology in the parachiasmatic region and in the substance of the brain. Two days later, there was a complete restoration of lateral vision. Discussion. The most likely cause of bitemporal hemianopia was microthrombotic or inflammatory lesion at the chiasmal level. Risk factors for thrombotic complications: male gender, age 65, history of cardiovascular diseases, increased D-dimer levels, and signs of systemic inflammation (increased levels of C-reactive protein, fibrinogen, lactate dehydrogenase, and ferritin). An alternative hypothesis for the development of chiasmal syndrome may be direct viral invasion SARS-CoV-2 of the central nervous system.

This article engages with the notion of an aesthetic “chiasma” developed by the Japanese philosopher Imamichi Tomonobu in the 1960s. According to Imamichi, the nineteenth century saw an inversion of basic ideas associated with the artistic traditions of East and West. While in the East, the earlier dominance of expression was replaced by an emphasis on the importance of representation, for the West, the idea of mimesis-representation was superseded by a focus on expression. Imamichi’s argument remain infuential. Drawing on a series of philologically relevant reflections by several generations of scholars and artists, from Watanabe Kazan to Hashimoto Kansetsu, and situating them in relation to their Western and Chinese counterparts, this article clarifes the developments which occurred and the conficts which emerged over the course of this interaction. In doing so, it demonstrates that Imamichi’s notion of chiasma remains too restricted to capture the degree of exchange between the Eastern and Western aesthetic ideals taking place in modern Japan. The article concludes that Imamichi’s chiasma was made possible by the awkward mapping of a pair of fundamental dualities associated with Eastern and Western thought onto one another, in a manner which reveals more about the geopolitical imperatives of the 1960s than the process of intellectual exchange itself. [ABSTRACT FROM AUTHOR]

Background: Optic pathway gliomas (OPGs) are rare neoplasms where the management strategy is still evolving. The purpose of this study is to present our experience of twenty cases of OPGs with an intent to add to the general fund of knowledge. Materials and Methods: Retrospective chart review of patients with OPGs surgically managed in a single tertiary centre over a period of 5 years. Variables analysed include Age at diagnosis, sex, clinical manifestations, neurofibromatosis (NF1) status, tumour location, treatment modality, symptomatic progression, and complications. Results: Of the 20 patients with OPG in the study with a mean age of 12.8 years, four patients had NF1 and 16 had sporadic OPG. Dimness of vision (80%) and headache (55%) were the most common presenting symptoms. Majority of the tumours were chiasmatic (40%) in location and vision was affected bilaterally. Subtotal resection could be achieved in 12 (60%) partial decompression in 4 (30%) and gross total resection in 2 (10%). Four patients required additional shunt surgery for hydrocephalus. Postoperative radiotherapy was administered to thirteen patients and only one patient received chemotherapy. At the end of a mean follow up period of 44 months tumour recurrence was noticed in 11/20 (55%) patients. Vision improved in none, remained stable in fifteen and deteriorated in five. Three patients (15%) succumbed to tumour regrowth in the follow up period. Conclusions: OPGs are uncommon tumours with unpredictable outcome. Visual deficits are often irreversible and progressive. Curative resection is difficult and adjuvant therapy has variable response. Overall survival rates are good but progression free and survival rates are suboptimal.

Establishment of proper chromosome attachments to the spindle requires elimination of erroneous attachments, but the mechanism of this process is not fully understood. During meiosis I, sister chromatids attach to the same spindle pole (mono-oriented attachment), whereas homologous chromosomes attach to opposite poles (bi-oriented attachment), resulting in homologous chromosome segregation. Here, we show that chiasmata that link homologous chromosomes and kinetochore component Dam1 are crucial for elimination of erroneous attachments and oscillation of centromeres between the spindle poles at meiosis I in fission yeast. In chiasma-forming cells, Mad2 and Aurora B kinase, which provides time for attachment correction and destabilizes erroneous attachments, respectively, caused elimination of bi-oriented attachments of sister chromatids, whereas in chiasma-lacking cells, they caused elimination of mono-oriented attachments. In chiasma-forming cells, in addition, homologous centromere oscillation was coordinated. Furthermore, Dam1 contributed to attachment elimination in both chiasma-forming and chiasma-lacking cells, and drove centromere oscillation. These results demonstrate that chiasmata alter attachment correction patterns by enabling error correction factors to eliminate bi-oriented attachment of sister chromatids, and suggest that Dam1 induces elimination of erroneous attachments. The coincidental contribution of chiasmata and Dam1 to centromere oscillation also suggests a potential link between centromere oscillation and attachment elimination.

This paper traces the genealogy of reversibility, chiasma, and chiasme in Merleau-Ponty's writings and offers a new characterisation of his later ontology in terms of a multi-layered chiasme-focused topology informed by subtle differences and interconnections among these notions. We need to grasp the significance of reversibility not only in terms of constant recoil and impossible overlap but also of its situatedness in the crisscrossing between Dasein and things, and between the inside/invisible and the outside/visible. "Chiasma" was initially introduced as a reference to the intersection of perspectives. Merleau-Ponty deploys it to articulate macroscopic insights concerning the nature of philosophy and the interweaving connections between self, other, and the world. In comparison, "reversibility" is primarily used to describe the microscopic bond between touching-touched and perceiving-perceived. I argue that, as Merleau-Ponty's ultimate choice of wording, "chiasme" incorporated the significance of both "reversibility" and "chiasma." A chiasme-focused topology that retains the significance of all three of the terms would serve to better convey the import of Merleau-Ponty's later ontology, which aims to dissolve and to re-configure our conceptions about being, body, self, and the other from within and from below. [ABSTRACT FROM AUTHOR]

Background: Patients with visual loss from macroadenomas compressing their optic apparatus may also have concomitant age-related visual pathology such as cataracts. How these two pathologies interact with each other is not well documented. Objective: The interaction between these two pathologies in elderly patients is the subject of this study. Methods: We identified a series of non-functioning macroadenoma patients over age 50 years with tumors compressing the chiasm who underwent transsphenoidal surgery at our institution between 2004 and 2018. Pre- and post-operative visual complaints, tumor size and extent of resection were analyzed. Prevalence of the diagnosis of cataract and prevalence of cataract surgery in each decade were compared with national averages. Results: We identified 200 patients who met selection criteria. 18% of these patients had a diagnosis of cataract and 12.5% had cataract surgery. Compared with the Eye Diseases Prevalence Research Group (EDPRG) study, the prevalence of cataract surgery was 2.5 times the national average of 5.1%. 32% of these patients had no improvement in their vision after cataract surgery but 76% improved after transsphenoidal surgery. Conclusions: We reported a high prevalence of cataract surgery in patients over age 50 in patients with pituitary macroadenomas compressing the optic pathway compared with national averages in patients without adenomas. While visual loss from adenoma likely precipitated more cataract surgeries in this group of patients, some who may not have required it, those patients with cataracts who did not have their cataracts extracted were less likely to recover vision after transsphenoidal surgery. Addressing both pathologies is beneficial. [ABSTRACT FROM AUTHOR]

This article presents the results of comparative studies of the frequency and distribution of chiasmata in pollen mother cells (PMCs) in five diploid tomato species, Solanum lycopersicum, S. pimpinellifolium, S. peruvianum, S. habrochaites, and S. neorickii, and one autotetraploid species, S. pimpinellifolium. It was established that under the same growing conditions, the total chiasma frequency in the cell depended on the species. At the same time, the green-fruited species S. peruvianum, S. neorickii, and S. habrochaites differed in distal chiasma frequency, while the red-fruited species S. lycopersicum and S. pimpinellifolium differed in interstitial chiasma frequency. It was shown that the total chiasma frequency in PMCs of plants of one species is a stable index of recombination potential that does not depend on the growing conditions. The redistribution between distal and interstitial chiasmata was found to be more variable, depending on the species, year, geographic growth conditions. In autotetraploid, the chiasma frequency per bivalent was lower than that in diploid S. pimpinellifolium plants, primarily due to interstitial chiasmata, the frequency of which remained at the level characteristic for diploid plants. It was concluded that the recombination plasticity of the tomato genomes was due to the redistribution of chiasmata along bivalents, and not to the change in their number in the cell. [ABSTRACT FROM AUTHOR]

Polyploid organisms provide additional opportunities to study meiosis in a more complex context since more than two potential homologous chromosomes are available. When the chromosome complement of a diploid individual is duplicated, each chromosome is accompanied by one identical and two homologous chromosomes within the same nucleus. In this situation, a competition in pairing/synapsis/chiasma formation between identical and homologous (but not necessarily identical) chromosomes can occur. Several studies have been conducted in different species to address whether there are preferences in crossover formation between identical rather than homologous chromosomes. In this study, multivalent and chiasma frequencies were cytologically analyzed in synthetic autotetraploids of Arabidopsis thaliana including the accessions Col, Ler, and the Col/Ler hybrid. Fluorescence in situ hybridization was conducted to identify each chromosome at metaphase I. The new Col and Ler tetraploids showed high multivalent frequencies, exceeding the theoretical 66.66% expected on a simple random end-pairing model, thus indicating that there are more than two autonomous synaptic sites per chromosome despite their small size. However, a significant excess of bivalent pairs was found in the Col/Ler hybrid, mainly due to the contribution of chromosomes 2 and 3. The mean chiasma frequencies of the three artificial autotetraploids were about twofold the corresponding mean cell chiasma frequencies of their diploid counterparts. The relative contribution of each chromosome to the total chiasma frequency was similar in the three genotypes, with the exception of a lower contribution of chromosome 3 in the hybrid. Preferences for chiasma formation between identical and homologous chromosomes were analyzed in Col/Ler 4x, taking advantage of the cytological differences between the accessions: variations in the size of the 45S rDNA region on the short arm of chromosome 2 and changes in the size and localization of the 5S rDNA region in chromosome 3. We observed a different behavior of chromosomes 2 and 3, i.e., random chiasma formation between identical and homologous chromosomes 2, and preferences for chiasma formation between homologous chromosomes 3. Hence, our results reveal the existence of chromosome-specific mechanisms responsible for these preferences.

The production of gametes (sperm and eggs in mammals) involves two sequential cell divisions, meiosis I and meiosis II. In meiosis I, homologous chromosomes segregate to different daughter cells, and meiosis II resembles mitotic divisions in that sister chromatids separate. While in principle the process is identical in males and females, the time frame and susceptibility to chromosomal defects, including achiasmy and cohesion weakening, and the response to mis-segregating chromosomes are not. In this review, we compare and contrast meiotic spindle assembly checkpoint function and aneuploidy in the two sexes. [ABSTRACT FROM AUTHOR]

Polyploid organisms provide additional opportunities to study meiosis in a more complex context since more than two potential homologous chromosomes are available. When the chromosome complement of a diploid individual is duplicated, each chromosome is accompanied by one identical and two homologous chromosomes within the same nucleus. In this situation, a competition in pairing/synapsis/chiasma formation between identical and homologous (but not necessarily identical) chromosomes can occur. Several studies have been conducted in different species to address whether there are preferences in crossover formation between identical rather than homologous chromosomes. In this study, multivalent and chiasma frequencies were cytologically analyzed in synthetic autotetraploids of Arabidopsis thaliana including the accessions Col, L er , and the Col/L er hybrid. Fluorescence in situ hybridization was conducted to identify each chromosome at metaphase I. The new Col and L er tetraploids showed high multivalent frequencies, exceeding the theoretical 66.66% expected on a simple random end-pairing model, thus indicating that there are more than two autonomous synaptic sites per chromosome despite their small size. However, a significant excess of bivalent pairs was found in the Col/L er hybrid, mainly due to the contribution of chromosomes 2 and 3. The mean chiasma frequencies of the three artificial autotetraploids were about twofold the corresponding mean cell chiasma frequencies of their diploid counterparts. The relative contribution of each chromosome to the total chiasma frequency was similar in the three genotypes, with the exception of a lower contribution of chromosome 3 in the hybrid. Preferences for chiasma formation between identical and homologous chromosomes were analyzed in Col/L er 4x, taking advantage of the cytological differences between the accessions: variations in the size of the 45S rDNA region on the short arm of chromosome 2 and changes in the size and localization of the 5S rDNA region in chromosome 3. We observed a different behavior of chromosomes 2 and 3, i.e., random chiasma formation between identical and homologous chromosomes 2, and preferences for chiasma formation between homologous chromosomes 3. Hence, our results reveal the existence of chromosome-specific mechanisms responsible for these preferences. [ABSTRACT FROM AUTHOR]

Consanguineous marriage was examined as a risk factor for Down syndrome birth. We genotyped Down syndrome family trios using short tandem repeat markers on 21q‐to interpret the parental and meiotic stage of origin of errors as well as to record recombination profile along long arm of chromosome 21. We then compared nonconsanguineous (N = 811) group with‐the consanguineous (N =157) marriages. We report for the first time that consanguineous marriage is associated with an increased risk for nondisjunction of chromosome 21 in oocytes‐during the second meiotic division. We observed the absence of recombination more frequently in younger mothers in nonconsanguineous meiosis I cases. This was in contrast to an equal distribution of nonrecombinant cases across the age categories in the meiosis I consanguineous group. Moreover, the non‐consanguineous group exhibited preferential telomeric recombination in meiosis I error among younger women and centromeric recombination in meiosis II errors in older women. In contrast, the consanguineous group exhibited medially placed recombination events in both meiosis I and meiosis II nondisjunction errors. Additionally, we recorded reduced maternal age at conception in the‐consanguineous group. These findings suggest novel risk factors associated that increase the risk of chromosome 21 nondisjunction in the families with consanguinity. [ABSTRACT FROM AUTHOR]

Supernumerary 'B' chromosomes are non-essential components of the genome present in a range of plant and animal species--including many grasses. Within diploid and polyploid ryegrass and fescue species, including the forage grass perennial ryegrass (Lolium perenne L.), the presence of B chromosomes has been reported as influencing both chromosome pairing and chiasma frequencies. In this study, the effects of the presence/absence of B chromosomes on genetic recombination has been investigated through generating DArT (Diversity Arrays Technology) marker genetic maps for six perennial ryegrass diploid populations, the pollen parents of which contained either two B or zero B chromosomes. Through genetic and cytological analyses of these progeny and their parents, we have identified that, while overall cytological estimates of chiasma frequencies were significantly lower in pollen mother cells with two B chromosomes as compared with zero B chromosomes, the recombination frequencies within some marker intervals were actually increased, particularly for marker intervals in lower recombination regions of chromosomes, namely pericentromeric regions. Thus, in perennial ryegrass, the presence of two B chromosomes redistributed patterns of meiotic recombination in pollen mother cells in ways which could increase the range of allelic variation available to plant breeders. [ABSTRACT FROM AUTHOR]

Synaptic mutants are the subject of a special concern to cytologists and geneticists as they hold the variability in their recombination pattern. Seeds of Trachyspermum ammi (L.) Sprague (ajwain) were treated with Ethyl Methane Sulphonate (EMS) solution at 3 different concentrations viz. 0.1%, 0.3% and 0.5% for 5 h, prepared in potassium phosphate buffer with 7.0 pH. During meiotic observation of 0.3% concentration of EMS treated population of ajwain, the Pollen Mother Cells (PMCs) of the two plants showed a desynaptic behavior with a high frequency of a univalent formation along with a few bivalents at diakinesis/metaphase I. Apparently, EMS might be involved in the formation of substandard synaptic proteins which reduced the chiasma formation, suggesting that EMS has the ability to generate the male sterile lines. Along with the univalent formation, other various chromosomal aberrations were also analyzed in the subsequent stages of meiotic division viz. laggards, bridges, unequal separation, and disturbed polarity with abnormal tetrads. Thus, both the desynaptic plants displayed a high incidence of pollen sterility. The present investigation made an attempt to understand the meiotic behavior of desynapsis and its consequences on the pollen fertility of the ajwain crop. [ABSTRACT FROM AUTHOR]