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For commercial oyster aquaculture, triploidy has significant advantages. To produce triploids, the principal technology uses diploid × tetraploid crosses. The development of tetraploid brood stock for this purpose has been successful, but as more is understood about tetraploids, it seems clear that chromosome instability is a principal feature in oysters. This paper is a continuation of work to investigate chromosome instability in polyploid Crassostrea virginica. We established families between tetraploids-apparently stable (non-mosaic) and unstable (mosaic)-and normal reference diploids, creating triploid groups, as well as tetraploids between mosaic and non-mosaic tetraploids. Chromosome loss was about the same for triploid juveniles produced from either mosaic or non-mosaic tetraploids or from either male or female tetraploids. However, there was a statistically significant difference in chromosome loss in tetraploid juveniles produced from mosaic versus non-mosaic parents, with mosaics producing more unstable progeny. These results confirm that chromosome instability, as manifested in mosaic tetraploids, is of little concern for producing triploids, but it is clearly problematic for tetraploid breeding. Concordance between the results from cytogenetics and flow cytometry was also tested for the first time in oysters, by assessing the ploidy of individuals using both techniques. Results between the two were non-concordant. [ABSTRACT FROM AUTHOR]

Phyllomys (Echimyidae, Rodentia) is a genus of Neotropical rodents with available cytogenetic data restricted to six out of 13 species, mainly based on simple staining methods, without detailed analyses. In this work, we present new karyotypes for Phyllomys lamarum (diploid number 2 n = 56, fundamental number or number of autosomal arms FN = 102) and Phyllomys sp. (2 n = 74, FN = 140) from the state of Minas Gerais, southeastern Brazil. We provide the first GTG- and CBG-banding patterns, silver-staining of the nucleolar organizer regions (Ag-NORs), and fluorescence in situ hybridization (FISH) with telomeric and 45S rDNA probes of Phyllomys. In addition to examining their chromosomes and phenotypic characters, we sequenced mitochondrial DNA from the specimens analyzed to confirm their taxonomic identification. The comparison of the distinctive chromosome complements of our specimens with those of other species of Phyllomys already published allowed us to conclude that chromosome data may be very useful for the taxonomy of the genus, as no two species analyzed presented the same diploid and fundamental numbers (2 n and FN). [ABSTRACT FROM AUTHOR]

The cytogenetic characteristics of 17 species of bushcricket belonging to eight genera of the tribe Barbitistini were examined by fluorescence in situ hybridization with 18S rDNA and (TTAGG n) telomeric as probes and by C-banding, silver, and fluorochrome staining. These markers were used to understand chromosomal organization and evolutionary relationships between genera or species within the same genus. The number of 18S rDNA clusters per haploid genome that co-localized with active nucleolus organizer regions (NORs) ranged from one to five, with the most common pattern being the presence of one NOR-bearing chromosome. This ribosomal cistron was preferentially located in the paracentromeric region of autosomes and very rarely in the sex chromosome. The results demonstrated coincidence between the localization of major ribosomal genes and active NORs and the position of C-band and GC-rich regions. The rDNA/NOR distribution and the composition of chromosome heterochromatin proved to be good cytogenetic markers for distinguishing species and phylogenetic lines and for understanding the genomic differentiation and evolution of Barbitistini. A comparison of cytogenetic and morphological or behavioral traits suggests that morphological and behavioral specialization in this group was not followed by major karyotype modification (except for Leptophyes). However, the occurrence and distribution of different repetitive DNA sites tends to vary among the taxa. [ABSTRACT FROM AUTHOR]

An integrated approach based on cytogenetics, molecular genetics, and ecology was used to examine diversity in the black fly Simulium angulistylum Takaoka & Davies in Thailand. Cytological analysis revealed three cytoforms (A, B, and C) of S. angulistylum differentiated by fixed chromosome inversions. Distributions of these cytoforms were associated with ecology. Cytoforms A and B were found in low-altitude habitats (<600 m above sea level), whereas cytoform C occurred at high altitudes (>1000 m above sea level). Mitochondrial DNA sequences of the cytochrome oxidase subunit I barcoding region revealed significant genetic differentiation among the cytoforms. The mitochondrial DNA haplotype network revealed divergent lineages within cytoforms, indicating additional hidden diversity. Therefore, integrated approaches are necessary for fully understanding black fly biodiversity. Population genetic analysis revealed high genetic structuring that could be due to the habitat preferences of S. angulistylum. Phylogeographic analyses indicated population demographic expansion at the mid-Pleistocene (900 000 years ago), which is older than for other black flies and insects in the Southeast Asian mainland. The high level of genetic structure and diversity, therefore, could also be due to the long demographic history of S. angulistylum. [ABSTRACT FROM AUTHOR]

Interspecific hybridization in Tecoma Juss. was conducted to develop novel forms for the nursery industry. We report fertile hybrids from the cross T. garrocha Hieron. (pistillate parent) × T. stans (L.) Juss. ex Kunth. Leaf morphology of the F1 hybrids of T. garrocha × T. stans was intermediate between the parents. GISH also confirmed hybridity. The F1 hybrids were successfully backcrossed to both parents and self-pollinated to produce BC and F2 progeny. Tecoma garrocha, T. stans, and T. guarume A. DC. 'Tangelo' were self-fertile. The F1 hybrids also were crossed with T. capensis (Thunb.) Lindl. and T. guarume 'Tangelo', resulting in three-species hybrids. FISH conducted on F1 hybrids identified four copies of the 18S internal transcribed spacer region. Further analysis using FISH has the potential to provide information on the evolution of Bignoniaceae and the potential role of polyploidy. [ABSTRACT FROM AUTHOR]

The Brassica B-genome species possess many valuable agronomic and disease resistance traits. To transfer traits from the B genome of B. carinata into B. napus, an interspecific cross between B. napus and B. carinata was performed and a doubled haploid (DH) population was generated from the BC2S3 generation. Successful production of interspecific DH lines as identified using B-genome microsatellite markers is reported. Five percent of DH lines carry either intact B-genome chromosomes or chromosomes that have deletions. All of the DH lines have linkage group J13/B7 in common. This was further confirmed using B. nigra genomic DNA in a fluorescent in situ hybridization assay where the B-genome chromosomes were visualized and distinguished from the A- and C-genome chromosomes. The 60 DH lines were also evaluated for morphological traits in the field for two seasons and were tested for resistance to blackleg, caused by Leptosphaeria maculans, under greenhouse conditions. Variation in the DH population followed a normal distribution for several agronomic traits and response to blackleg. The lines with B-genome chromosomes were significantly different (p < 0.01) from the lines without B-genome chromosomes for both morphological and seed quality traits such as days to flowering, days to maturity, and erucic acid content. [ABSTRACT FROM AUTHOR]

The SalI satellite repeat previously identified in Haliotis L. (abalone) was thought to be present in H. rufescens and absent in H. fulgens. However, we show here that SalI is also found in H. fulgens and is not useful for screening hybrid individuals bred in aquaculture or occurring naturally in the wild. SalI is a family of predominantly subtelomeric tandemly repeated sequences, and sequenced clones revealed clustering to species and little intraspecific variation. Analysis of SalI sequence divergence between Haliotis species of the Northeast Pacific revealed that evolutionary distances correlate well with bathymetric and latitudinal species distributions. Analysis of the structure of the tandem repeats revealed two regions of high sequence conservation that may contain conserved transcription factor binding sites, a surprise for an apparently “non-coding” tandem repeat. We speculate that these regions might be involved in heterochromatin silencing, perhaps mediated via transcriptional activity and RNA interference. The repeats show substantial differences in their chromosomal distributions, even between individuals of the same species, indicating a dynamic organization of repeats, perhaps mediated via sequence homogenization. L’ADN satellite SalI identifié antérieurement chez le Haliotis L. (ormeau nordique) était présumé présent chez le H. rufescens et absent chez le H. fulgens. Les auteurs montrent ici que le satellite SalI est également présent chez le H. fulgens et n’est donc pas utile pour identifier des hybrides produits en aquaculture ou survenant naturellement. Le satellite SalI est une séquence répétée principalement subtélomérique et les clones séquencés suggèrent un groupement sur la base des espèces et peu de variation intraspécifique. L’analyse de la divergence nucléotidique entre les espèces de l’Haliotis du nord-est du Pacifique a révélé que les distances évolutives sont bien corrélées avec la répartition latitudinale et bathymétrique des espèces. L’analyse de la structure des répétitions en tandem révèle deux régions de forte conservation des séquences qui pourraient contenir des sites conservés de liaison de facteurs de transcription, une observation surprenante au sein d’une région apparemment « non-codante ». Les auteurs spéculent que ces régions sont peut-être impliquées dans l’inactivation de l’hétérochromatine obtenue via l’activité transcriptionnelle et l’interférence à l’ARN. Les répétitions affichent des différences substantielles dans leur distribution chromosomique, même entre individus de la même espèce ce qui indique une organisation dynamique des répétitions, peut-être via l’homogénéisation des séquences. [ABSTRACT FROM AUTHOR]

In an earlier study, the progenies of intergeneric hybrids Brassica napus (2n = 38) × Orychophragmus violaceus (2n = 24) were investigated in successive generations (F1–F4) for the cytological phenomenon of parental genome separation during mitotic and meiotic division. In the present study, inbred lines (F5–F8) derived from 1 such hybrid were characterized for morphology, chromosome pairing behaviour, and genome composition. One F5 plant (2n = 31) with slightly yellow petals and 12:19 and 15:16 segregation ratios in its pollen mother cells (PMCs) produced F6 plants with distinct morphological characteristics and wide variations in fertility and chromosome numbers (2n = 25–38). F7 and F8 lines with distinctive morphology and wide ranges in chromsome numbers were established. In PMCs of F7 plants from 4 F6 plants, 0–12 labelled chromosomes from O. violaceus, which predominantly appeared as bivalents, were identified by genomic in situ hybridization. They behaved synchronously with B. napus chromosomes during meiotic division. The results provide molecular cytogenetic evidence of the inclusion of O. violaceus chromosomes in the original hybrids and the cytology in the hybrids documented earlier. They also show that chromosome behaviour was altered and the parental chromosomes became synchronized after successive generations. [ABSTRACT FROM AUTHOR]

The B chromosome of maize undergoes frequent non-disjunction at the second pollen mitosis. In B–A translocations, the B–A chromosome retains the capacity for non-disjunction. We have collected deletion-derivative TB-9Sb stocks. One derivative, the "type 1 telocentric", has a B–9 chromosome that lacks centric heterochromatin. It produces few recessive (non-disjunctional) phenotypes in pollen parent testcrosses of the translocation heterozygote, 9 9–B telo B–9. The finding helped demonstrate the role of centric heterochromatin in non-disjunction. An isochromo some derivative of the type 1 telocentric was also recovered. It was tested in the 9–B 9–B iso B–9 constitution. This is equivalent to 9 9–B telo B–9 in terms of chromosome 9 dosage. Surprisingly, crosses with the isochromosome gave significant levels of recessive phenotypes. In addition, high levels of variegated phenotypes were found. Recently, a circumstance was found that makes inheritance of the type 1 telocentric chromosome somewhat similar to that of the isochromosome. Crosses with hypoploid 9–B 9–B telo B–9 plants showed significant levels of recessive and variegated phenotypes. These crosses were investigated to help explain the source(s) of the phenotypes. Cytological and genetic studies were performed. Centric misdivision was found to account for the variegated phenotypes. A mixture of conventional B non-disjunction and centric misdivision produced the recessive phenotypes. The significance of conventional non-disjunction in the absence of centric heterochromatin is discussed. [ABSTRACT FROM AUTHOR]

In this review, we combine the results of our published and unpublished work with the published results of other laboratories to provide an updated map of the centromeric heterochromatin of chromosome 3 in Drosophila melanogaster. To date, we can identify more than 20 genes (defined DNA sequences with well-characterized functions and (or) defined genetic complementation groups), including at least 16 essential loci. With the ongoing emergence of data from genetic, cytological, and genome sequencing studies, we anticipate continued, substantial progress towards understanding the function, structure, and evolution of centric heterochromatin. [ABSTRACT FROM AUTHOR]

Most fish species show little morphological differentiation in the sex chromosomes. We have coupled molecular and cytogenetic analyses to characterize the male-determining region of the rainbow trout (Oncorhynchus mykiss) Y chromosome. Four genetically diverse male clonal lines of this species were used for genetic and physical mapping of regions in the vicinity of the sex locus. Five markers were genetically mapped to the Y chromosome in these male lines, indicating that the sex locus was located on the same linkage group in each of the lines. We also confirmed the presence of a Y chromosome morphological polymorphism among these lines, with the Y chromosomes from two of the lines having the more common heteromorphic Y chromosome and two of the lines having Y chromosomes morphologically similar to the X chromosome. The fluorescence in situ hybridization (FISH) pattern of two probes linked to sex suggested that the sex locus is physically located on the long arm of the Y chromosome. Fishes appear to be an excellent group of organisms for studying sex chromosome evolution and differentiation in vertebrates because they show considerable variability in the mechanisms and (or) patterns involved in sex determination. [ABSTRACT FROM AUTHOR]

Sexual progenies of asymmetric somatic hybrids between Brassica napus and Crambe abyssinica were analyzed with respect to chromosomal behavior, fae1 gene introgression, fertility, and fatty-acid composition of the seed. Among 24 progeny plants investigated, 11 plants had 38 chromosomes and were characterized by the occurrence of normal meiosis with 19 bivalents. The other 13 plants had more than 38 chromosomes, constituting a complete chromosomal set from B. napus plus different numbers of additional chromosomes from C. abyssinica. The chromosomes of B. napus and C. abyssinica origin could be clearly discriminated by genomic in situ hybridization (GISH) in mitotic and meiotic cells. Furthermore, meiotic GISH enabled identification of intergenomic chromatin bridges and of asynchrony between the B. napus and C. abyssinca meiotic cycles. Lagging, bridging and late disjunction of univalents derived from C. abyssinica were observed. Analysis of cleaved amplified polymorphic sequence (CAPS) markers derived from the fae1 gene showed novel patterns different from the B. napus recipient in some hybrid offspring. Most of the progeny plants had a high pollen fertility and seed set, and some contained significantly greater amounts of seed erucic acid than the B. napus parent. This study demonstrates that a part of the C. abyssinica genome can be transferred into B. napus via asymmetric hybridization and maintained in sexual progenies of the hybrids. Furthermore, it confirms that UV irradiation improves the fertility of the hybrid and of its sexual progeny via chromosomal elimination and facilitates the introgression of exotic genetic material into crop species. [ABSTRACT FROM AUTHOR]

The low glucosinolate Brassica juncea breeding line 1058 was derived from a BC[sub 1] F[sub 3] plant of an interspecific cross between high glucosinolate Indian B. juncea (genome AABB, 2n = 36) line 60143 and B. rapa (genome AA, 2n = 20) canola strain CZY. Line 60143 had 2n = 36 chromosomes (18 bivalents at metaphase I) and strain CZY had 2n = 20 chromosomes (10 bivalents). Line 1058 was nullisomic, with 2n - 2 = 34 chromosomes, with 17 bivalents formed at metaphase I and an even chromosomal segregation of 17:17 at anaphase I. In F[sub 1] hybrid plants of the cross 1058 × CZY, 98.3% of the pollen mother cells had 10 bivalents and seven univalents. This is evidence that plants of line 1058 are nullisomic, missing one pair of B-genome chromosomes.Key words: low glucosinolate mustard, meiotic behaviour, cytogenetics.La lignée 1058 de Brassica juncea à faible teneur en glucosinolates est issue d'un croisement interspécifique entre la lignée 60143 de B. juncea (génome AABB, 2n = 36) à forte teneur en glucosinolates et la lignée double zéro CZY de B. rapa (génome AA, 2n = 20). Les plantes de la lignée 60143 possédaient 36 chromosomes (18 bivalents au stade métaphase I) et les plantes de la lignée CZY possédaient 20 chromosomes (10 bivalents au stade métaphase I). La lignée 1058 était nullisomique (2n - 2 = 34) avec 17 bivalents au stade métaphase I et une ségrégation normale des chromosomes au stade anaphase I. L'analyse du comportement méiotique d'hybrides F[sub 1] issus d'un croisement entre 1058 et CZY a révélé une configuration de 10 bivalents et sept univalents chez 98.3% des cellules mères du pollen, démontrant que les plantes de la lignée 1058 sont nullisomiques pour une paire de chromosomes appartenant au génome B.Mots clés : moutarde à faible teneur en glucosinolates, comportement méiotique, cytogénétique. [ABSTRACT FROM AUTHOR]

The ability to identify individual chromosomes in cytological preparations is an essential component of many investigations. While several computer software applications have been used to facilitate such quantitative karyotype analysis, most of these programs are limited by design for specific types of analyses, or can be used only with specific hardware configurations. MicroMeasure is a new image analysis application that may be used to collect data for a wide variety of chromosomal parameters from electronically captured or scanned images. Unlike similar applications, MicroMeasure may be individually configured by the end user to suit a wide variety of research needs. This program can be used with most common personal computers, and requires no unusual or specific hardware. MicroMeasure is made available to the research community without cost by the Department of Biology at Colorado State University via the World Wide Web at http://www.biology.colostate.edu/MicroMeasure.Key words: MicroMeasure, computer program, chromosome measurement, cytogenetics.La capacité d'identifier des chromosomes individuels au sein de préparations cytologiques constitue une composante importante de plusieurs projets de recherche. Bien que plusieurs logiciels aient été employés pour faciliter les analyses de caryotype quantitatives, la plupart de ces logiciels sont limités, de par leur conception, à des types spécifiques d'analyses ou ne peuvent être employés qu'avec des configurations spécifiques du matériel informatique. MicroMeasure est un nouveau logiciel d'analyse d'images qui peut être employé pour saisir des données en relation avec un grand nombre de paramètres chromosomiques à partir d'images sauvegardées sur support informatique ou encore d'images numérisées. Contrairement aux logiciels semblables, la configuration de MicroMeasure peut être personnalisée afin de rencontrer une vaste gamme de besoins. Ce logiciel peut être utilisé avec la plupart des ordinateurs personnels et ne requiert aucun accessoire inhabituel ou spécifique. MicroMeasure est offert sans frais à la communauté scientifique par le département de Biologie de l'Université Colorado State par le biais du site http://www.biology.colostate.edu/MicroMeasure.Mots clés : MicroMeasure, logiciel, mesures chromosomiques, cytogénétique.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]