1,721,169 research outputs found
Studio del cariotipo di Gymnothorax tile (Osteichthyes, Anguilliformes).
No full textSTUDIO DEL CARIOTIPO DI GYMNOTHORAX TILE (OSTEICHTHYES, ANGUILLIFORMES).
SALVADORI S., COLUCCIA E., CANNAS R., MILIA A., DEIANA A.M.
Dipartimento di Biologia Animale ed Ecologia, Università di Cagliari, Viale Poetto 1, 09126 Cagliari. [email protected]
In questo lavoro presentiamo lo studio del cariotipo di Gymnothorax tile (Hamilton, 1822), un’anguilliforme appartenente alla famiglia Muraenidae che vive in acque salmastre del Pacifico occidentale e dell’Oceano Indiano; è possibile reperirla nei negozi di pesci per acquario. Questo è il primo studio sul complemento cromosomico di questa specie, in bibliografia sono presenti solo scarse informazioni sulla sua biologia. Sono stati studiati sei esemplari, tutti di sesso femminile da cui sono stati ottenuti i preparati cromosomici mediante colture di sangue.
E’ stato determinato il numero diploide 2n = 42 e per la costruzione del cariotipo è stato misurato l’indice centromerico di ogni coppia cromosomica, utilizzando il software Cromowin System (Amplimedical). I cromosomi sono stati classificati secondo Levan et al., (1964) e ordinati nel cariotipo in due gruppi: uno costituito da 17 coppie di cromosomi meta-, submeta- e subtelocentrici; l’altro da 4 coppie di cromosomi acrocentrici. All’interno dei due gruppi i cromosomi sono stati disposti in ordine di lunghezza decrescente.
L’applicazione del bandeggio C, che evidenzia la localizzazione dell’eterocromatina costitutiva, ha permesso l’identificazione di molte coppie di cromosomi omologhi, caratterizzate da evidenti e peculiari bande eterocromatiche. Tutti i cromosomi del complemento presentano bande eterocromatiche centromeriche, in alcune coppie sono inoltre presenti bande telomeriche e bande intercalari anche molto ampie.
Dal confronto con le altre specie studiate della famiglia Muraenidae si nota che il numero cromosomico riscontrato in G. tile, 2n = 42, è quello modale della famiglia, infatti è presente in 5 delle 7 specie studiate. Per quanto riguarda la struttura del cariotipo, G. tile e G. reevesii presentano un numero di bracci (NF = 76) notevolmente più alto rispetto alle altre specie. In base a studi morfologici e molecolari, la famiglia Muraenidae è ritenuta la più primitiva dell’ordine degli Anguilliformi e da un punto di vista citogenetico, presenta tra i più alti numeri cromosomici e contenuti di DNA/nucleo
Supernumerary chromosomes in different families of Decapod Crustaceans
No full textSUPERNUMERARY CHROMOSOMES IN DIFFERENT FAMILIES OF DECAPOD CRUSTACEANS.
Salvadori S.*, Deiana A.M.*, Coluccia E.*, Milia A.**, Cannas R.* & Cau A*.
Dipartimento di Biologia Animale ed Ecologia*; Dipartimento di Biologia Sperimentale**-
Universita’ di Cagliari, Viale Poetto 1, 09126 Cagliari, Italy.
Supernumerary (B) chromosomes are additional chromosomes, highly polymorphic in number and morphology within populations and species. They show non-Mendelian heredity, can be monosomic or disomic and often asynaptic. B chromosomes are widespread in both animals and plants, and “have been found in all groups of organisms citologically well studied” (Jones and Rees, 1982). The biological role of these chromosomes has been discussed for a long time; several experimental data show that they could affect the fitness of the carrier. Their presence has been also hypotesized in some species of Decapoda because of the remarkable numerical variability in both mitotic and meiotic chromosome counting, but without a cytological demonstration (Roberts, 1969; Hughes, 1982; Corni, 1989). In the present study we provide evidence of the presence of chromosomes with some of the features and characteristic behaviour of B chromosomes (Jones & Rees, 1982; Jones, 1985) in two Decapod species, Palinurus elephas and Nephrops norvegicus, belonging to the Palinuridae and Nephropidae families respectively. Chromosome preparations were obtained from testicular tissue using a modification of the air-drying technique. C- and fluorochrome- banding and restriction enzyme-induced banding (RE) allowed a sharp differentiation and a clear identification of chromosomes with features typical of B chromosomes in terms of heterochromatin content, asynapsis and distorted segregation. The presence of these chromosomes can, at least partially, account for the numerical variability already observed in the karyotype of these species.
In Nephrops norvegicus C-banding as well as Dde I-induced banding identified three groups of B chromosomes with different features. Some of them were the largest chromosomes of the complement. C- and DdeI- banding showed that one/two of these chromosomes are only partially heterochromatic, while all the others are completely heterochromatic. Q-banding was useful to show intercalary and subtelomeric bands in the large B chromosomes as well as entirely Q-positive short arms in some small submetacentric chromosomes. In meiotic division I, B chromosomes appeared tightly condensed and asynaptic. Distorted segregation was indicated in metaphases II from the same meiocyte by their random distribution. (Deiana et al., 1996).
In Palinurus elephas, C-banding and HaeIII-induced banding revealed the presence of small B chromosomes, completely heterochromatic and variable in number. In meiosis I, they have been observed forming bivalents, univalents and multivalents.
In Decapoda, B chromosome polymorphism could be a useful marker in investigating the variability among allopatric populations.
CORNI M.G., TRENTINI M. & FROGLIA C., 1989. Karyological study on Nephrops norvegicus (L., 1758)(Astacidea, Nephropidae) in the Central Adriatic sea. Nova Thalas¬sia, 10, 127-131.
DEIANA A.M., COLUCCIA E., MILIA A., SALVADORI S., 1996. Supernumerary chromosomes in Nephrops norvegicus L. (Crustacea, Decapoda). Heredity, 76, 92-99.
HUGHES J.B., 1982. Variability of chromosome number in the lobsters, Homarus americanus and Homarus gammarus. Caryologia, 35(2), 279-289.
JONES R.N. & REES H., 1982. In: B chromosomes, 19-68 (Acade¬mic Press, New York).
JONES R.N., 1985. Are B-chromosomes selfish?. In: Cavalier¬Smith T. (ed.), The evolution of genome size, John Wiley & Sons, 397-425.
ROBERTS F.L., 1969. Possible supernumerary chromosomes in the Lobster, Homarus americanus. Crustaceana, 16, 194-196
Mitotic and meiotic chromosomes of the american lobster Homarus americanus (Nephropidae, Decapoda).
No full textMitotic and meiotic chromosomes of the American lobster Homarus americanus (Nephropidae, Decapoda)
Coluccia E., Cau A., Cannas R., Milia A., Salvadori S., Deiana A.M.
Dipartimento di Biologia Animale ed Ecologia, Università di Cagliari, Viale Poetto 1, 09126 Cagliari, Italy.
Homarus americanus H. Milne Edwards is an important target of North American commercial fishery. The very few karyological studies on this species have documented a remarkable intraspecific numerical variability of the chromosome complement; in order to explain this, the presence of supernumerary chromosomes has been hypothesised though not cytologically demonstrated (Roberts, 1969; Hughes, 1982). Supernumerary (B) chromosomes are additional chromosomes, highly polymorphic in number and morphology within populations and species, and their presence has already been shown in a species of the family Nephropidae (Deiana et al., 1996). In this study we characterise the mitotic and meiotic chromosomes of H. americanus by different banding techniques, and provide evidence of the presence of chromosomes, in this species, with some of the features of the B chromosomes. Chromosome preparations have been obtained from testicular tissue using an air-drying technique. C-banding, fluorochrome-banding and restriction enzyme-induced banding (RE) have allowed a clear identification of meiotic figures and the study of the distribution and structure of heterochromatic regions. These regions are localised on most centromeres and react specifically to the digestion with different REs and to the GC – and AT- specific fluorochrome stainings. Our results point out the GC richness of H. americanus heterochromatin, as shown by the bright fluorescence of most of heterochromatic regions after staining with the GC- specific fluorochrome, chromomycin A3. On the other hand, only few centromeric regions are fluorescent after staining with the AT-specific fluorochromes, DAPI, and Quinacrine. Furthermore the adopted techniques have revealed presence of small B chromosomes, completely heterochromatic, variable in number, and often asynaptic in first meiotic metaphase. The presence of these chromosomes can, at least partially, account for the numerical variability already observed in the karyotype of this species
Biofacies di acritarchi e conodonti come indicatori delle fluttuazioni del livello marino nell’Arenigiano della Cina Meridionale
No full text
From stretching to mantle exhumation in a triangular backarc basin (Vavilov basin, Tyrrhenian Sea, Western Mediterranean)
Full text linkIn this study, we describe the mode of extension of the Vavilov, a fossil backarc basin, triangle-shaped (approximately 240. km-wide and 200. km-long), located between Sardinia margin to the west and Campania margin to the east. We combine the analysis of recent geophysical and geological data, in order to investigate the relationship between the crustal/sedimentary structure and the tectonic evolution of both apex and bathyal parts of the basin. With this aim, we interpret a large data set of multichannel seismic reflection profiles and several well logs. We observe that the apex basin corresponds to a sediment-balanced basin, with a sedimentary infill recording the episodes of basin evolution. In contrast, the distal basin corresponds to an underfilled basin, characterized by localized volcanic activity and a thin sedimentary succession that covers the exhumed mantle. The basin architecture reveals the occurrence of rift and supradetachment basins in the Vavilov rift zone. We find that the rifting of the Vavilov triangular basin was synchronous from the apex to distal regions around a single Euler pole located in Latium, between 5.1 and 1.8. Ma. The kinematic evolution of the Vavilov basin occurred in two stages: initial pure shear mode (5.1-4.0. Ma) that produced high-angle normal faults and syn-sedimentary wedges, followed by simple shear mode (4.0-1.8. Ma) that caused supradetachment basins filled by a Transgressive-Regressive succession that documents high subsidence rates (1.22. mm/y) in the apex region. The final stage of extension in the distal region led to: (i) complete embrittlement of the crust; (ii) direct continuation of crustal faults to upper mantle depth; (iii) serpentinization and mantle exhumation. Based on constraints on the present-day crustal structure of the Vavilov basin, we obtain a stretching value (β. =3.5) and extension rates (3. cm/y) in the bathyal zone analogous to those reported for magma-poor rifted margins
- …
