1,721,123 research outputs found
Molecular and chromosomal markers for evolutionary considerations in Torpediniformes (Chondrichthyes, Batoidea)
No full textMarcatori cromosomici e molecolari nello studio dell’evoluzione dei Torpediniformes (Condrichthyes, Batoidea)
No full textSex-related genomic sequences in cartilaginous fish: An overview
No full textSex determination and differentiation are key events in the development of either the testis or ovary in fish. Sex determination mechanisms include environmental and genetic regulation. Research on sex determination systems and their related genes have been implemented in the teleost species, but the amount of information about these genes in cartilaginous fish is very scarce. This paper summarizes the few available data on molecular studies and chromosome localization of specific sequences useful to discriminate between various chromosome pairs in the common torpedo, Torpedo torpedo, and in the scyliorhinid coral catshark, Atelomycterus marmoratus, species that do not have morphologically distinct sex chromosomes. In addition, recent results obtained by sequence analysis of foxl2, a female-specific gene expressed during early phases of gonadal development in interesting key-species, such as the holocephalian Callorhinchus milii, is discussed. Nevertheless, the mechanism of sex determination in cartilaginous fish remains largely unknown. Further research needs to be carried out regarding the importance of basic and applied sex determination studies in fish, including chromosomal distribution of sex-related sequences. © 2013 S. Karger AG, Basel
Engineered Nanomaterials for Environmental and Health Applications
No full textIn recent decades, the rapid advancement of nanotechnology has led to the introduction of engineered nanomaterials (ENMs) into the environment, whether through deliberate actions or accidental releases [...
Comparative genomics in Torpediniformes (Chondricthyes, Batoidea)
No full textDue of their basal position in the vertebrate phylogenetic tree, the study on Elasmobranch genetics and cytogenetics can provide interesting information on the evolution of all vertebrates.
In recent years, different molecular approaches, among them the physical mapping of specific nucleotide sequences on chromosomes and the use of these genomic portions for the construction of phylogenetic trees, were used to study the relationships between the different taxonomic groups of cartilaginous fishes. Particularly in Torpediniformes these are even more controversial. In addition, the species have different karyological parameters, the diploid number varies from 28 to 86 elements, with different morphology of the karyotype. Our aim was to report all the molecular markers that were used to reconstruct the phylogenetic position of Torpediniformes respect to the other Batoidea and to discriminate between the various chromosome pairs in the endemic species in the Mediterranean Sea. The 5S and 18S ribosomal DNA, the HpaI and Alu SINE, the telomeric (TTAGGG)n and the spermatogenesis-related sequences have proved particularly useful. These last genomic segments were also useful to differentiate between the male and the female karyotypes. Moreover the torpedoes showed a particular genomic organization, especially Torpedo torpedo; in this species large quantities of highly repeated DNA and a characteristic distribution of heterochromatin, which is never centromeric, were observed. The pattern of hybridization of these markers confirmed that the genome of Torpediniformes and particularly that of T. torpedo is now more than ever, unique, such as to consider this species as a "model species" to study
CHONDRICHTHYAN CYTOGENETICS - A COMPARISON WITH TELEOSTEANS
No full textCytogenetic studies on cartilaginous fish conducted in recent years have shown that these vertebrates have peculiarities associated both with the karyotypes and the size and composition of their DNAs. Although the data for this group, which includes about 1000 extant species, are still fragmentary, there appear to be more differences than similarities with teleosts; e.g., chromosome sets are characterized by a high diploid number (2n=up to 106) and are often rich in acrocentric elements and in microchromosomes. From the quantitative standpoint, chondrichthyan genomes are relatively large (2C=up to 34 pg DNA/n), exhibiting sometimes wide interspecific variability (Squalidae). The few studies on genome composition for these species have revealed marked difference between chondrichthyans and teleosteans in the ratio of the amount of GC-rich DNA to the total increase in genome. Moreover, thermal denaturation of the genomes of six selachians revealed derived curves that are characteristic of heterogeneity in nucleotide distribution, which has not been evidenced in most of the teleosteans investigated thus far. Finally, for the first time in selachians, an investigation was conducted using restriction enzymes, the results of which showed a pattern of chromosome labeling that was in some cases (Alu I) similar to and in others (Hae III, Hind III) different from that of teleosteans. © 1991 Springer-Verlag New York Inc
Selachian cytogenetics: a review
No full textThe karyotype of Chondrichthyes is still the least investigated among vertebrates. Over the last 40 years, the karyotypes of 63 out of the 1100 known species (5.73%) have been described in literature, namely seven squalomorph, one squatinomorph, 20 galeomorph, 33 batoid and two holocephalian species. Generally, the diploid number ranges from a minimum of 28 to a maximum of 106 elements, with more frequent values observed between 50 and 100 chromosomes. None of the four superorders is characterized by a peculiar chromosome set or morphology; the number of uniarmed and biarmed elements is variable in all the karyotypes, and microchromosomes are often present. The general trend in all groups seems to be a progressive reduction of the telocentric chromosome number in the most specialized species, followed by the loss of the microchromosomes. Polyploidy, followed by diploidization events and Robertsonian rearrangements, might have played a key role in the karyological evolution of elasmobranch fish. Chondrichthyes have the largest genome sizes among vertebrates, with the exception of dipnoans and urodeles. In the whole class, the species examined vary greatly in size, from 3 to 34 pg/N: the lowest values have been observed in holocephalians, while galeoids and batoids have a DNA amount ranging from 5 to 15 pg/N. Squaloids show heterogeneous DNA amounts, ranging from 8 to 34 pg/N. In more recent years, karyological studies have provided new data on the characterization of selachian karyotypes by C-banding, NOR staining, restriction enzymes in situ digestion and FISH with specific DNA probes, such as telomeric and SINE sequences
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