Federal University of São Carlos

About: Federal University of São Carlos is a education organization based out in São Carlos, Brazil. It is known for research contribution in the topics: Population & Microstructure. The organization has 16471 authors who have published 34057 publications receiving 456654 citations. The organization is also known as: UFSCar & Federal University of São Carlos.

An overview of marine fish cytogenetics

Abstract: The number of cytogenetic studies of marine fish has increased in recent years. Fish groups, such as Perciformes, which comprises many of the extant marine teleosts of economic importance, show little divergence in chromosome number and most species display a diploid number of 48 acrocentric chromosomes. In the Serranidae, Sparidae, Sciaenidae (Perciformes) and Mugilidae (Mugiliformes) small chromosome variations are restricted to subtle heterochromatin or nucleolar organizer region (NOR) modifications. There appears to exist a strict relationship between both absence of geographic barriers throughout the marine environment and high mobility of these animals (eggs, larvae, or adults), with a rarity of chromosome rearrangement at the macrostructural level. Moreover, a cellular homeostasis might also be important to karyotype maintenance among these fishes, limiting changes in the chromosome complement to cryptic chromosome rearrangements. Other groups, such as Blenniidae, Gobiidae and Scorpaenidae, for instance, show more extensive chromosome diversity, which is probably related to limited mobility. Numerical and structural chromosome polymorphisms and several sexual chromosome systems are recurrent among these fishes. A wide karyotypic diversification also characterizes the Tetraodontiformes, an interesting fish group with peculiar morphological, physiological and ecological characteristics.

A tandemly repetitive centromeric DNA sequence of the fish Hoplias malabaricus (Characiformes: Erythrinidae) is derived from 5S rDNA.

Abstract: A substantial fraction of the eukaryotic genome consists of repetitive DNA sequences that include satellites, minisatellites, microsatellites, and transposable elements. Although extensively studied for the past three decades, the molecular forces that generate, propagate and maintain repetitive DNAs in the genomes are still discussed. To further understand the dynamics and the mechanisms of evolution of repetitive DNAs in vertebrate genome, we searched for repetitive sequences in the genome of the fish species Hoplias malabaricus. A satellite sequence, named 5SHindIII-DNA, which has a conspicuous similarity with 5S rRNA genes and spacers was identified. FISH experiments showed that the 5S rRNA bona fide gene repeats were clustered in the interstitial position of two chromosome pairs of H. malabaricus, while the satellite 5SHindIII-DNA sequences were clustered in the centromeric position in nine chromosome pairs of the species. The presence of the 5SHindIII-DNA sequences in the centromeres of several chromosomes indicates that this satellite family probably escaped from the selective pressure that maintains the structure and organization of the 5S rDNA repeats and become disperse into the genome. Although it is not feasible to explain how this sequence has been maintained in the centromeric regions, it is possible to hypothesize that it may be involved in some structural or functional role of the centromere organization.

Role of Maleated Coupling Agents on the Interface Adhesion of Polypropylene—Wood Composites

Abstract: The main accomplishment of compounding wood-flour with thermo- plastics is an increase in rigidity and specific strength. Filler-matrix interactions play a key role in the composite performance and the strength of the interface is determined by the nature of the coupling agents employed. The coupling efficiency of maleated polypropylene (PP-MAH) with varying MAH content and melt flow index in polypropylene-wood composites has been investigated. A method based on a simplified single rule of mixtures aiming to compare differences in interface adhesion in the presence of PP-MAH is proposed in terms of relaxation spectra of polypropylene-wood composites obtained by dynamic-mechanical thermal analysis (DMTA). The criterion is an attempt to determine an adhesion factor as derived from the relative mechanical damping (tan � ) of the composite as a function of the filler content and temperature. Experimental results deviate from model predictions possibly owing to assumptions of wood-flour as a rigid filler as well as neglect of an interphase volume fraction and its damping characteristics. However, good correlations of coupling efficiency and yield properties have been found for wood composites with homopolymer and copolymer matrices within a range of varying wood-flour content and type of coupling agent. Further evidences of improved matrix-filler interactions, wettability, and filler dispersion in the presence of the PP-MAH are observed by scanning electron microscopy.