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| Author(s): |
Felippe Lourenço Claro
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB) |
| Defense date: | 2008-12-16 |
| Examining board members: |
Lurdes Foresti de Almeida Toledo;
Claudio de Oliveira;
Yatiyo Yassuda
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| Advisor: | Lurdes Foresti de Almeida Toledo |
| Abstract | |
Fishes present a great diversity in relation to their morphology, habitat and biology. They are found in lakes, rivers, estuaries and oceans, comprising more than 50% of the total number of known vertebrates. Cytogenetic and molecular aspects of the fish fauna have been extensively studied, providing information about their chromosomal relationships and also about the systematic status of several groups. These researches have focused on the description of both chromosomal number and formula as well as the presence of differentiated sex chromosomes, occurrence of B-chromosomes, patterns of heterochromatin distribution, localization of nucleolar organizer regions, restriction or replication banding profiles allowing to locate distinct classes of repetitive DNAs and to identify chromosomal homeologies in order to understand the karyotypic evolution in distinct groups. On the other hand, molecular studies have become of utmost importance in this group, providing essential data about phylogeny of many groups and about repetitive DNA regions and their role in the genome. The union between this approach and cytogenetics has favored a better comprehension about the evolutionary processes associated with visible alterations in specific sequences within the genome at both chromosomal and molecular levels. The genus Gymnotus is composed of representatives with peculiar biological features, which turn them suitable for studies in a variety of biology approaches. Genetic studies in this genus comprise karyotype characterization, analysis of polymorphic NORs, besides studies of molecular markers that, coupled with cytogenetics, have fostered molecular phylogenetic analyzes with inferences on their chromosomal evolution, which have led to a better understanding about the interrelationships in the group. In the present work, we carried out studies about the heterochromatic regions and the repetitive DNAs in this group for a better comprehension about the organization and localization of these sequences in the genome and identification of potential molecular markers. Furthermore, studies related to the karyotype evolution in the species G. carapo and G. sylvius, location of ribosomal genes and molecular analysis of both 5S ribosomal gene and its non-transcribed spacer were performed to provide a better comprehension about the evolution of this gene family in Gymnotus. (AU) | |