B chromosomes are extra genomic elements to the A complement and may be found in many organisms. In general, these elements might originate intraspecifically from sex or autosomal chromosomes, or even from interespecific hybridizations. The evolution of B chromosomes is quite similar to those of heteromorphic sex chromosomes and includes gene silencing, heterochromatinization processes and repetitive DNA accumulation. New technologies, such as microdissection, method that enables the isolation of single chromosomes, or chromosomal regions, associated with fluorescence in situ hybridization allowed a better knowledge about the composition and molecular structure of B chromosomes. The present study will be developed in the Laboratório de Biologia e Genética de Peixes (IBB/UNESP/BOTUCATU) and its main purpose is to develop molecular cytogenetic analyses in the characid species Astyanax fasciatus. This project includes microdissection of B chromosomes (µB-DNA) and the PCR amplification of several repetitive DNA sequences from this library. After that, comparisons between sequences obtained from the µB-DNA and gDNA will be carried out. This study should present a general pattern of relation between sequences from the A and B chromosomes. The main objective of this study will contribute to the knowledge about molecular content of B chromosomes e generate subsides to uncover the origin of B chromosomes in this species.
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