B chromosomes or supernumerary are genomic structures extra to karyotype pattern A and are present in several groups of eukaryotic organisms such as plants, fungi and animals. These chromosomes may have different origins, including derivation of the autosomes or from sex chromosomes and even being caused by interspecific crosses, which characterizes them as an interesting model for genetic and evolutionary studies. The advent of microdissection technique, which enables the direct isolation of DNA from any chromosomal region, has been providing advances in knowledge and new information about the structure and composition of these genomic elements in a significant number of organisms carrying B chromosomes. In this sense, it is intended to perform the cytogenetic analysis in molecular level of four species of genus Characidium, C. gomesi, C. oiticicai, C. pterostictum and C. alipioi which have B chromosomes in significant stages of differentiation, using the techniques of microdissection, amplification and comparison of the sequences allocated on the genome and the supernumerary chromosomes. The activities, which comprise the isolation of these elements by microdissection (DNAb), as well as genomic DNA extraction (DNAg) from individuals without chromosome B will be followed by mapping and PCR amplification of several repetitive DNA sequences in both types of DNA extracted (DNAg and DNAb), and certainly will result information to better understand the molecular structure of this DNA segment in the genome of these species, as well as clarify aspects of their origin.
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