Citogenética molecular e evolutiva na família Characidae

Abstract

Some species of the genus Moenkhausia have already been studied cytogenetically, and the presence of B chromosomes is considered an interesting feature of these fish. These dispensable supernumerary elements that do not recombine with the standard chromosomes and follow their own evolutionary mechanism vary in number, morphology and distribution, as observed in this study. Karyotypic data are presented here of two populations of M. oligolepis both with 2n = 50 chromosomes and same karyotype formula, distributed at 5m, 16sm and 4st. Besides the modal diploid number, all the individuals presented supernumerary microchromosomes ranging from 0 to 10 in both sexes. The C-banding pattern evidenced heterochromatic blocks located mainly in the pericentromeric region and partly on microchromosomes. Silver impregnation used to evidence the nucleolar organizer regions (Ag-NORs) was variable, with a multiple pattern, and some sites were positive when stained with GC-specific fluorochrome chromomycin A3. The location of the 18S and 5S ribosomal sites were shown to be syntenic in both populations, and the population Taboquinha different chromosomes were labeled, showing intraindividual variations due to translocation or transposition events. The karyotype of M. oligolepis accessed here in detail reinforces the conserved and basal diploid number for the genus, as well as the evolutionary tendency of these fish to present supernumerary chromosomes, probably originated by the formation of isochromosomes and diversified by the accumulation of repetitive DNA and / or elements transposable.