A cytogenetic study was conducted on an Astyanax eigenmanniorum population from the Caetano Stream (18°44' 56" S/ 048°18' 39" W) -in Uberlândia, MG, Brazil -showing a modal diploid number of 48 chromosomes in the standard male and female karyotypes. However, in several specimens it was also possible to observe metaphases with one or two B chromosomes, increasing the diploid number to 49 or 50 chromosomes, respectively. The supernumerary chromosomes were totally heterochromatic and highlighted after C-banding. The silver-stained nucleolus organizing regions (Ag-NORs) were located in at least five chromosomes of the standard karyotype, thus characterizing a multiple NOR system in the species. This is the first occurrence of an A. eigenmanniorum population with 2n = 48 chromosomes, bearing supernumerary chromosomes.

ABSTRACTthe genus Astyanax is one of the most numerous of the family Characidae, comprising a large number of similar-shaped species, but displaying innumerable karyotypic variations in its chromosome number and/or structure. the literature describes A. fasciatus populations with diploid chromosome numbers varying from 2n = 45 to 2n = 48. in this study, A. fasciatus specimens captured in the Araguari river (Alto Paraná basin) were cytogenetically characterized, revealing a diploid chromosome number of 2n = 46. the nucleolar organizing regions (nors), detected with silver nitrate staining, showed a multiple system with two pairs of marked chromosomes. these findings are congruent with those of other studies involving populations of the same species.Keywords: cytogenetics, Astyanax, Astyanax fasciatus. ReSumoAnálise cromossômica em Astyanax fasciatus (Pisces, Characidae) da população do Rio Araguari, uberlândia, mG, Brasil o gênero Astyanax é um dos mais numerosos da família Characidae, englobando um grande número de espécies muito semelhantes na forma, mas que apresentam inúmeras variações cariotípicas no número e/ou estrutura cromossômica. Encontram-se descritas na literatura populações de A. fasciatus com o número diplóide variando de 2n = 45 a 2n = 48 cromossomos. no presente trabalho, espécimes de Astyanax fasciatus da população da calha do rio Araguari (bacia do Alto Paraná), foram caracterizados citogeneticamente. o número diplóide observado foi 2n = 46 cromossomos. As regiões organizadoras de nucléolo (nors), detectadas com nitrato de prata, apresentaram um sistema múltiplo, com dois pares de cromossomos marcados. Esses dados estão de acordo com os descritos para outras populações da mesma espécie.Palavras-chave: citogenética, Astyanax, Astyanax fasciatus.

ABSTRACT. In order to optimize preparations of bee metaphases, we tested cobalt chloride, which has been used as a metaphase inducer in other organisms, such as hamsters and fish. Four microliters of 65 mM cobalt chloride aqueous solution was topically applied to larval and pupal stages of the stingless bee Melipona scutellaris. The cerebral ganglion was removed after treatment and prepared for cytogenetic analysis. Identically manipulated untreated individuals were used as controls. The number of metaphases was increased 3-fold in treated individuals compared to controls. The micronucleus test showed no mutagenic effects of cobalt chloride on M. scutellaris cells. We concluded that cobalt chloride is a metaphase-inducing agent in M. ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 12 (2): 2032-2037 (2013 Cobalt chloride induces metaphase in stingless bees 2033 scutellaris, thus being useful for cytogenetic analyses.