B chromosomes in two fish species, genus Rhamdia (Siluriformes, Pimelodidae).
Specimens belonging to two fish species genus Rhamdia were cytogenetically analysed from seven localities in Brazil and Argentina. In addition to the 58 chromosomes of the basic karyotype, one to five metacentric B chromosomes were observed carrying conspicuous heterochromatic blocks on the distal regions of both chromosome arms. These B chromosomes are mitotically stable and, in the two best-sampled populations in R. hilarii (Lobo and 29 reservoirs), they showed frequency distributions fitting a binomial distribution, though Bs were more frequent in the latter. The presence of B chromosomes with the same appearance in R. quelen suggests an ancient origin for these B chromosomes, presumably prior to speciation from a common ancestor.
Fenocchio
A S
AS
Universidad Nacional de Misiones, Facultad de Ciencias Exactas, Quimicas y Naturales, Departamento de Genetica, Felix de Azara 1552, 3300 Posadas, Misiones, Argentina. afenocch@fceqyn.unam.edu.ar
Bertolo
L A
LA
Takahashi
C S
CS
Camacho
J P
JP
D000818:Animals; D002875:Chromosomes; D005399:Fishes / Q000235:genetics*; D007621:Karyotyping; D013045:Species Specificity