The chromosome complement of Chiropodomys gliroides from Peninsular Malaysia consists of two pairs of nucleolar organizer regions (NORs) – the longest acrocentric pair and the small metacentric. The NORs in both pairs are located at the terminal end; in the long acrocentric at the end of the long arm. In the metaphases, at least one element in both pairs exhibited the presence of Ag-NOR activit...

Loricariidae is one of the largest fish families of the world, with about 650 species separated into six subfamilies. To date, cytogenetic data on only 56 species of this family are available. In the present study, the karyotypes of three Ancistrinae species and five Loricariinae species were studied. The lowest diploid number, 2n=38, was observed in Ancistrus n.sp. 1 (Ancistrinae) and the high...

Cytogenetic studies were performed on two sympatric species of Characidium, C. gomesi and C. cf. zebra, from the Grande River basin, Minas Gerais State, Brazil. Although both species had a chromosome number of 50 with a karyotype exclusively consisting of metaand submetacentric chromosomes, interspecific diversity was detected concerning the size of the two first chromosome pairs of the karyoty...

SANDLER (1970) suggested that mutation, abnormal oocyte (abo:2-38), may influence the function of the ribosomal RNA cistrons. We have examined the abo mutation and its interaction with the ribosomal D N A of Drosophila melanogaster. We observed that the expression of the abo phenotype is unstable under the appropriate conditions, a behavior which paralleled changes in the phenotypic expression ...

In dividing eukaryotic cells, nucleoli disperse before mitosis and reform in daughter cells at sites of ribosomal RNA (rRNA) gene clusters that are at the secondary constrictions of chromosomes, called nucleolus organizer regions (NORs). In this study, cDNA clones for a NOR autoantigen (NOR-90) were selected using a specific human autoantibody probe and were subsequently identified to encode an...

By the time ofMontgomery's classic paper on the nucleolus in 1898 (1), there were already 700 or so articles with observations on this nuclear organelle, beginning with a study by Fontana in 1781 entitled "Venom of Vipers." The early cytological emphasis on the nucleolus undoubtedly was due to the high visibility of the organelle in interphase nuclei ofmost cell types ; however, the fact that n...

Chromosome numbers, morphology, and nucleolus organizer region (NOR) locations are useful cytological characters for taxonomic and evolutionary studies. In this study, we provide the first cytogenetic analysis of Phyllomedusa bahiana and Phasmahyla spectabilis, and report new cytogenetic data on variation in NOR numbers and positions in Phyllomedusa rohdei and Phyllomedusa nordestina using conv...