Ribosomal RNAs (28 + 18S and 5S) and 4S RNA extracted from the chironomid Glyptotendipes barbipes were iodinated in vitro with (125)I and hybridized to the salivary gland chromosomes of G. barbipes and Drosophila melanogaster. Iodinated 18 + 28 S RNA labeled three puffed sites with associated nucleoli on chromosomes IR, IIL, and IIIL of G. barbipes and the nucleolar organizer of Drosophila. Lab...

Age-related morphological and functional changes were studied in the medial mamillary nuclei of the hypothalamus (MMN). The number of nerve cells and the volume of MMN were estimated in both groups of Wistar rats, adult and old (3 and 22 months, respectively) using stereologic methods such as the optical fractionator and Cavalieri's method respectively. The number of neurons and glial cells rem...

The interphase nucleolus in Allhim porrum meristematic cells is characterized by the presence of 1-4 dense fibrillar zones of rather complex organization. Each such zone appears to consist essentially of a convoluted, evacuolated, filamentous structure approximately 1-5 /*m in diameter. At the ultrastructural level, these structures exhibit an intricate array of lacunar spaces each of which is ...

We examined chromosomes of three species of the genus Hypostomus, in order to contribute to the understanding of the karyotype evolution of this group. Specimens of H. ancistroides and H. nigromaculatus displayed differences in karyotype formulas, distribution and location of heterochromatin and nucleolus organizer regions when compared to other populations of the same species. We made the...

Nucleolar organizer regions (NORs) are loops of DNA that transcribe to ribosomal RNA. They are associated with nonhistone nucleoproteins which can be stained with silver (AgNORs). The present retrospective study was done to study the efficacy of AgNOR technique in differentiating between non neoplastic and neoplastic lesions of endometrium and to assess the relationship between AgNOR counts and...

The current taxonomy of most Atelopus species is based on morphological and color data only. Recent studies suggest that A. spumarius may represent a species complex assigned under the same name. Karyotypic data and description of sperm ultrastructure for 13 specimens of A. spumarius are presented here for the first time. A chromosomal analysis revealed 2n = 22 chromosomes, with centromeric het...

It is known that chromosomes occupy non-random positions in the cell nucleus. However, it is not clear to what extent their nuclear positions, together with their neighborhood, are conserved in daughter cells. To address specific aspects of this problem, we used the model of the chromosomes carrying ribosomal genes that are organized in clusters termed Nucleolus Organizer Regions (NORs). We com...

Crossing two parental plants carrying two types of extra chromosomes, 2n+2(5L*7S) by 2n+3(2S*2S) permitted effective selection for individuals with up to eight 2S*2S chromosomes in later generations. The crossing of 2n + 3(2S*2S) by 2n+1( 8S*8L) and by the wild tomato relative, diploid L. pimpinellifolium , produced plants with up to four extra chromosomes. The tolerance of 2S*2S chromosomes th...

The organization of chromosomes is important for various biological processes and is involved in the formation of rearrangements often observed in cancer. In mammals, chromosomes are organized in territories that are radially positioned in the nucleus. However, it remains unclear whether chromosomes are organized relative to each other. Here, we examine the nuclear arrangement of 10 chromosomes...