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PubMed1983

Evidence for chromosome number reduction and chromosomal homosequentiality in the 24-chromosome Korean frog Rana dybowskii and related species.

The karyotype of the Korean frog Rana dybowskii with its pattern of C-band heterochromatin distribution was numerically analyzed. There are 2n = 24 chromosomes in the karyotype representing a reduction in number from the typical 2n = 26 chromosome karyotype of Rana. The karyotype shows other evidence of reorganization relative to 26-chromosome species. The chromosomes grade smoothly in size from largest to smallest without the two size classes that are characteristic for 26-chromosome species. In contrast to many 26-chromosome species, there are few centromeric C-bands but many interstitial ones. C-bands for each homologous chromosome pair are distinctive. A prominent secondary constriction is located on one of the smallest chromosomes, chromosome 11, in a position similar to that seen in most 26-chromosome species. The karyotype of R. dybowskii is compared to those of other species of Rana known to have 2n = 24 chromosomes; it is most similar to that of R. chensinensis, less so that of R. ornativentris and less still to that of R. arvalis in terms of the positions of centromeres and secondary constrictions. C-bands as well as secondary constrictions in the karyotypes of these frogs show evidence of chromosomal homosequentiality. The process and possible consequences of chromosome number reduction from an ancestral 26-chromosome karyotype is also evident in the karyotypes of these closely allied palearctic frogs. Pericentric inversions followed by fusion of two small elements apparently produced a new chromosome, chromosome 6, occurring originally among northeast Asian populations.

Animals↗
PubMed1983

Quantitative histological study on the thalamic ventro-basal complex of the cat. Numerical aspects of the transfer from medial lemniscal fibers to cortical relay.

A quantitative analysis was carried out on the thalamic ventrobasal (VB) complex of the cat. The following numerical and metrical parameters of the neuronal elements (cells and fibers) were determined: 1. Volume of nucleus: 27.38 mm3 2. Total number of neurons: 243,000 3. Total number of fibers of medial lemniscus: 26,000 4. Volume of arborization space of one lemniscal fiber: 2.26 X 10(6) micrometers 3. Numerical data of relay neurons and lemniscal fibers and their relations as basic factors in the estimation of the degree of divergence and convergence of lemniscal input were calculated and compared. It was found that the probable degree of convergence is four-fold (1-4) and of divergence 27-fold (1-27) with regard to the relationship of fibers and cells in the VB. The quantitative data obtained in the VB and our considerations on convergence and divergence were compared with analogous values obtained for the lateral geniculate body LGB. The differences between the two sensory relay nuclei reflect differences in their modes of impulse transmission.

Animals↗
PubMed1976

Semiautomatic morphometric analysis of the nucleolar development in the nucl. n. oculomotorii of Tupaia belangeri during ontogenesis.

The development during ontogenesis of the nuclear and nucleolar diameters and of the numbers of nucleoli per nucleus in the nucl. n. oculomotorii of 32 male Tupaia belangeri are described. The measurements of the nucleolar diameters were done automatically using the Micro-Videomat (Zeiss, Oberkochen). Increase of the nuclear and nucleolar diameters yielded a nearly sigmoid-shaped curve, which was fitted using the logistic growth function. The "ideal" value of the nucleolar diameter is 3.7 mum with a half value time of 22 days of ontogenesis and an enlargement factor of 1.53. The respective parameters for the nucleus are 12.2 mum, 28 days and 1.27. The ratio of the nuclear to nucleolar diameters decreases exponentially during ontogenesis to a value of 3.3. The validity of these easily determinable morphologic parameters for the RNA-synthesis is discussed. The number of nuclei with 2 or 3 nucleoli decreases during ontogenesis. The relevance of this fact for cell counting is also discussed.

Animals↗