Reducing Breakage of Metaphase Plates in Feulgen-Stained Root Tips of Wheat; Ice-Water Storage Before Squashing

Cytogenetic studies with aneuploid series in wheat usually involve a large number of chromosome counts. The reliability of results and the speed of this work are limited by several factors: (1) method of pretreatment for contraction and spreading of chromosomes, (2) the staining procedure, (3) the method of maceration, and (4) the technique of squashing. These determine the final quality of squash preparations.     

A case of translocation D-, t(lp+)

Summary A severely retarded, dystrophic, hypotonic boy with joint hyperflexibility, jaw anomalies, cerebral hypoplasia and failure to thrive is reported. He died at the age of 8 months. Clinical and biochemical investigation revealed predominantly normal values. An unusual type of palmar crease was found. Chromosomal studies showed a translocation, probably a mosaic with normal cells. The parents are chromosomally normal.     

Trypanosoma cruzi: analysis of the population dynamics of heterogeneous mixtures

Utilizing the previously reported inter-clonal differences in total DNA/organism, flow cytometry was used to analyze the population dynamics of Trypanosoma cruzi clone mixtures growing in liquid medium or vertebrate cells. The growth of clone mixtures in liquid medium can be described by unique parameters reflecting exponential growth rate (r), stationary phase population density (1/k), and the interaction between the clones (h). The relative numbers of each clone in the population change rapidly with time and the results are in quantitative agreement with mathematical models of competitive population growth. The relationship between the parameters for T. cruzi is such that, in general, there is no dynamic equilibrium with coexistence of clones with different growth rates; under all culture protocols, the faster growing clone will prevail. A computer simulation of the vertebrate cell cycle of T. cruzi suggests that clone mixtures grow relatively independently; the basic attributes of the model were substantiated experimentally. Although wide fluctuations in the proportion of each clone released occurred, the faster growing clone again predominated. Finally, these results underline the importance of working with well-defined clones in the laboratory to avoid inconsistencies and paradoxical results and stress the importance of the rapid isolation of single cell clones from clinical specimens when studying the relationship of the parasite to human disease.     

Trypanosoma cruzi: Biological Characterization of Clones Derived from Chronic Chagasic Patients. II. Quantitative Analysis of the Intracellular Cycle1

The complete intracellular cycle of five cloned stocks of Trypanosoma cruzi was quantified. Marked but stable interclonal differences were found in the length of the pre-replicative lag period (18.2-34.2 h), amastigote doubling lime (8.6-21.5 h), and duration of the complete intracellular cycle (96-215 h). Strong correlations were demonstrated between these characteristics as well as to the growth rate of the epimastigote stage of the same clones grown in liquid medium. These data demonstrate that the marked heterogeneity of the natural population of T. cruzi extends to the intracellular cycle of the parasite and has important implications for our understanding of Chagas’ disease.     

Supercoil-induced Z-DNA formation within 5'-end of chicken myb proto-oncogene

We have analyzed the recently sequenced and characterized 2.9 kb fragment derived from the 5'-end of chicken myb proto-oncogene with respect to structural perturbations induced by DNA supercoiling. Within the first intron a 50 bp sequence stretch was localized, starting approximately 450 nucleotides downstream from putative ATG initiation codon, which forms a non-B-DNA structure. Fine mapping with structural probes revealed the three adjacent regions with imperfect purine-pyrimidine alternation creating together relatively long Z-forming tract, parts of which may undergo a B-Z DNA transition at different superhelical densities.