Biomedical subjects
Publications and source records attributed to W Beçak.
When compared with non-exposed controls, a group of pesticide plant workers chronically exposed to methyl-parathion did not show an increased frequency of chromosome aberrations in lymphocyte cultures. Although methyl-parathion increased chromosome aberrations in cases of intoxication, a chronic exposure to small doses in the work place did not seem to produce the same effect.
A karyological study of some populations of the Odontophrynus occidentalis group (2n = 22) from Argentina is reported. Ammoniacal silver (Ag-AS) and alkaline Giemsa (CBG) staining have been performed on specimens from La Rioja, Mendoza, Malargue, Tamelen, Tapiluque, Valcheta, and Meseta de Somuncura. All populations showed active ribosomal cistrons (NORs) on chromosome 11. Some metaphases of three specimens from Mendoza and five from La Rioja also showed bands on 9. Centromeric and telomeric C-bands were common to all populations, and a block of heterochromatin on both sides of the centromere of 2 was remarkable in all but the La Rioja populations. The specimens from La Rioja showed a similar block of heterochromatin on the short arm of 1. Taxonomic studies of several specimens from these localities revealed differences in larval development, glandular pattern, the size of specimens, etc. As a whole, biological as well as karyological features suggest that the isolated population at La Rioja is a separate entity, at the species level, as described elsewhere.
We analyzed the sexual habits of 80 mothers of normal children and of 33 mothers of children with the Down syndrome (DS). The data were obtained through the psychological interview technique. Unusually long intervals between intercourse at the time of conception were reported more frequently by mothers of DS children. Independent of the mother's age there was an association between the incidence of DS and long intervals between intercourse.
The behavior of the ZW sex bivalent was investigated in female meiosis of the poisonous snake Bothrops jararaca. The Z is euchromatic and synapses end to end with the W. The W chromosome shows a heterochromatic segment distally in the short arm. Pairing occurs between the long arm of the W and the slightly longer arm of the mediocentric Z. A sex vesicle, similar to the one found in the XY placental mammals, does not occur in snakes. The Z and W chromosomes segregate reductionally in the first meiotic division and equationally in the second.
The escape efficiency of two closely related species of frogs, Odontophrynus cultripes (2n = 22) and the tetraploid O. americanus (4n = 44), were compared in a shuttle box and under simulated naturalistic conditions. O. americanus was generally superior to O. cultripes, and females tended to outperform males within both species. The relative inefficiency of O. Cultripes escape behavior was examined in light of the animals' having an elaborate, passive defense mechanism in the form of well marked venom glands. Escape efficiency was highly variable in both species. Possessing twice the amount of DNA, the tetraploid behavioral variation was paradoxically less than that of the diploid, but compatible with what has been found for morphological characters in other organisms.
Chromosome banding patterns obtained by ammoniacal silver staining (Ag-AS) and alkaline Giemsa (CBG) have been analysed in several amphibian species of the genus Odontophrynus from South America. Ag-AS bands were found at secondary constrictions, mainly of chromosomes 4 and 11. The CBG technique revealed centromeric and telomeric constitutive heterochromatin on almost all chromosomes of these species. Moreover, intercalary bands were found at particular sites of several chromosomes. Some inter- and intra-population polymorphisms were found for the Ag-AS and C-banding patterns. The species variability in the number and position of the Ag-AS bands, known to be regions of active ribosomal cistrons, as well as the specific sites of intercalary heterochromatin, are used to discuss the possible evolutionary relationships among these species.
To assess the functional significance of nuclear pore complexes, we have investigated whether the number of pores per nucleus is determined by such factors as the nuclear volume, nuclear surface area, DNA content, or aspects of nuclear activity. Comparisons were made between cell types chosen to permit observation of differences in nuclear pore number as a function of differences in the other qualities measured. The number of nuclear pores was determined by freeze-etching and measurements of nuclear surface and nuclear volume by electron and light microscopy. Pairs of cell strains in culture that contained different numbers of chromosome sets were investigated to examine the relation of pore number to total DNA content. Tetraploid cells of the rat kangaroo (Potorous tridactylus) have almost exactly twice the number of pores found in the parental diploid strain. However, the pore number in diploid grassfrog (Rana pipiens) cells was only 65% greater than in the parental haploid cells. In addition, a polyploid series of nucleated RBC had a 62% pore number increase with each successive increase in ploidy. Diploid cell strains from the canyon mouse (Peromyscus crinitus) and from the cactus mouse (P. eremicus) were compared to test whether a difference reflecting the 36% additional DNA in cells of the latter, associated with extra heterochromatin, existed. Although both were found to have the same number of pores and nuclear surface area, the cells differed in nuclear volume. These observations suggest that the number of nuclear pores is independent of the total amount of nuclear DNA, the nuclear surface area (and, thus, presumably the fraction of DNA that is bound to the nuclear membrane), the nuclear volume, and the size of the genome. Rather, the number of nuclear pores appears to be associated with some aspect of nuclear metabolic activity, e.g., transcriptional capacity or release of products to the cytoplasm. Further evidence for such a view comes from studies of chick embryo erythroblasts. In these, nuclear pore number was found to be lower in associated with the decreasing nuclear transcriptional activity and longer generation times that characterize the successive cell divisions leading to the fully differentiated state. The number of pore complexes reconstructed in the last cell cycles declined in a manner consistent with reutilization of previously formed pores in the absence of new pore synthesis. Challenging this interpretation is the increase in pore number at lower metabolic activity when Xenopus laevis cells are grown at different temperatures. The speculation that pore complexes have a longer half-life in cooler grown Xenopus cells could resolve the discrepancy.
C banded mouse pachytene chromsomes were studied with the light and electron microscopes by the whole mount technique. The X and Y chromosomes show pairing by the long, by the short or by both long and short arms. Assuming Lyon's hypothesis, the latter suggests that the Y segment transferred to the X is intercalar. With the light microscope, a negative image of the synaptonemal complex is evidenced.
C-band patterns of some Odontophrynus species from Brazil are described. O. americanus 2n and 4n are cryptic species similar to O. cultripes 2n, but their C-banding patterns are different. In O. americanus 2n the C-band appears at the secondary constriction of chromosomes 4. In O. americanus 4n and O. cultripes the C-band appears at the secondary constriction of chromosomes 11. O. cultripes chromosomes 2,3 and 6, have also an intercalary band. Furthermore, fine centromeric bands in several weeks old preparations of these species were observed. The possibility of a structural or chemical heterogeneity of those heterochromatic regions is discussed.
The cytogenetic effect of DDT on human blood cultures, in vitro, was investigated. Two types of experiment were carried out: one, in which the DDT concentrations found in the culture media were similar to those found in the plasma of individuals of the Brazilian population (0.06--0.20 mug/ml); in the second experiments, doses ranging from 1 to 15 mug/ml were used. No correlation was found between DDT doses and cells with chromosomal aberrations. The Poisson test of comparison between means showed that at certain DDT concentrations (0.20, 4.05 and 8.72 mug/ml) the proportion of cells with structural aberrations was significantly greater than in the controls.
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Workers from three insecticide plants in direct contact with 2,2-bis (beta-chlorophenyl)-I,I,I,-trichloroethane (DDT) did not differ significantly in the frequencies of cells with chromosomal aberrations when compared with controls from the same plants but not in direct contact with the drug. The same was true when a group of workers from one plant was compared with a control group from the Instituto Butantan, with no history of occupational exposure to DDT. Yet, when the control group from one of the three plants, which showed high DDT plasmic levels, was added to the group in direct contact with the insecticide, the frequency of cells with chromatid aberrations was significantly higher, suggesting that DDT causes chromatid lesions. A positive correlation was found between DDT levels and times of exposure, but being in direct or indirect contact with DDT was not always correlated with the degree of contamination.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.