We found that the sex-ratio of an amphigenic strain of Sciara ocellaris varied widely from progenies with few males to progenies containing a larger proportion of males, with single-sex progenies being rare. The sex-ratio distributions were dependent on the temperature at which the stocks of flies were raised, with the sex-ratio distributions being symmetrical (i.e. about 50% males) at 18°C and 20°C while at the higher temperatures of 24°C and 28°C the distributions were skewed toward a high proportion of females with the mean proportion of males decreasing to about 30-37% per progeny. Temperature-shift experiments showed that high temperatures were effective only during the last stages of female pupal development plus a period after adult emergence, stages corresponding to oocyte maturation. When imagine females were exposed to temperatures as low as 12°C the sex-ratio distributions of their progeny were skewed toward a high proportion of males per progeny. No differential fecundity was involved in these progeny sex-ratio modifications. Egg-to-adult survival was lower at 18°C and 28°C but no correlations with skewing in the sex ratio distributions were observed, indicating that modifications in progeny sex-ratio did not involve the differential survival of a particular sex.

We have determined the deleterious effects of singlet oxygen (1O2), generated by thermal decomposition of the water-soluble endoperoxide 3,3'-(1,4-naphthylidene)dipropionate (NDPO2), on plasmid DNA. By following the electrophoretic mobility of DNA on agarose gels, we detected single and double strand breaks induced by treatment with NDPO2. The vector employed was a mammalian shuttle vector and the mutagenic consequences of these damages were investigated, using as mutation target the supF suppressor tRNA gene. A high increase of the mutation frequency, over the background, was observed in plasmids transfected in bacteria or after passage through mammalian cells. Trapping agents and quencher effects and other controls confirm the involvement of 1O2 in DNA damage and mutagenicity. These findings indicate that 1O2 can induce DNA lesions which are repaired by an error-prone process in prokaryotic and eukaryotic cells.

In order to characterize the molecular nature of singlet oxygen (1O2) induced mutations in mammalian cells, a SV40-based shuttle vector (pi SVPC13) was treated with singlet oxygen arising from the thermal decomposition of the water-soluble endoperoxide of 3,3'-(1,4-naphthylidene) dipropionate (NDPO2). After the passage of damaged plasmid through monkey COS7 cells, the vector was shuffled into E. coli cells, allowing the screening of supF mutants. The mutation spectrum analysis shows that single and multiple base substitutions arose in 82.5% of the mutants, the others being rearrangements. The distribution of mutations within the supF gene is not random and some hotspots are evident. Most of the point mutations (98.4%) involve G:C base pairs and G:C to T:A transversion was the most frequent mutation (50.8%), followed by G:C to C:G transversion (32.8%). These results indicate that mutagenesis in mammalian cells, mediated by 1O2-induced DNA damage, is targeted selectively at guanine residues.

Language is one field of science education research that has received a lot of attention lately. This is revealed by an increase in the number of papers that deal with this subject (Carlsen, 2007). One of the topics related to language in science education that still need to be further explored is reading and writing in science. Here, some questions that can represent border knowledge are: How school science texts can be characterized? Is there any relation between these texts and their reading comprehension? Possible answers to these questions have dealt with the linguistic features of science texts (