Method to obtain homozygous introgressing segments in Drosophila to identify the presence of hybrid sterility genes of the reproductive isolation

Here, we present for the first time, a method to generate homozygous segmental introgressions, by means of crosses between a pair of synmorphic species. The introgressions were monitored by the cytogenetic method of polygenic chromosome asynapses. Later the introgressions were evaluated in their capacity to produce sterility in segmental males. Also, the smallest segment with the capacity to produce sterility in segmental males was mapped by in situ hybridization of polythene chromosomes, using 8 sequences of BACs clones as probes. Finally, a bioinformatic analysis was carried out to identify the presence of particular genes. From 2 parental strains, D. buzzatii and D. koepferae, 6 simple segmental hybrid lines were generated, whose introgressing segments are distributed along chromosome 4 of these species. From the 6 simple segmental lines and by means of a new crossing strategy, the 6 respective homozygous segmental hybrid offspring were obtained, each of them carrying a specific homozygous introgression. None of the 6 heterozygous introgressions was capable of producing sterility in segmental males, while 4 of the same homozygous introgressions produced total sterility in segmental males, including in this group the two smallest introgressive segments, one of 5.03 % and the other 7.87% with respect to the total length of chromosome 4, which are located in the region F2 to F4 of the standard cytological map based on polythene chromosomes of the Drosophila Repleta group. In situ hybridization, using 8 clones from contig 1065 located along the F2 to F4 region of the physical map of D. buzzattii constructed in BACs, confirmed the precise location of the 6 clones in the chromosomal region F2 to F4 of chromosome 4 of the polygenic chromosomes of both D. buzzatii and D. mojavensis. The bioinformatic analysis of the F2 to F4 region, using the complete genetic sequence of the contig 1065 of D. buzzatti shows the presence of two predicted genes in the genomic map of D. buzzatii (g.1313.t1 and g.1314.t1), and the orthologous association of these 2 genes both with the D. moj_GI22766 gene of D. mojavensis and with the Trivet gene of D. melanogaster.

Cytogenetic comparison of chironomid midge Glyptotendipes glaucus (Meigen, 1818) (Diptera, Chironomidae) populations from Northwest Russia and Ukraine (Chernobyl zone)

Functional characters of polythene chromosomes and chromosomal rearrangements in salivary glands of 177 larvae of Glyptotendipes glaucus (Diptera, Chironomidae) from reservoirs of Russia and Ukraine (Chernobyl) have been analysed. Similarity of the populations studied based on a pool of chromosomal reorganizations has been established. The general types of inversions in chromosomal arms A, B, D and E have been detected. Influence of radioactive pollution (Chernobyl) on functional changes of a nucleus, Balbiani rings, puffs, morphology of disks and interdisks is revealed.

Effects of microwaves on the puffing pattern of D. melanogaster

The influence of electromagnetic field exposure on puffing pattern of salivary gland polythene chromosomes, viability and fertility of Drosophila melanogaster of the wild type Canton-S line was studied. Experimental conditions: Electromagnetic field characteristics: frequency — 36.64 GHz, power density — 0.4 W/m2, exposure time −10 seconds. Electromagnetic field exposure was conducted on the egg stage. Results: in larvae developed from the exposed eggs 3 of 8 chromosomal puffs tested (71CE, 82EF, and 83E) had significantly smaller dimensions than these in control at the prepupal stage. Viability of Drosophila estimated by the number of adult flies hatched from exposed eggs decreased, while the number of dominant lethal mutations increased. Conclusion: the exposure to a low-level microwave irradiation suppressed puffing activity at ecdysone-inducible loci of Drosophila polythene chromosomes, increased frequency of dominant lethal mutations and decreased Drosophila viability but did not influence Drosophila fertility.

Protein synthesis in salivary glands of Drosophila hydei after experimental gene induction

Several treatments, namely incubation at 37 degrees C, in the presence of arsenite, 2,4-dinitrophenol or vitamin B-6, or release from anaerobiosis induce the same set of puffs in the polythene chromosomes of salivary glands of Drosophila hydei. Analysis of changes in protein-synthetic patterns (as determined by radioautography of sodium dodecyl sulphate-gel electrophoretograms of extracts from [35S]methionine-labelled salivary glands) showed that concomitant with puff induction by these various treatments the same six strongly labelled polypeptide bands appeared. The amount of radioactive label in these peptides accounted for 25% of the total incorporation of [35S]methionine, except during incubation at 37 degrees C when it accounted for about 50%. The rate of synthesis of these peptides was maximal 1 h after the start of the puff-inducing treatment. The rate of decay of the rate of synthesis showed first-order kinetics both after removal of the puff-inducing stimulus or in the presence of actinomycin, with a half-life of approx. 4h.