Meiosis in Drosophila melanogaster

Chromosome pairing during meiosis I in D. melanogaster males was investigated ultrastructurally by examining complete bivalents in electron micrographs of serial thin sections. The XY bivalent is characterized by the presence of unique material located between the two half-bivalents at the site of synapsis. The material has a fibrillar appearance and is less electron dense than the surrounding chromatin. YY bivalents in XYY males and XY bivalents containing the X chromosome, In(1)sc ^4Lsc^8R, where the pairing sites of the X chromosome are inverted and partially deleted also possess this material. The material is not associated with autosomal bivalents and may represent a morphological manifestation of the hypothetical cohesive elements (collochores) which are thought to function in conjunction of the X and Y chromosomes (Cooper, 1964).     

Meiosis in Drosophila melanogaster

Individual bivalents or chromosomes have been identified in Drosophila melanogaster spermatocytes at metaphase I, anaphase I, metaphase II and anaphase II in electron micrographs of serial sections. Identification was based on a combination of chromosome volume analysis, bivalent topology, and kinetochore position. — Kinetochore microtubule numbers have been obtained for the identified chromosomes at all four meiotic stages. Average numbers in D. melanogaster are relatively low compared to reported numbers of other higher eukaryotes. There are no differences in kinetochore microtubule numbers within a stage despite a large (approximately tenfold) difference in chromosome volume between the largest and the smallest chromosome. A comparison between the two meiotic metaphases (metaphase I and metaphase II) reveals that metaphase I kinetochores possess twice as many microtubules as metaphase II kinetochores. — Other microtubules in addition to those that end on or penetrate the kinetochore are found in the vicinity of the kinetochore. These microtubules penetrate the chromosome rather than the kinetochore proper and are more numerous at metaphase I than at the other division stages.     

Selection and recombination in Drosophila melanogaster

Summary Artificial selection for wing length in Drosophila melanogaster resulted in changed crossing-over frequencies between three marker genes on the 2nd chromosome, b, cn and vg.The results suggest that artificial selection is a causal agent in producing the observed changes; moreover it is suggested that the modifications in cross-over frequency are controlled by extra-nuclear factors.Research supported by C.N.R. Consiglio Nazionale delle Ricerche Roma, Grant n. 115.2298.4791.     

Mutagenicity studies in Drosophila melanogaster with Lannate 20

Lannate 20 a carbamate pesticide was evaluated for its mutagenicity in Drosophila melanogaster by the sex-linked recessive lethals and chromosome II-III translocation tests by continuous larval feeding. The 3 sublethal doses of 0.2, 0.4 and 0.6 microliter of Lannate per 100 ml of the food medium induced a significant (P less than 0.01) increase in the number of sex-linked recessive lethals over the controls. However, no translocations were observed either in the treated or the control series.     

Synaptonemal polycomplexes in Drosophila melanogaster

Synaptonemal polycomplexes are described for the first time in Drosophila melanogaster females. They were found in apparently degenerating 16-cell clusters in germarial region two of females heterozygous for the c(3)G ¹⁷ mutation. The remaining 16-cell clusters in the germaria were normal in appearance. In a single case a polycomplex was found in the cytoplasm, presumably due to the breakdown of the nuclear envelope. In all other cases, the polycomplexes were closely associated with the nucleolus. The role of the nucleolus in the formation of polycomplexes as well as the possibility that these polycomplexes are normal features of the meiotic prophase in Drosophila are discussed.     

Competitive interactions in Drosophila melanogaster

A competition experiment with Drosophila melanogaster is reported which comprised a replacement series with two genotypes, together with pure cultures of both genotypes at the same densities as they appeared in the mixtures. The results for total numbers and weights make clear the need to separate the intergenotypic from the intragenotypic interactions if an unambiguous interpretation of the outcome of such mixtures is to be obtained. Further experiments were carried out to investigate the behaviour of pure cultures in order to gain insight into the relative simplicity or complexity of the intragenotypic interactions that needed to be taken into account when investigating mixtures. It was found that transformation of the measurements into percent survival and average weight per fly led to relations with density which were more nearly linear than the originals and, hence, were more readily amenable to analysis. Two main points emerged from the experiments. First, the relationship between the two transformed characters did not appear straightforward. Secondly, the intragenotypic interactions, particularly for percent survival, were complex and thus provided not support for assuming them to be simple when present in mixtures of genotypes.