I-R hybrid dysgenesis in Drosophila melanogaster. Use of in situ hybridization to show the association of I factor DNA with induced sex-linked recessive lethals.

The purpose of this paper is the genetic visualization by in situ hybridization of 130 sex-linked recessive lethals plus a non-lethal induced by I-R dysgenesis. This collection of lethals involves inducer strains which differ in the position of the I elements on the X chromosomes. The I-R interaction was strong. Our previous results have shown that about 30% of the induced recessive lethals are associated with cytologically visible chromosomal rearrangements. (1) The rearrangements induced by I-R-type hybrid dysgenesis often exhibit homology with the I factor at the level of one or both junction points, depending on the types of chromosome rearrangements. These results suggest that the chromosome rearrangements arise directly from the transposition of I elements. However, the breakpoints of some types of cytologically non-visible deficiencies and of 2 small cytologically visible deficiencies do not present detectable homology with the I factor. (2) The majority of rearrangements do not involve the I elements already present on the paternal X chromosome. (3) The hybridization signal distributions on the X chromosome are not uniform. They present peaks of various heights which may correspond to specific anchoring areas of copies of I in the course of integration. (4) The data presented here agree with the literature with respect to the mean number of copies of I per X chromosome and to the excess of copies of I at locus 1A. Two rearrangement formation mechanisms are envisaged: crossing-over and 'target' exchanges.

I-R hybrid dysgenesis in Drosophila melanogaster: nature and site specificity of induced recessive lethals.

This paper presents results of the genetic and cytological analysis of 144 sex-linked recessive lethals, plus 1 non-lethal. All of them were induced by I-R hybrid dysgenesis. This collection of mutants was pooled from experiments involving inducer chromosomes that differ in the chromosomal position of their I elements. Our results show that 30% of the recessive lethals are associated with chromosomal rearrangements which depend on the strength of the I-R interaction. These lethals are induced on both inducer- and reactive-origin chromosomes, and their frequency is dependent on the structure of the inducer chromosome used. The I-R-induced lethals occur along the entire length of the X chromosome. These sites probably correspond to specific loci which are more or less homologous with I. The complementation relationships showed that some specific loci were more frequently involved in all the lethal mutations tested. The most sensitive loci are, in order of observation: l(1)J1, ct, f, ma1 and m. Among induced recessive lethals considered to be point mutation, complementation tests showed that many of them are in fact multilocus deficiencies which can be detected only at the molecular level. It seems that the production of I-R rearrangements (cytologically visible or not) may be the most important mechanism leading to lethal mutations. These mutations probably occur during the transposition of I elements, hence their importance from an evolutionary standpoint.

Some results of the effect of space flight factors on Drosophila melanogaster.

Two experiments with Drosophila melanogaster males were performed aboard the Salyut 6 orbital station. Mutagenic effects of a 8 day space flight on sex chromosome nondisjunction and intergene recombination in chromosome II were studied. The space flight factors (SFF) increased the frequency of chromosome nondisjunction and recombination. The model experiments showed that the combined effects of vibration and acceleration do not cover the whole spectrum of space flight mutagenic factors. These data suggest that heavy space ions are mainly responsible for the observed effect.

Hybrid dysgenesis in Drosophila melanogaster. I. Further evidence for and characterization of the mutator effect of the inducer-reactive interaction.

1. Several experiments were carried out to study, in the I-R hybrid dysgenesis system, the induction of recessive sex-linked lethal mutations in the progeny of SF females (obtained from crosses of female R by male I) or of RSF females (obtained from crosses of female I by male R). 2. Induced lethals were found in the progenies of SF females but not in those of RSF females. 3. The frequency of induced lethals decreased as SF females grew older. 4. A difference in the frequency of the induced lethals according to the reactive or inducer chromosome origin seemed apparent. Such frequency systematically appeared to be higher for the chromosomes of reactive origin. 5. The correlation between the rate of induced lethals and the intensity of the I-R interaction, as well as the characteristics of the lethals obtained and their non-random distribution, are in agreement with the hypothesis that the mutations are the consequence of the transposition of the I factor.

Variations in the recombination rate of Drosophila melanogaster induced by balloon flight.

Drosophila males, heterozygous for b, pr, cn and en genes, were submitted to balloon flights, ceiling time ranging from about 8 hours (flights performed in France) to 22 hours (transmediterranean flight). Effects on recombination were investigated on progeny after breeding with females homozygous for the same genes. The transmediterranean flight and one flight performed in France resulted in a significantly higher recombination rate.

Genetic effects of balloon flight in Drosophila melanogaster.

Drosophila males were flown in balloons and crossed, after recovery, in order to investigate possible genetic effects of cosmic rays. No significant effect was observed in the lethal and dominant mutation rate.