Genetical variation for enzyme activity in a population of Drosophila melanogaster. VI. Molecular variation in the control of alcohol dehydrogenase (ADH) activity

Structure, frequency and distribution of P elements in relation to P—M hybrid dysgenic male recombination inDrosophila melanogaster

The frequency and distribution of P elements were investigated in the third chromosomes of two wild-type strains ofDrosophila melanogasterusingin situhybridization of biotinylated probes to the polytene chromosomes. The relationship between these data and the extent of hybrid dysgenesis was determined through assays of egg production, egg hatchability (F2embryo lethality),snwdestabilization and male recombination along the third chromosome. The results suggest that P-element distribution, frequency and structure are all contributory factors in the regulation of hybrid dysgenesis. Texas 6 was shown consistently to be a stronger P strain than Texas 1, eliciting greater reductions in fertility, more extensivesnwdestabilization and higher frequencies of male recombination. Clustering of male recombination events, arising from pre-meiotic crossing over, was evident among the dysgenic progeny of each strain. Male recombination andsnwdestabilization were independently distributed among the dysgenic males studied, suggesting that these traits represent separate P-mediated functions. The third chromosome male recombination maps produced by the two strains differed significantly from each other and from the published female meiotic and polytene chromosome maps. Male recombination breakpoints were associated with the original distribution of P sequences in the two strains and the results suggest that this relationship may be closer for potentially complete P factors than for P sequences in general. An analysis of sub-lines derived from individual recombinant males revealed that chromosomal breakpoints could also be associated with novel insertions following P-element transposition.

Chromosome interactions in P-M dysgenic male recombination of Drosophila melanogaster

The frequency, distribution and structure of P elements on the second and third chromosomes of Texas 1, a wild-type inbred strain of Drosophila melanogaster, were investigated by in situ hybridization. These autosomes were isolated individually and used as P-element donors to study the frequency and distribution of male recombination events generated on recipient chromosomes which were originally devoid of P sequences. The P-element array of chromosome 2 was shown to generate higher male recombination frequencies on chromosome 3 than vice versa, despite having fewer P factors and fewer P elements in general. This is likely to be due to the presence and distribution of specific P-deletion derivatives, which vary in their ability to repress P mobility. The male recombination generated on recipient chromosomes is associated with the insertion of donated P sequences, but only in a small minority of cases could a novel P-element site be detected at, or near, the recombination breakpoint. The majority of such breakpoints appear to be associated either with unsuccessful P insertion, or with the action of P transposase attracted by P elements newly inserted elsewhere on the recipient chromosome. Recent evidence also suggests that a small proportion of the breakpoints may be associated with the action of P transposase alone. Male recombination breakpoints appear to be distributed effectively at random along the recipient autosomes, and their frequency of occurrence was shown to correlate with the physical length of DNA available between markers, as revealed by the polytene map distance.

Quantitative analysis of RNA produced by slow and fast alleles of Adh in Drosophila melanogaster

The alcohol dehydrogenase (ADH) locus (Adh) of Drosophila melanogaster in polymorphic on a world-wide basis for two allozymes, Fast and Slow. This study was undertaken to determine whether the well-established difference in ADH protein concentration between the allozymes is due to a difference in mRNA levels. RNA gel blot hybridization and an RNase protection assay were used to quantify ADH mRNA levels. Each method used an Adh null mutant as an internal standard. Several Slow and Fast allele pairs of different geographic origins were analyzed. The results provide strong evidence that the ADH protein concentration difference is not accounted for by RNA level.

Relation between tolerance to ethanol and alcohol dehydrogenase (ADH) activity in Drosophila melanogaster: selection, genotype and sex effects

The suggestion of Oakeshott et al. (1984) that selection at the Adh locus, as a response to ethanol, is restricted to D. melanogaster laboratory-adapted populations, is tested in this paper with the "Lagar de los Reyes" (LR) lines. For this purpose, homozygous lines for the AdhF and the AdhS alleles were maintained on food supplemented with ethanol. After the selection, the ethanol tolerance and the ADH activity of the selected flies (LRSeF and LRSeS) were determined and compared with those of the control flies (LRCF and LRCS), maintained on standard medium. Then, the effects of the selection, genotype and sex, and the relation between ethanol tolerance and ADH activity were analysed. Our results fail to show a consistent correlation between ethanol tolerance and ADH activity in the adults of LR lines. Our findings also indicate that adaptation of D. melanogaster to ethanol-containing food could be accomplished without significant changes on the ADH activity in the adults. The possibility that the adaptation of D. melanogaster to environmental ethanol could be independent of the Adh locus is discussed.

Restriction endonuclease map variation and gene activity in the Adh region in a population of Drosophila melanogaster

Variation within a 12 kb region containing the Adh gene was studied in 16 highly inbred lines of independent extraction from a population of Drosophila melanogaster, "Texas". Out of a selection of 8 hexanucleotide specific restriction endonucleases, four restriction site and five DNA insertion/deletion variations were observed and the heterozygosity per nucleotide was 0.004. Linkage disequilibrium between two restriction sites, considerably removed from and on either side of the Adh transcriptional unit, identified two major classes of chromosome or haplotype in the population. These two haplotypes were strongly associated with the capacity of lines to respond to the environment (genotype-environment interaction) in ADH activity. It was concluded that a control or regulatory polymorphism was present in the population in association with the Adh transcriptional unit.