Influencing the spontaneous and chemically induced mutability of E. coli through changing the genetic background

Summary The influence of a second auxotrophic marker to the spontaneous and chemical-induced mutability to prototrophy of a first auxotrophic marker in 7 monoauxotrophs and 31 biauxotrophs of E. coli K 12 was studied by growth layer technics. No case of influence of a second auxotrophy to the mutagen-induced mutability (7 mutagens tested) of the first auxotrophy among 172 possibilities was found. An influence to the spontaneous mutability seemed to be present in 4 cases out of 31. But 3 of them were shown to be imitated by influences of components of the medium to the growth of mutants or parent type. In one case a mutator mutation is responsible for the about 8 times higher rate of the mutation met 1+ in strain met 1/his 7 than in strain met 1. But backmutation and crossing experiments showed that the mutator (mum ⁺) was separate from the auxotrophic marker his 7 (recombination frequency 5/16). This mutator did not increase remarkably the spontaneous mutability of other markers tested (resistence to phages T1 or T4 or to Streptomycin 3, 5, 10, or 100 /ml, or to Chloramphenicol 2 /ml). It is assumed that the spontaneous mutations in the wild-type are at least partially different in their nature from the mutator promoted ones.     

Heat shock induced phenocopies of dominant mutants of the bithorax complex in Drosophila melanogaster.

Summary Heat shock of 37°C applied to Drosophila embryos at blastoderm stage induces phenocopies of some dominant mutants of the bithorax complex. Heat shock might shut down functions of cis regulator genes involved in embryonic pattern formation.     

Comparison of types of chemically induced genetic changes in mammals

The present paper reviews the currently available in vivo systems for detection of chemically induced mutations and chromosome aberrations and summarizes the data of the relevant tests for mammalian germ-cell mutations (specific-locus test and heritable translocation test). The value of in vivo screening tests (somatic mutations and sperm abnormalities) for predicting specific-locus mutations is illustrated by comparing doubling doses. The results from the mammalian germ-cell mutation tests (specific-locus test and heritable translocation test) constitute the base-line for an assessment of predictability. Radiation and chemically induced specific-locus mutations differ in a number of respects, suggesting a need for caution in making risk estimates for chemical mutagen exposures in terms of radiation-equivalent doses. In vivo nondisjunction tests are discussed. Finally, unsolved problems and difficulties in generalizing qualitative and quantitative correlations between test systems are outlined. It is concluded that even qualitative predictions from data on somatic cells to germ cells are at best insecure because germ-cell specificity cannot be foretold, not to mention the fact that quantitative extrapolations from the results of in vivo screening tests, in general, are fraught with even more uncertainties. There is an acute need for collection of more data from studies involving germ cells.     

A Wolbachia-associated fitness benefit depends on genetic background in Drosophila simulans

The alpha-proteobacteria Wolbachia infect a number of insect species and influence host reproduction to favour the spread of infected females through a population. The fitness effect of this infection is important in understanding the spread and maintenance of Wolbachia within and among host populations. However, a full elucidation of fitness effect requires careful control of host genetic background. Here, I transferred a single clone of Wolbachia (the wHa strain) into three genetically distinct isofemale lines of the fly Drosophila simulans using microinjection methodology. These lines carried one of the three described mitochondrial haplogroups (siI, siII or siIII) and differ in nuclear genome as well. Population cage assays showed that wHa-infected siIII flies enjoyed a dramatic fitness benefit compared to uninfected siIII. In contrast, wHa did not affect the fitness of siI or siII flies. This study points to the importance of host-by-symbiont interaction terms that may play an important role in organismal-fitness.     

Genetic tests for the detection of chemically induced small deletions in Drosophila chromosomes

We have developed genetic tests for estimating the proportion of small deletions among chemically induced point mutations in Drosophila. The criteria used allow the detection of deletions that are large enough to include a viable visible mutation as well as a lethal, or a sex-linked lethal as well as a gene that is required for the development of a spermatogonium into a spermatozoon. On these criteria, we have concluded that DEB produces a high proportion of deletions among point mutations; that HA produces no deletions; and that DEN produces either no deletions or only very small ones that cannot be detected by our methods.     

The yellow condition in Drosophila melanogaster. A biological structuralist approach to the study of phenocopies

A phenocopy, as defined by Goldschmidt, is an environmentally induced form which resembles a genetic mutant. They have a site of induction at a number of developmental levels and are not only produced by interfering with gene gene expression. Phenocopies and the corresponding genetic mutant, are also not necessarily generated through equivalent developmental pathways. The yellow phenocopy of Drosophila melanogaster, where both cuticle colour and mating behaviour resembles that of the yellow mutant, serves to illustrate the above points. It is suggested that if the term phenocopy is to be used the term should correspond to the generative processes and hence transformations which mutant and phenocopy share, rather than purely on phenotype. Finally, phenocopies are discussed in relation to structuralist biology, showing how they are instructive in describing generative processes, sensitive periods in development and differing modes of inheritance in such a research programme.     

The genetic effects induced by an irradiation in low doses at Drosophila melanogaster

This article generalizes the results received by authors in researches of genetic effects of an irradiation for Drosophila. It is supposed, that the main effect of low intensity irradiation is connected with the induced genetic instability on which background the realization of effects of a different direction is possible.     

Evaluation of genetic damage induced by 8-ethoxycaffeine in Drosophila melanogaster

The methylated oxypurine, 8-ethoxycaffeine (EOC), was tested for the induction of genetic damage in Drosophila melanogaster. Sex-linked recessive lethals, sex-chromosome loss and tanslocation induction were studied following treatment of adult males, using a feeding technique. Our results show that EOC induces sex-chromosome loss and translocations between the second and third chromosomes, but is unable to induce point mutations in male germ cells under our conditions of testing.     

Gene instability induced by mobile genetic elements in Drosophila melanogaster]

The genetic instability of Drosophila melanogaster genes induced by the mobile genetic elements is reviewed. The main attention is paid to genetic instability depended on types of crossing. Data on the possibility of genetic instability induction by the chemical and physical (X-rays, heat-shock) agents and their complex effect are cited. It was shown that a number of agents which cause mutagenic effect realize their action by involving of mobile genetic elements.     

Problems of studying the genetic background of speciation as examplified by Drosophila virilis group

Possible ways of studying the genetic bases of speciation have been shown on the example of published data and authors' results. The data were used, which were obtained on different Drosophila species. Possible application of mapping by localization of the gene of quantitative traits and genetic transformation for solution of the problems of speciation is discussed.