Raphael Falk

Labellar taste organs of Drosophila melanogaster

There are 36 to 42 taste bristles on each half of the labellum of Drosophila melanogaster; most of them are two‐pronged with a pouch between them. Some end bluntly with a pore at the tip.

Fine structure analysis of a chromosome segment in Drosophila melanogaster: analysis of ethyl methanesulphonate-induced lethals.

Abstract An allelism matrix of ethyl methanesulphonate-induced recessive lethals found in a short chromosomal segment covered by the Y· mal + chromosome was constructed. When allelism tests for the lethals were extended to X-ray-induced lethals, a consistent linear map of 34 functional units could be constructed. 80% of the chemically induced lethals comprised single sections, which supports the view that most ethyl methanesulphonate-induced lethals were point-mutations. Most X-ray-induced lethals that were multi-section lethals were aberrations. The distribution of mutations in the affteced units was highly non-random; consequently any pooling of sensitivity patterns for whole chromosome segments would be misleading. There were some “hot-spots”, possibly due to the vicinity of intercalary heterochromatin. There was also an excess of chromosomes with more than one lethal. The possibility that variation in specificity of lethal and visible mutations obtained with different mutagenic agents is a secondary function of the number of “essential sites” in “vital” and “non-vital” genes is discussed.

Fine structure analysis of a chromosome segment in Drosophila melanogaster. Analysis of x-ray-induced lethals.

Abstract Allelism tests were performed between X-ray-induced lethals that were located on the X-chromosome of Drosophila at a region covered by the Y.ma-l + translocation. The complementation map which was constructed from the matrix of allelic combinations proved to be linear. So far 20 sections, or functional units, have been delineated. Further analysis should increase the number of sections until each section comprises one cistron. Practically all post-meiotic X-ray induced lethals in the region were aberrations. It is inferred that visible mutations induced by X-rays were deficiencies at non-essential loci. The breakage points of mutations in the segment were not distributed at random. The “hot spot” was attributed to an intercalary heterochromatic band, which by pairing with the adjacent proximal heterochromatin caused preference in breaks simultaneously at the “hot spot” and the proximal heterochromatin, and hence also caused preference for extensive aberrations. A correlation was found between male sterility and heterochromatic aberrations, but not between male sterility and X:A translocations. This kind of analysis suggests new approaches to the study of the organization of the genetic material in chromosomes and the nature of various mutational events.

A potential for learning probability in young children

Sixty-one children, from 4 to 11 years old, were presented with two sets, each containing blue and yellow elements. Each time, one colour was pointed out as the payoff colour (POC). The child had to choose the set from which he or she would draw at random a POC element in order to be rewarded. The sets were of varying sizes with different proportions of the two colours. The problem was to select the higher of the two probabilities. Three kinds of materials were used: Pairs of urns with blue and yellow beads, pairs of roulettes divided into blue and yellow sectors, and pairs of spinning tops, likewise divided into two colours.Roughly around the age of six, children started to select the greater of the two probabilities systematically. The dominant error was selecting the set with the greater number of POC elements. Verbal concepts of probability and chance were explored and some ‘egocentric’ thought processes were described. The study indicates that probability concepts could be introduced into school teaching even in the first grades. The deterministic orientation in the instruction for young ages should be attenuated, permitting concepts of uncertainty right from the beginning.

The gene in search of an identity.

SummaryThe concept of the difference between the potential for a trait and the trait proper, i.e., between the genotype and the phenotype, became clear only during the first decade of the century, mainly through the work of Johannsen. Although Johannsen insisted on that the terms he coined were only helpful devices to organize data about heredity, it is obvious that they were bound from the beginning to the hypothesis that there was “something” in the gametes that could be rendered to analysis as discrete units. These units were the genes.This reductionist yet materially non-committed attitude has been developed into what I called instrumental-reductionism: the genes were hypothetical constructs that were accepted “as if” they were real entities. The research program developed on such a concept was very successful, not least because this instrumental approach allowed maximum flexibility in the attachment of meaning of the genes. While most geneticists accepted one or another position of this flexible concept, others took more extreme positions. At the one extreme end of the conceptual continuum was the realist approach that argued that genes were discrete, measurable, material particles, and on the other end, the claim that the attempts to identify discrete units only led to hyperatomism of a holistic view appropriate to heredity.The acceptance of the gene as a material and discrete unit, in the beginning of 1950s, opened the way to a deeper level of conceptualizing both its structure (“cistron-recon-muton”) and function (“one gene—one enzyme”). The discovery of the structure of DNA finally offered a chemical-physical explanation to the geneticists requirements of a material gene. Thus, within less than 20 years the gene has been established as a “sharply limited segment of the linear structure” that is involved in the structrue of a product or its regulation.However, with turning of much of the attention to the eucaryotic DNA, it was necessary to accommodate the gene to an increasing flood of findings that did not tally with its concept as a discrete material unit. Without much heart-seeking among geneticists, the gene regained its role as an instrumental unit, or even as just an intervening variable, “a quantity obtained by specified manipulation of the values of empirical variables”. Though this flexibility demonstrated again that “the most fruitful concepts are those to which it is impossible to attach a well defined meaning”, it brought us also into a situation in which the same term has a different meaning for each group of scientists. In order to avoid the danger “to be scattered over the face of all the earth” because of lack of communicable language, it might be advisable to halt a little and reflect on the meaning of our concepts and their function.

Nitrogen-treatment effects on rearrangement-induction patterns in Drosophila melanogaster.

SummaryRecovered rates of Y-chromosome-autosomal translocations (Y-A) induced in spermatids of pupae of Drosophila melanogaster, as well as the chromosomes 2–3 translocations (2–3), were higher in crosses to females having an attached X.Y-chromosome than to regular females. This suggests that numerous position-effect sterility mutations were induced in the Y-chromosome as well as in the autosomes.Nitrogen treatment after irradiation of 800 r did not increase the frequencies of translocations recovered.Prolonged nitrogen pre-treatment apparently retarded development so that irradiation involved an earlier and more sensitive stage of spermiogenesis than without pre-treatment. The increase of the 2–3, was higher than that of the Y-A translocations, indicating a lower stage-sensitivity of the latter.When two irradiations were given 14 hours apart in air, breaks induced in the first irradiation rejoined prior to the second. Prolonged nitrogen treatment after the first irradiation caused a delay in rejoining of...

Taste responses of Drosophila melanogaster

Abstract The amounts of sugar solution consumed by Drosophila melanogaster flies were determined. Starved and desiccated flies of a wild type strain (QA) consume 7−9 × 10 −2 λ of a 0.3 M sucrose solution per fly during the first hour and less later. They consume more of the 0.3 M sucrose solution than of the more diluted and the more concentrated solutions. In preference-aversion tests the flies discriminated between water and various sugar solutions, and between different sugar concentrations. Contrary to other fly species these flies did not prefer 0.05 M fructose over 0.05 M glucose. 0.3–0.5 M NaCl added to 0.1 M sucrose turned a preference over 0.01 sucrose into an aversion. A mutant, Lot-94, selected for its increased consumption of a 1 M NaCl solution was found to consume more of all test solutions. The amount of NaCl that had to be added to 0.1 M sucrose to turn the preference over 0.01 M sucrose by the mutant flies into aversion was not different from that found for the wild type flies.

The real objective of Mendel's paper: A response to Monaghan and Corcos

Mendels work in hybridization is ipso facto a study in inheritance. He is explicit in his interest to formulate universal generalizations, and at least in the case of the independent segregation of traits, he formulated his conclusions in the form of a law. Mendel did not discern, however, the inheritance of traits from that of the potential for traits. Choosing to study discrete non-overlapping traits, this did not hamper his efforts.

Temperature-sensitive prune (pn) mutations of Drosophila melanogaster.

Temperature-sensitive mutations, at the prune locus (pnts) of Drosophilia melanogaster, were induced with EMS. The majority of the new class of mutations, designated pnts-e, do not interact with the mutation Killer of prune (Kpn) at all of the experimental temperatures, i.e., pnts-e, Kpn flies do not die. One mutation, designated pnts-ek, is temperature-senstive with respect to both the eye coloration and the interaction with Kpn. pntr (temperature-non-sensitive), pnts-e, and pnts-ek alleles were found to differ with respect to both quantity of drosopterines and the color of the eyes. The temperature-sensitive period (TSP) for pn eye color occurs at a late pupal stage. The TSP for the pn--Kpn interaction lasts from the beginning of the first laraval instar to eclosion [22]. It is concluded that all pn mutations known to date occupy the same functional unit. The various pn mutations affect the same metabolic step to various degrees: the eye color phenotype results from a reduction in the end product, while the interaction with Kpn depends on the amount of the accumulated precursor. No recombination between pn alleles was found among more than 106 zygotes that were scored. The reasons for this failure are discussed.

Linkage: from particulate to interactive genetics.

Genetics was established on a strictparticulate conception of heredity. Geneticlinkage, the deviation from independentsegregation of Mendelian factors, was conceivedas a function of the material allocation of thefactors to the chromosomes, rather than to themultiple effects (pleiotropy) of discretefactors. Although linkage maps wereabstractions they provided strong support forthe chromosomal theory of inheritance. DirectCytogenetic evidence was scarce until X-rayinduced major chromosomal rearrangementsallowed direct correlation of genetic andcytological rearrangements. Only with thediscovery of the polytenic giant chromosomes inDrosophila larvae in the 1930s were thevirtual maps backed up by physical maps of thegenetic loci. Genetic linkage became a pivotalexperimental tool for the examination of theintegration of genetic functions in developmentand in evolution. Genetic mapping has remaineda hallmark of genetic analysis. The location ofgenes in DNA is a modern extension of thenotion of genetic linkage.