bluuebunny/crossref_metadata_2025_split huggingface dataset:
exrB: amalB-linked gene inEscherichia coliB involved in sensitivity to radiation and filament formation
Authors: Greenberg Joseph , Berends Leonard J. , Donch John , Green Michael H. L. 
Published: September 2009

SUMMARYPAM 26, a radiation-sensitive mutant ofEscherichia colistrain B, is described. Its properties are attributable to a mutation in a gene,exrB, which is cotransducible withmalB. It differs fromuvrA(alsomalB-linked) derivatives of strain B in being sensitive to 1-methyl-3-nitro-1-nitroso-guanidine and γ-radiation, and in being able to reactivate UV-irradiated phage T3. It differs fromexrA(alsomalB-linked) derivatives of strain B in forming filaments during the course of normal growth as well as after irradiation. WhenexrBwas transduced into a K12 (lon+) strain, filaments did not form spontaneously. Three-point transductions established the order of markers asmet A malB exrB. Based on an analysis of the frequency of wild-type recombinants in a reciprocal transduction betweenexrAandexrBstrains, it was inferred that they are not isogenic and that the order of markers ismalB exrA exrB.
Detrimental genes with partial selfing and effects on a neutral locus
Authors: Ohta Tomoko , Cockerham C. Clark 
Published: September 2009

SUMMARYGene and genotypic frequencies for a deleterious mutant in mutation selection balance are derived for an infinite population undergoing partial self-fertilization. These provide formulations of mean survival and the mutational load. Obtained also are the average number of mutant genes and affected individuals stemming from a single mutant.As a concomitant effect on frequencies at a neutral locus the mutational load is distributed disproportionately among the neutral genotypes. For partially recessive mutant genes on the 1, 1-sh, 1-sscale, the effect is to increase the frequency of the heterozygote and to decrease the frequencies of homozygotes at the neutral locus relative to the frequencies expected with complete neutrality. This apparent overdominance at the neutral locus has been shown to be connected with identity disequilibrium rather than linkage disequilibrium. It increases generally assandhdecrease, and as the proportion of self-fertilization and the degree of linkage increase. The apparent overdominance with complete linkage is generally less than double that for free recombination. For partially dominant mutant genes,h≥ ½, the effects on the frequencies of heterozygote and homozygotes at the neutral locus are reversed.
Mitochondrial mutations affecting resistance to erythromycin and mikamycin inParamecium aurelia: provisional results with a new method
Authors: Queiroz Clara , Beale G. H. 
Published: September 2009

SUMMARYA new method for obtaining mitochondrial mutants ofParamecium aureliais described. Sensitive organisms were first placed in medium containing a low concentration (0·02 mg/ml) of erythromycin (ERY), insufficient to prevent fission. The paramecia were then transferred through a graded series of increasing ERY concentrations, with a period of growth at each concentration. A high yield of ERY-resistant mutants was obtained.Continuous growth in 0·02 mg/ml ERY also resulted in the accumulation of a spectrum of mutants resistant to various concentrations of ERY. Many of these mutants are also resistant to mikamycin. On returning the resistant paramecia to media lacking ERY, some clones remained resistant whilst others reverted to sensitivity.
Inversion polymorphism in a two-locus genetic system
Authors: Charlesworth Brian 
Published: September 2009

SUMMARYThe types of equilibria possible with an inversion in a two-locus system are considered, and their stability properties investigated. With complete suppression of crossing-over in inversion heterozygotes, there are three possible types of stable equilibria; which of these is reached by a new inversion depends on the fitness effects of the two loci concerned. With one of these equilibria, basically involving cumulative overdominance of the selected loci, the inverted and standard sequences are genetically homogeneous and differ with respect to both loci. With the other types of equilibrium, the standard sequence remains heterogeneous for one or both loci. It is shown that this situation may lead to variations in karyotypic fitnesses when the inversion is changing in frequency. It is also found that, with certain fitness relationships, two alternative stable equilibria may coexist; the final frequency reached by an inversion may therefore depend on the population's history.The effects of double crossing-over in inversion heterozygotes were also investigated, and it was shown that the equilibria with double crossing-over are closely related to the corresponding equilibria without it, except that both sequences are more heterogeneous genetically. Within each sequence there is almost complete linkage equilibrium between the selected loci, although both are in linkage disequilibrium with the inversion itself. It was also found that, with double crossing-over, the population tends to remain for many thousands of generations in a state of quasi-equilibrium. In this state, the inversion tends not to return to its original frequency after a perturbation; also, it may remain for a long time relatively homogeneous genetically, especially when rare.These results were compared with those from experiments and observations on inversion polymorphisms.
Position effect variegation in the mouse
Authors: Cattanach Bruce M. 
Published: September 2009

SUMMARYPosition effect variegation has been studied in female mice heterozygous for thefleckedX-autosome translocation, T(7;X)Ct. Some of these carried the spotting gene (s) which clarifies the variegated patterns. Others carried a second X-autosome translocation, T(X; 16)16H, which suppresses the randomness of X-chromosome activity.It was found the position effect variegation stems primarily from early occurring events which lead to the formation of clones of cells with different phenotypes. In this respect the phenomenon appears to parallel that found inDrosophila. However, in the mouse, late-occurring events are also found which can only be readily accounted for by the reactivation of previously inactive loci. They occur, not only during foetal development, but throughout the life-time of the animals and in a manner which suggests they derive from a progressive retreat of the inactivating influence of the heterochromaticXchromosome back along the attached autosome towards the breakpoint. It is proposed that the early occurring events do not lay down fixed programmes of gene suppression, as proposed forDrosophila, but that, like the later-occurring events, they represent the reactivation of previously inactivated loci. The possibility that this might also be true forDrosophilais discussed.The study also provided evidence favouring the view that theX-chromosome controlling element, Xce, modifies the heterozygous phenotypes ofX-linked genes by biasing the randomness of the X-inactivation process, rather than by operating through cell selection mechanisms. The data also support and extend Mintz's (1967) concept of pigment pattern differentiation.
The effects of mutantp-alleles on the reproductive system in mice
Authors: Melvold Roger W. 
Published: September 2009

SUMMARYThep6H,p25H, andpbsalleles at the pink-eyed dilution locus in mice (Mus musculus) cause sterility in males and semi-fertility in females when homozygous, while thepd, pun, p, and + alleles do not reduce fertility. Pituitaries from sterile males had significantly lower proportions of gonadotropic cells than pituitaries from fertile males. Ovaries from semi-fertile females contained large numbers of developing follicles, but no corpora lutea or corpora hemorrhagica were found. The proportion of polyovular follicles in ovaries of semifertile females was abnormally high.Pituitary gonadotropins appear to be reduced in the sterile genotypes although the lesion cannot be localized. Possible relationships between these and other pleiotropic effects of mutantp-alleles are discussed.
The use of bacteriophages for differentiating plasmids ofPseudomonas aeruginosa
Authors: Krishnapillai V. 
Published: September 2009

SUMMARYSix bacteriophages have been used in the classification of 19 plasmids (antibiotic resistance-mediating R factors and FP sex factors which promote host chromosome transfer) ofP. aeruginosaisolated in different geographical regions. On the basis of phage-plating responses on isogenic strains of bacteria differing only in the plasmids carried, five groups of plasmids were distinguishable. In general the groups could be correlated with their geographical origin although differences between plasmids from the same region were found. The unique phage-plating responses were also useful in establishing the possible identity of plasmids isolated from the same original strain and given different designations by independent investigators. The classification of the plasmids derived here on the basis of phage-plating responses could be correlated with classifications based upon other phenotypic characteristics described elsewhere. The nature of inhibition of plating of phages B39 and G101 by R18–1 and R18–3 respectively was shown to be due to interference with some aspect of intra-cellular phage replication rather than to plasmid-mediated restriction.
Cytogenetic and complementation analyses of recessive lethal mutations induced in theXchromosome ofDrosophilaby three alkylating agents
Authors: Lim J. K. , Snyder L. A. 
Published: September 2009

SUMMARYSalivary-gland chromosomes of 54 methyl methanesulphonate- and 50 triethylene melamine-inducedX-chromosome recessive lethals inDrosophila melanogasterwere analysed. Two of the lethals induced by the mono-functional agent and 11 of those induced by the polyfunctional agent were found to be associated with detectable aberrations. A complementation analysis was also done on 82 ethyl methanesulphonate- and 34 triethylene melamine-induced recessive lethals in thezeste-whiteregion of theXchromosome. The EMS-induced lethals were found to represent lesions affecting only single cistrons. Each of the 14 cistrons in the region known to mutate to a lethal state was represented by mutant alleles, but in widely different frequencies. Seven of the TEM-induced lethals were associated with deletions, only one of which had both breakpoints within the mapped region. Twenty-six of the 27 mutations in which only single cistrons were affected were mapped to 7 of the 14 known loci. One TEM- and two EMS-induced mutations were alleles representing a previously undetected locus in thezeste-whiteregion.
Bare-patches, a new sex-linked gene in the mouse, associated with a high production ofXOfemales: II. Investigations into the nature and mechanism of theXOproduction
Authors: Phillips Rita J. S. , Kaufman M. H. 
Published: September 2009

SUMMARYThe highXOproduction inBpa+ mouse stocks appears to be due, not toBpaitself, but to a closely linked factor for highXOproduction (Fxo) which may be a gene or a chromosomal aberration. The change ofBpa FxotoBpanon-Fxooccurs with a frequency of about 6%; the reciprocal change fromBpa FxotoFxonon-Bpahas not been found. There is some evidence thatFxomight involve a structural alteration such as an inversion or a deletion. TheX-chromosome loss is due to non-disjunction which occurs in about one-third of the oocytes, probably mainly at meiosis I. Frequencies of other chromosomal abnormalities found in the stocks are given.
Mitochondrial genetics, circular DNA and the mechanism of thepetitemutation in yeast
Authors: Clark-Walker G. D. , Gabor Miklos George L. 
Published: September 2009

SUMMARYWe propose a general hypothesis involving properties of circular DNA which can explain such phenomena as thepetitemutation, suppressiveness, and the polarity observed in mitochondrial recombination in the yeastSaccharomyces cerevisiae. This hypothesis involves excision and insertion events between circular DNA molecules as well as structural rearrangements in the DNA generated by these events. The special properties of circular DNA have been considered in analysing recombination, and a number of results are obtained which are not intuitively apparent.This hypothesis can be applied to any situation involving circular DNA such as bacterial plasmids and cytoplasmic circular DNAs, where the opportunity exists for recombination and rearrangement events.
Interactions between the surface exclusion systems of some F-like plasmids
Authors: Willetts Neil , Maule John 
Published: September 2009

SUMMARYFour surface exclusion systems have been identified amongst a group of F-like plasmids inE. coli: SfxI(F), SfxII(ColV2 and R538-1fin−), SfxIII(ColVBtrpand R1-19) and SfxIV(R100-1 and R136fin−). None of these systems was expressed in stationary phase cells or, except for ColVBtrp, duringfin+transfer inhibition, showing that the surface exclusion gene(s) is usually co-controlled with the transfer genes.Recipient cells carrying two plasmids specifying different surface exclusion systems did not always express both of these: the overall pattern suggested that the four systems and/or their sites of action are related. There was no surface exclusion between donor cells carrying two plasmids determining different surface exclusion systems and recipient cells carrying a plasmid determining either one of these. Our hypothesis to explain this and other results is that surface exclusion prevents interaction between the tip of the pilus on the donor cell and a receptor site on the recipient cell surface. Pili (probably mixed) with two types of tips would be present on cells carrying two different plasmids, the one unresponsive to the single surface exclusion system of the recipient cells allowing transfer of both plasmids.
A genetic study of female sterility inNeurospora crassa
Authors: Mylyk Orest M. , Threlkeld S. F. H. 
Published: September 2009

SUMMARYA genetic analysis following the initial detection of a female sterile variant resulted in the finding of seven or eight different female sterile mutants, most or all of which are on linkage groups I and II. They were present in heterokaryotic condition in already existing strains, except one which originated spontaneously during the study. All mutants fail to produce functional protoperithecia. Most of them, however, are able to function as female parents in heterokaryons. All mutants differ morphologically from the wild type, most being subtly different, but two being appreciably different. The apparently high frequency of occurrence of female sterile mutants suggests that protoperithecial development is under an elaborate genetic control. Differences in vegetative morphology appear to be a common property of mutants affecting the early stages of the sexual development.
Population structure in artificial selection: studies with Drosophila melanogaster
Authors: Madalena F. E. , Robertson Alan 
Published: September 2009

SUMMARYThe effect of sub-dividing a population during selection was studied by selecting downwards for sternopleural bristles in Drosophila melanogaster. The four structures used all involved the selection of 40 individuals out of 200 measured in each sex. The alternatives were:(i) one large line with the same selection procedure in all generations,(ii) eight small lines with the same procedure in all generations,(iii) the ‘single cycle’ structure in which large lines derived from crosses between selected small lines at either the sixth or twelth generation, and,(iv) the ‘repeated cycle’ structure in which the best five small lines were mixed at the sixth generation of selection to produce a new set of small lines on which the procedure was repeated for a total of three cycles.Of the first two methods, the large line had a higher final response than did any of the small lines. The latter, selected with an intensity of 5 out of 25 in each sex, had lower average final response than had a similar group of lines selected from the same base population with the lower intensity of 10/25. The results showed no clear effect of the sub-dicision of the population, followed by selection between lines, though they were in general agreement with theortical expectations. Several second chromosome recessive lethals were found at high frequencies in different selected lines. One of these, found in eight of the lines, had an effect on bristles in the heterzygote of about 1·5 phenotypic standard deviations. The evidence strongly suggests a pleiotropic effect on bristle score.
Genetic analysis of larval feeding behaviour inDrosophila melanogaster
Authors: Sewell David , Burnet Barrie , Connolly Kevin 
Published: September 2009

SUMMARYThe larvae ofDrosophila melanogasterfeed continuously during their period of development. The rate of feeding activity, measured as the number of cephalopharyngeal retractions per minute, varies with the physiological age of the larva. Feeding rate responded readily to directional selection to give rise to non-overlapping populations with fast and slow feeding larvae, respectively. Realized heritabilities for the character from different selected lines varied between 11 and 21%. Crosses between the selected populations show significant dominance for fast feeding rate and appreciable non-allelic gene interaction. Larvae of the slow feeding populations showed a correlated reduction in locomotor activity but fast feeding larvae do not move about significantly faster than the unselected controls. Asymmetry of the correlated response to selection, it is argued, is due to selection in the slow feeding populations of alleles with a secondary effect in both behaviours.
Genetic studies on male sterility of hybrids between laboratory and wild mice (Mus musculusL.)
Authors: Forejt J. , Iványi P. 
Published: September 2009

SUMMARYThe genetic control of the sterility of male hybrids between certain laboratory and wild mice (Mus musculusL.) is investigated. The observed sterility is, by definition, hybrid sterility since both parental forms (i.e. wild and laboratory mice) are fully fertile, their male offspring displaying small testes with arrest of spermatogenesis at the stage of spermatogenesis or primary spermatocytes. Results of genetic analysis as well as the failure to detect any chromosomal rearrangements point to a genie rather than a chromosomal type of hybrid sterility.Fifty-three wild males were classified into three sets, after mating with C57BL/10 inbred females, according to the fertility of their male progeny (set I – only sterile sons; set II – only fertile sons; set III – both fertile and sterile sons). The wild males of set I, which yield only sterile male offspring with C57BL/10 females, sire sterile sons also with females of the following inbred strains: A/Ph, BALB/c, DBA/1, and AKR/J, whereas the same wild males produce fertile offspring with females of C3H/Di, CBA/J, P/J, I/St and F/St inbred strains.The described hybrid sterility seems to be under the control of several independently segregating genes, one of them (proposed symbol Hst-1) being localized on chromosome 17 (linkage group IX), 6 cM distally from dominantT(Brachyury). A chance to search for the mechanism of hybrid sterility is provided by the finding of two laboratory inbred strains, C57BL/10 and C3H/Di, differing with respect to theHybrid sterilitygenetic system only at theHst-1 gene.Hst-1 is closely linked but apparently not identical with the sterility factor of recessive t alleles of theTlocus.
Further observations on the hairpin-tail (Thp) mutation in the mouse
Authors: Johnson D. R. 
Published: September 2009

SUMMARYThe hairpin-tail allele (Thp) of brachyury (T) on chromosome 17 of the mouse is unique in that the phenotype of heterozygous offspring depends on which parent contributed theThp.The present paper offers formal proof of this fact using theth2allele ofTas a marker, and discusses possible modes of action of the hairpin allele.
Physiological genetics of melanotic tumours inDrosophila melanogaster: VIII. The role of choline in the expression of the tumour genetu bwand of its suppressor,su-tu
Authors: Sparrow John C. , Sang James H. 
Published: September 2009

SUMMARYThe melanotic tumour genetu bwofDrosophila melanogasterhas a specific suppressorsu-tu. The genotypestu bw; +su-tuandtu bw; su-tushow opposite responses, as measured by tumour penetrance, to increasing choline levels in the defined axenic medium. The three major metabolic functions of choline have been examined using additions to the axenic medium to determine which biochemical pathway(s) are different in the two genotypes. It is concluded that the opposite strain responses are due to changes in the pattern of phospholipid synthesis, and that the gene product of thesu-tugene probably functions in this area of metabolism.
Aberrant ascus genotypes from crosses involving mutants at theglocus inSordaria fimicola
Authors: Kitani Y. , Whitehouse H. L. K. 
Published: September 2009

SUMMARYThe genotypes are given of over 4500 asci showing aberrant segregation at the grey (g) spore colour locus inSordaria fimicolafrom crosses, with outside markers present, betweenglocus mutants and wild type, or involving pairs ofglocus mutants that differed in spore colour (glocus mutants range from grey to hyaline). This colour difference enabled asci with aberrant segregation of the mutant spore colours to be detected in the two-point crosses, as well as those with wild-type (black) spores. From a total of 21 one-point crosses involving altogether seven primary and two secondaryglocus mutants, 2700 aberrant asci have been grouped into the 14 ascus genotypes that can be recognized, and in the two-point crosses 1830 asci (1044 fully scored) from 10 pairwise combinations of the mutants have been classified into the 150 ascus genotypes that can be distinguished.
The induction of ouabain-resistant mutants by N-methyl-N′-nitro-N-nitrosoguanidine in Chinese hamster cells
Authors: Davies Peter J. , Parry Jim 
Published: September 2009

SUMMARYClones of V79 Chinese hamster cells resistant to the steroid compound ouabain have been induced by mutagen treatment with MNNG (= N-methyl-N′-nitro-N-nitrosoguanidine). The frequency of resistant colonies was increased from spontaneous value of 2 × 10−6 to a frequency of 1·2 × 10−3 with MNNG treatment.The highest number of induced mutants appeared when an expression time pf 40 h was allowed between MNNG treatment and addition of ouabain.
Footpad bristles: a convenient metric character in mice
Authors: Festing Michael F. W. 
Published: September 2009

SUMMARYA new metric character in mice, ‘footpad bristle number’ is described. The character is easily measured under a stereo-microscope, is very highly inherited, and is independent of age, sex and the environment common to littermates. Such a character might prove useful in a number of quantitative genetic studies in mice.
Phenotypic characterization of R-factor tetracycline resistance determinants
Authors: Foster T. J. , Walsh Áine 
Published: September 2009

SUMMARYThe tetracycline-resistance determinants of R-factors from different compatibility groups have been tested inEscherichia coliK12 and phenotypically classified into two major classes. Class I determinants confer high-level resistance to tetracycline (> 100 μg/ml) and moderate resistance to minocycline (5–25 μg/ml) while those of Class II gave moderate resistance to tetracycline (50–70 μg/ml) and low resistance to minocycline. Each class was subdivided because of variation in resistance profiles and in the abilities of tetracycline and minocycline to induce increased resistance. Strains carrying two compatible TetrR-factors of the same or different phenotypic groups did not show increased tetracycline resistance.