bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phenotypic properties of R factors ofPseudomonas aeruginosa:R factors readily transferable betweenPseudomonasand the Enterobacteriaceae
Authors: Chandler P. M. , Krishnapillai V. 
Published: September 2009

SUMMARYR factors have been demonstrated in multiply drug resistant strains of enterobacteria andPseudomonas aeruginosain a Birmingham hospital (Lowburyet al.1969; Ingram, Richmond & Sykes, 1973). A comparative genetic analysis of these R factors has been initiated on the basis of a variety of phenotypic characteristics. This paper describes the properties of R factors derived from strains which could transfer multiple drug resistance to the recipient speciesP. aeruginosa, Escherichia coli, Shigella flexneriandSalmonella typhimurium. Two types of R factor could be recognized phenotypically. The single group 1 R factor, R18–1 which is probably the same as RPl-1 (Ingramet al.1972) was different to the group 2 R factors in many respects, including host range, R factor-specific phage plating, cellular location, drug resistance pattern, and stability. The group 2 R factors were found to be very similar to RPl (Grinstedet al.1972) and R1822 (Olsen & Shipley, 1973) with respect to their wide host range, plating of a sex specific phage, extrachromosomal location, and drug resistance pattern. Compatibility was shown between the group 1 R factor and a group 2 R factor, providing additional evidence for significant genetic differences.
Phenotypic properties of R factors ofPseudomonas aeruginosa:R factors transferable only inPseudomonas aeruginosa
Authors: Chandler P. M. , Krishnapillai V. 
Published: September 2009

SUMMARYA study was made of the R factors from two multiply drug resistant wild type isolates ofPseudomonas aeruginosafrom a Birmingham hospital (Lowburyet al.1969) from which, in contrast to other strains from the same source (Chandler & Krishnapillai, 1974a), drug resistance was not transferable toEscherichia coliK12 orSalmonella typhimurium. Transfer of drug resistance occurred at a low frequency toShigella flexneri, although drug resistance in this species was subsequently non-transferable.InP. aeruginosathere are several features of these two R factors which distinguish them from the group 1 and 2 R factors described previously (Chandler & Krishnapillai, 1974a). Although coding for resistance to neomycin and tetracycline, they did not express this resistance in two strains ofP. aeruginosaexamined, in contrast to the wild type strains they were isolated in.The control of transfer of the two R factors is different to the group 1 and 2 R factors in that derepression of transfer could be demonstrated following physiological treatments or mutagenesis. The R factors of this third group were compatible with the group 2 R factors, but did not repress their pilus synthesis on the basis of R factor specific phage plating.
Linkage disequilibrium and genetic variability
Authors: Bulmer M. G. 
Published: September 2009

SUMMARYIt has been shown previously that, even in the absence of linkage, selection can cause an appreciable change in the genetic variance of a metric character due to disequilibrium; this change is temporary and is rapidly reversed when selection ceases. This result is here extended to allow for the effect of linkage, and it is shown that the change in the variance is effectively determined by the harmonic mean of the recombination fractions. The validity of the approximate general formula derived here has been checked by comparison with exact results obtained from models with five or six loci. In order to determine the likely value of the harmonic mean recombination fraction, a simple model was constructed in which it was assumed that loci are distributed at random along the chromosome maps. Results of computer simulations of this model are reported for different chromosome numbers and numbers of loci.
Chromosome banding patterns and the origin of the B genome in wheat
Authors: Natarajan A. T. , Sarma N. P. 
Published: September 2009

SUMMARYThe distribution of heterochromatic regions in the chromosomes of diploid, tetraploid and hexaploid wheat shows that the B genome possesses characteristic large blocks. Though analyses of probable B genome donors indicate thatAegilops speltoideshas a pattern of distribution of heterochromatin nearest to the B genome chromosomes, a polyphyletic origin of tetraploid wheat seems more plausible.
Methods for the isolation and analysis of plasmodial mutants inPhysarum polycephalum
Authors: Cooke D. J. , Dee Jennifer 
Published: September 2009

SUMMARYAmoebae of the Colonia isolate ofPhysarum polycephalumproduce plasmodia within individual amoebal clones.This paper reports the derivation from the Colonia strainC50 of a strainCL(Colonia Leicester) which produces plasmodia in clones with high efficiency and which completes the life cycle reliably and repeatedly in single clones. The derivation of a lineCLd (CLdelayed plasmodium formation) is described and, usingCLd, the construction of the isogenic heterothallic strainsmt1;CLandmt2;CL.The above strains provide a system for the isolation and genetic analysis of mutants ofP. polycephalumwithin a uniform genetic background, in particular mutants expressed in the plasmodium.Using this system two auxotrophic mutants have been isolated. Preliminary genetic analysis has shown that they are due to single gene mutations.
Resistance to amino acid analogues inCoprinus: Dominance modifier genes and dominance reversal in dikaryons and diploids
Authors: Senathirajah S. , Lewis D. 
Published: September 2009

SUMMARYWild-type strains ofCoprinus lagopusare sensitive to para-fluoro-phenylalanine and ethionine. Resistant mutants to these two analogues are known but all these mutants are recessive in a heterozygous dikaryon except for F7 (pfpr-3) which is semi-dominant. Resistance to two other analogues, however – canavanine sulphate and azetidine-2-carboxylic acid – were found to be wild-type features. One strain ofC. lagopussensitive to canavanine was identified. Selection for canavanine resistance in monokaryons always yielded only dominant resistance, while selection for para-fluorophenylalanine resistance in monokaryons gave only recessive resistance. Canavanine-resistant mutants were due to a single gene mutation which, like the wild-type resistance, were dominant in heterozygous dikaryons. The wild-type resistance was also dominant in a diploid but the mutant resistance was recessive. Selection for resistance to para-fluorophenylalanine in auxotrophically balanced dikaryons resulted in the identification of two new loci (pfpr-10 andpfpr-ll), and two specific dominance modifiers (mod+-10 andmod+-ll). In the absence of the specific modifier,pfpr-10 andpfpr-ll were recessive while, in the presence of even one dose of the specific modifier, resistance was dominant in the dikaryon. Thepfpr-10 andpfpr-ll even in the presence of two doses of modifier were fully recessive in the diploid. The action of the modifier genes and the reversal of dominance in dikaryon and diploid is discussed in terms of negative complementation in an oligomeric product of thepfprgene and localized translation of the relevant mRNA in the cell with the modifier acting as a reinforcer of localization.
Reversion studies withexrBinEscherichia coli
Authors: Greenberg Joseph , Berends Leonard , Donch John , Johnson Ben 
Published: September 2009

SUMMARYexrBderivatives of H/r30 and WP2 are sensitive to ultraviolet radiation (UV), methylmethane sulphonate (MMS) and will not form colonies at 42 °C. Revertants to wild type were selected by plating on either nutrient plates containing MMS or nutrient plates incubated at 42 °C. Revertants selected for MMS resistance were temperature- and UV-resistant, and all revertants selected for temperature resistance were MMS and UV resistant. The frequency with which revertants appeared on MMS plates was about eight times as high as it was at 42 °C, and the variance in frequency of revertants among cultures started with small inocula was higher on selection at 42 °C than on MMS. The spontaneous frequency was estimated to be 10−6to 10−7, sufficiently low to suggest a single mutational event. Among wild-type revertants selected at 42 °C there was a stable and an unstable class.exrB+could be co-transduced withmalB+from stable revertants to anexrBstrain, but could not from unstable revertants. None of the revertants could support the growth of amber or ochre mutants of phage T4, nor were amber and ochre suppressedexrBstrains wild type with regards MMS and temperature resistance. The presence of a polarity suppressor in anexrBstrain did not modify resistance to UV or temperature. Neither UV or MMS was able to induce mutations in anexrBstrain.
Mutants affecting histidine utilization inAspergillus nidulans
Authors: Polkinghorne Meryl , Hynes M. J. 
Published: September 2009

SUMMARYWild-type strains ofAspergillus nidulansgrow poorly onL-histidine as a sole nitrogen source. The synthesis of the enzyme histidase (EC. 4.3.1.3) appears to be a limiting factor in the growth of the wild type, as strains carrying the mutantareA102 allele have elevated histidase levels and grow strongly on histidine as a sole nitrogen source.L-Histidine is an extremely weak sole carbon source for all strains.Ammonium repression has an important role in the regulation of histidase synthesis and the relief of ammonium repression is dependent on the availability of a good carbon source. The level of histidase synthesis does not respond to the addition of exogenous substrate.Mutants carrying lesions in thesarA orsarB loci (suppressor ofareA102) have been isolated. The growth properties of these mutants on histidine as a sole nitrogen source correlate with the levels of histidase synthesized. Mutation at thesarA andsarB loci also reduces the utilization of a number of other nitrogen sources. The data suggest that these two genes may code for regulatory products involved in nitrogen catabolism. No histidase structural gene mutants were identified and possible explanations of this are discussed.
Profiles of electrophoretic alleles in natural populations
Authors: Brown A. H. D. , Marshall D. R. , Albrecht L. 
Published: September 2009

SUMMARYThe charge state model of Ohta & Kimura (1973) for the number of electrophoretically detectable alleles in a finite population, is extended to include mutations of both one and two charge changes. The effective number of alleles (ne) is increased only slightly by this extension. Electrophoretic profiles of neutral variants are shown on average to be leptokurtic and have their odd central moments equal to zero. The expected frequency distribution of pairs of gametes which differ by 1,2,3,… charge units can be obtained as the sum of the appropriate terms from two geometric series.
The control of mutational instability by a new mutator gene ofDrosophila melanogaster
Authors: Woodruff R. C. 
Published: September 2009

SUMMARYThe isolation and genetic characterization of a new mutator gene,Mutator-forked3N(Mu-f3N), ofDrosophila melanogasterare described. This mutator gene is unique in that it seems to increase specifically the reversion frequency of the unstable mutantforked3N(f3N, 1–56.7), since the frequency of spontaneous sex-linked recessive lethals in males and females and the frequency of reverse mutations at eight additional X-linked alleles were unaffected byMu-f3N. The mutator is a dominant gene that has been mapped to the region betweenf3N(1–56.7) andBeadex-2 (Bx2, 1–59.4) in theXchromosome, and it seems to function only in the ‘ cis’ configuration. The mode of action ofMu-f3Nis compared with that of other mutator genes.
Constitutive heterochromatin and karyotype variation in Indian pygmy mouse, Mus dunni
Authors: Sharma T. , Garg G. S. 
Published: September 2009

SUMMARYThe Indian pygmy mouse, Mus dunni, exhibits great variation in the number of chromosome arms while its diploid number of chromosomes remains constant. The variation seems to be due to addition or deletion of C-band positive constitutive heterochromatin in the short arms of autosomes.
Unusual characteristics of the receptor for the N sex factor-specific filamentous phage IKe
Authors: Dennison Sheena , Baumberg S. 
Published: September 2009

SUMMARYPlasmid-mediated sensitivity to filamentous phage IKe is shown to be a property exclusive to plasmids of the N incompatibility group. As with other sex factor-specific phages, IKe sensitivity results from the provision of a plasmid-encoded receptor. However, direct evidence for IKe adsorption to a sex pilus-like structure is so far lacking.Mutations in an N plasmid were obtained which affected IKe infect-ability and N transfer frequency simultaneously, though to different extents. IKe receptors could be removed to a limited extent by high speed blending, but only under more extreme conditions (higher speed and in low ionic strength medium) than F pili. As with F-specific filamentous phages, IKe adsorption was partially blocked by Zn2+.We tentatively suggest that the results accord with the IKe receptor being a sex pilus rather different from F and I pili (possibly in being much shorter in liquid culture), but other interpretations of these data are possible.
Altered instability due to genetic changes in a duplication strain ofAspergillus nidulans
Authors: Azevedo J. L. 
Published: September 2009

SUMMARYStrains ofAspergillus nidulanswith a duplicate segment are mitotically unstable; they produce phenotypically improved variants following deletions in either duplicate segment, and morphologically deteriorated types. The number of variants produced is characteristic of each duplication strain under the same conditions. After ultraviolet treatment two variants, one more stable and the other less stable than the original strain, were selected. Genetic analysis showed that the increased instability in the less stable variant was due to a translocation involving linkage groups V and VIII. The increased stability of the more stable variant was due to a recessive factor (stf–1) located in linkage group VIII. In the homozygous condition this factor also reduces the number of sectors in a diploid strain. The possible genetic mechanisms explaining the instability alterations are discussed.
The inheritance of resistance to eyespot (Cercosporella herpotrichoides) in wheat
Authors: Law C. N. , Scott P. R. , Worland A. J. , Hollins T. W. 
Published: September 2009

SUMMARYThe genetic control of resistance to the fungus,Cercosporella herpotrichoides, causing the eyespot disease of wheat was studied using the Chinese Spring (Cappelle-Desprez) chromosome substitution lines andF2monosomic families of hybrids between Cappelle-Desprez and Mara. Chromosome 7A of Cappelle-Desprez was found to increase resistance to eyespot in both types of test. Chromosomes 2B and 5D of Cappelle-Desprez gave increased resistance compared to their homologues in Mara on anF2background. When substituted into Chinese Spring neither of these chromosomes appeared to increase resistance. Chromosome 1A of Cappelle-Desprez in a Chinese Spring background increased the level of infection. Dominance was towards resistance and the presence of between-chromosome interaction could be deduced.
Genetic assimilation of part of a mutant phenotype
Authors: Thompson James N. , Thoday J. M. 
Published: September 2009

SUMMARYWhen the mutantveinletwas removed from aDrosophila melanogasterline selected for shortened vein length it was found that the selected polygenic background produced vein gaps in the absence of the major mutant. This example of genetic assimilation was unusual, however, in that the phenotype of the assimilated line was not exactly the same as the phenotype of the original selection line. It differed in two respects: only one of the longitudinal veins was affected in the assimilation line whereas all veins are shortened in the selectedveline, and vein gaps were sub-terminal in the assimilated line whereas they are terminal inveinlet. Modifiers of L 4 vein length were found to be located on both chromosomes II and III, though the chromosome II factor had a larger effect and was required for gap formation. The chromosome II gene was mapped to the same position as a similar L 4 vein length polygene (PL(2)L4a) found in anotherveinletselection line and reported elsewhere. The pattern of expression of thevemutant and the assimilated line genotype were compared using profiles of vein frequency at given points. The vein pattern profiles are discussed in relation to an hypothesis to explain the observed selection response and the effectiveness which these polygene combinations showed in modifying the much more complexveinletphenotype.
Selection at the alcohol dehydrogenase locus in Drosophila melanogaster imposed by environmental ethanol
Authors: Oakeshott J. G. 
Published: September 2009

SUMMARYThis paper describes selective differences imposed by environmental ethanol on six genotypes at the alcohol dehydrogenase (Adh) locus in Drosophila melanogaster. Probit analyses were used to relate differences between the percentage survival of adults of different Adh genotypes to ethanol concentration. Regression analyses were used to relate differences between the pre-adult developmental times of different Adh genotypes to ethanol concentration. The directions of differences between some of the genotypes were found to differ in these two components of fitness. The differences in developmental time are linearly related to the differences in the in vitro alcohol dehydrogenase activity expressed by these genotypes. Percentage survival differences amongst adults are not linearly related to these differences in enzymic activity. The development of AdhF AdhF pre-adults is retarded the least on ethanol impregnated media but AdhFAdhS adults are most likely to survive on such media.
Three genes determine the carboxin sensitivity of mitochondrial succinate oxidation inAspergillus nidulans
Authors: Gunatilleke I. A. U. N. , Arst H. N. , Scazzocchio C. 
Published: September 2009

SUMMARYPartially dominant mutations to carboxin resistance occur in three, freely recombining, nuclear genes inAspergillus nidulans. Mutations at all three loci reduce carboxin inhibition of succinate dehydrogenase (EC 1.3.99.1), succinate-cytochromecreductase (EC 1.3.99.1) and succinate oxidase (EC 1.3.99.1) in mitochondrial preparations. It is therefore probable that the ability of carboxin to prevent growth ofA. nidulansis a direct consequence of its ability to prevent succinate oxidation.
Non-autonomy in achaete mosaics ofDrosophila
Authors: Claxton J. H. , Kongsuwan Kritaya 
Published: September 2009

SUMMARYNumbers of bristles are reduced in the dorsocentral regions of achaeteDrosophila melanogaster. In achaete tissue of mosaics the effect is not uniform, and near the clone boundaries bristle numbers are significantly higher than they are elsewhere in the clone. It is argued that the cause of this non-autonomy stems from ‘factors’ that spread into the achaete clone from surrounding non-achaete cells.
Genetic analysis of morphogenetic processes in Paramecium: I. A mutation affecting trichocyst formation and nuclear division
Authors: Ruiz Françoise , Adoutte André , Rossignol Michèle , Beisson Janine 
Published: September 2009

SUMMARYMutation tam38 of Paramecium tetraurelia is a nuclear recessive mutation with a pleiotropic effect on both trichocyst morphogenesis and nuclear processes. The analysis of the defective nuclear processes (micronuclear and macronuclear divisions, nuclear reorganization at autogamy) shows that these defects result from an abnormal localization of the nuclei. Phenocopies of tam38 abnormalities can be obtained by vinblastine treatment of wild-type cells at late stages of division. Taking into account the similarity between tam38 and a series of other mutations which also prevent trichocyst attachment to the cell surface and disturb nuclear divisions, the following interpretation is proposed: the absence of attached trichocyst induces structural changes in the plasma membrane or in the cortical region which disturb the normal cortical control of the localization of nuclei.
Gene expression and phenotypic change inParamecium tetraureliaexconjugants
Authors: Berger James D. 
Published: September 2009

SUMMARYA study of the patterns of phenotypic change in exconjugants using the recessive behavioural mutant pawn (pwA) and its wild-type allele shows that both cytoplasmic and nuclear factors contribute to phenomic lag. Following loss of the wild-type allele from the macronucleus, phenomic lag lasts for 6–11 cell cycles in various sublines of a single clone. Inherited cytoplasmic material is estimated to be responsible for phenomic lag of no more than 5–6 cell cycles. Longer persistence of the parental phenotype is due to continued gene activity in macronuclear fragments carrying the wild-type allele. Genes in fragments remain active and can result in maintenance of the parental phenotype as long as fragments are present (up to 11 cell cycles).Phenomic lag in the other direction, from pawn to wild type, varies from 0 to 2 cell cycles. The major cytoplasmic factor involved is the amount of wild-type material acquired from the mate during conjugation. Extensive cytoplasmic exchange often occurs during normal conjugation and can lead to change of phenotype as early as the first meiotic division. Phenotypic change due to gene expression in macronuclear anlagen brings about phenotypic change near the end of the first cell cycle in +/+ cells and about a cell cycle later in heterozygotes.
A modifier gene involved in the expression of the dominant mating type allele inParamecium caudatum
Authors: Hiwatashi Koichi , Myohara Koji 
Published: September 2009

SUMMARYMating type inParamecium caudatum, syngen 3 is determined by a pair of alleles with simple dominance; the recessive allele restricts homozygotes to mating type V and the dominant allele permits expression of mating type VI. Clones of mating type V never show natural selfing, but most clones of mating type VI self naturally. A mutant clone of mating type VI which never selfed over a period of more than 3 years was obtained by treatment withN-methyl-N′-nitro-N-nitrosoguanidine. When this mutant clone was crossed to a wild-type stock of mating type V, all F1clones of mating type VI gave rise to selfers. From selfing of these F1of mating type VI, clones of F2were obtained. Nearly 3:1 segregation of selfer to non-selfer clones was observed among the F2clones of mating type VI. The results were consistent with the interpretation that a dominant modifier gene,Su(+mtV), controls the instability in the expression of mating type VI.
Quantitative predictions of random segregation models of the ciliate macronucleus
Authors: Preer John R. 
Published: September 2009

SUMMARYModels of the macronucleus inParamecium tetraureliawhich assume known levels of ploidy and random segregation of subunits smaller than a haploid set at both fission and macronuclear regeneration (MR) are not consistent with the hypothesis that senescence is due to aneuploid imbalance. Either senescence has some other basis or there is a mechanism for regular distribution of subunits at MR. Random segregation models for fission and MR are consistent with most data on survival and heterozygote stability, but if the ploidy level is 860 they fail to account for the data of Nyberg (this volume). Since the ploidy level may be higher than 860, models of random segregation cannot be ruled out forParamecium. Models of the macronucleus in hypotrichs which assume randomly segregating chromosome fragments are consistent with data on survival and on stability of heterozygous genotypes at fission.