bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conditional mutations affecting the cell envelope ofEscherichia coliK-12
Authors: Egan A. F. , Russell R. R. B. 
Published: September 2009

SUMMARYAmongst a collection of temperature sensitive (TS) mutants ofEscherichia coliK-12, some have been found which can grow at the restrictive temperature (42 °C) if the osmotic pressure of the medium is raised by the addition of sodium chloride (1%) or sucrose (12·5%). These mutants are described as temperature sensitive osmotic remedial (TSOR) mutants. At the restrictive temperature they are not osmotically fragile, but do display decreased resistance to inhibitory agents such as deoxycholate, actino-mycin D and acridine orange; they also show release of the periplasmic enzyme ribonuclease. These results indicate a change in the cell's outer permeability barrier. The genes affected in six of the mutants have been located on theE. colilinkage map. The mutations, which occur at loci not previously described, have been namedenvM–envTto indicate their effect on the cellenvelope.
Random selective advantages of genes and their probabilities of fixation
Authors: Jensen Louis 
Published: September 2009

SUMMARYThe question of what is meant by random fluctuations in selection intensities in a finite population is re-examined. The model presented describes the change in the frequency of a gene in a haploid population of sizeM. It is assumed that in any generation the adaptive values ofAandaare equally likely to be 1 +s: 1 or 1: 1 +s. Ifsis the selective advantage andxthe frequency of geneA, then the first two moments of the change in frequency are found to bem(Δx) =x(1 −x)(1 − 2x) θ/2MandwhereE(s2) = θ/M. The ultimate probability of fixation is computed, showing that variability in selection increases the chance of fixation of a rare gene. A more general form form(Δx) also is obtained. This form is compared with the equation currently used in describing random fluctuations in selection intensities.
Genetic control of metabolism: enzyme studies of theobeseandadiposemutants in the mouse
Authors: Bulfield Grahame 
Published: September 2009

SUMMARYThe activity of several enzymes has been determined in the livers of homozygousobeseandadiposemice, their normal litter-mates, and phenocopies induced in normal mice by aurothioglucose (ATG) injections.Obese, adiposeand ATG mice had higher activities of ATP citrate lyase, malic enzyme (NADP malate dehydrogenase) and pyruvate kinase than normal mice. Heterozygote activities are indistinguishable from wild-type. There was no difference between normal and fat litter-mates in the activity of malate dehydrogenase (NAD-linked), lactate dehydrogenase, isocitrate dehydrogenase and fumarase.Crosses between mice doubly heterozygous for roth theadandobgenes produced offspring that were only ‘fat’ or ‘normal’ and no offspring could be phenotypically recognized as the double mutant, either physically or in terms of ATP citrate lyase activity.Gas–liquid chromatography of the fatty acids of the depot fat showed no differences between any of the types of litter-mate.The alterations found in enzyme activity inobeseandadiposemice are compared to several other enzyme activity differences reported in the literature forobesemice. These are discussed in relation to genetical criteria that may be estarlished to assess, from quantitative data, whether an enzyme is the site of the primary lesion in a mutant pheno-type. Some general observations are made on genetics and the control of metabolism.
Deoxyribonuclease-deficient mutants ofUstilago maydiswith altered recombination frequencies
Authors: Badman Rosemary 
Published: September 2009

SUMMARYCurrent molecular models of genetic recombination invoke steps mediated by deoxyribonucleases. It is likely therefore that some mutants deficient in these enzymes would have defective recombination mechnisms. Mutants ofUstilago maydisdeficient in extracellular and intracellular DNase activity have been isolated. Three of the extracellular mutants are recessive and non-complementing, as are four of the intracellular mutants. The loci for extracellular and intracellular DNase deficiency have been namednuc-1andnuc-2respectively, and they are linked.In crosses where each parent was deficient in both extracellular and intracellular DNase activity, meiotic allelic recombination (gene conversion) within thenarlocus was abolished, although crossing-over in one tested interval was apparently normal in frequency. In DNase-deficient diploids, no mitotic allelic recombination in thenarlocus was observed and the distribution of crossing over was abnormal. Nuclease deficiency did not appear to have any strong effect on radiation sensitivity.
Physiological genetics of melanotic tumours inDrosophila melanogasterVII. The relationship of dietary sterols to tumour penetrance
Authors: Cooke Jonathan , Sang J. H. 
Published: September 2009

SUMMARYA strain ofDrosophila, homozygous for the variably penetrant genetu bw, which causes the formation of abnormal masses of melanizing haemocytes (melanotic tumours), has been reared on defined axenic diets containing various sterols, both singly and in pairs. Both optimal and deficient nutritional levels of sterol have been employed, as well as certain sterols inadequate by themselves to support development. The effect of these diets upon probability of tumour formation has been studied in relation to their nutritional adequacy, as defined by the growth-rate, survival, and in one case, adult body-weight.The results demonstrate a rather complex pattern of interaction between dietary sterols in determining the variables of the phenotype produced, under circumstances suggesting that all the sterols investigated have entered the developing larvae. There is only a partial overall correlation, and occasionally an inverse relationship, between tumour suppressant and growth-promoting properties of particular sterols. Within single molecules, structural sterol features tend to exert their characteristic effects additively upon the phenotype, except for an inadequacy in utilization of molecules containing the Δ7double bond, which dominates at low concentrations. With pairs of dietary sterols, however, non-additive or ‘saving’ effects are sometimes seen.It is suggested that thetu bwallele allows the resolution of several discrete developmental functions for sterols and/or their immediate metabolic products inDrosophila, which cannot synthesize its own sterol. However, the molecular nature of these functions is little understood.
The estimation of the number of mutationally silent loci in saturation-mapping experiments
Authors: Barrett John A. 
Published: September 2009

SUMMARYWhen the technique of saturation mapping is employed to estimate the number of loci in a distinct chromosomal region, there is always the possibility that some loci will not be detected. If the number of mutants per locus follows a Poisson distribution, the number of mutationally silent loci can be estimated. This paper describes a method for fitting such data to a Poisson distribution truncated at the zero class and a method for estimating the number of mutationally silent loci. The use of these methods is demonstrated by their application to some published data.
Polymorphism in a varied environment: how robust are the models?
Authors: Smith J. Maynard , Hoekstra R. 
Published: September 2009

SUMMARYThis paper shows that a number of models of the maintenance of polymorphism in a heterogeneous environment, including those of Levene and Dempster, can be derived from a simple assumption about the way in which the numbers and kinds of individuals emerging from a niche depend on the number of eggs laid in it. It is shown that for such models, unless selective advantages per locus are large, protected polymorphism requires that the relative niche sizes lie in a narrow range. This lack of robustness applies also to models of stable polymorphism proposed by Clarke and by Stewart & Levin. Excluding models relaying on habitat selection or restricted migration, the only models which may escape this criticism are diploid models with partial dominance with respect to fitness, such as one proposed by Gillespie, in which in all niches the fitness of heterozygotes is higher than the arithmetic mean of the homozygotes.
Testing for rare male mating advantages among various Drosophila melanogaster genotypes
Authors: Markow T. A. , Richmond R. C. , Mueller L. , Sheer I. , Roman S. , Laetz C. , Lorenz L. 
Published: September 2009

SUMMARYExperiments were conducted to look for minority male mating advantages among several Drosophila melanogaster genotypes. The strains of flies used were Canton-S, Oregon-R, a strain carrying the recessive mutation vermilion, and highly geo-positive and geo-negative populations which had been selected for over 200 generations in Hirsch-geotaxis mazes. Two series of experiments were carried out, one series using ten pairs of flies, and another series using 20 pairs. Regression analysis gave one significant slope out of seven, suggesting that in the present study, frequency-dependent advantages are not as common or as strong as reported for D. pseudoobscura.
The interpretation of gene conversion data from ordered eight-spored asci
Authors: Fincham J. R. S. , Hill W. G. , Reeve E. C. R. 
Published: September 2009

SUMMARYCurrently favoured models postulate that gene conversion is due to the correction of mis-matches in heteroduplex DNA. If heteroduplex is formed reciprocally on both chromatids participating in recombination, the mis-matches due to a heterozygous site will be different on the two chromatids, and there will be four correction probabilities to be taken into account. It is shown that, given the frequencies of the five different kinds of aberrant ascus ratios, it is possible to calculate four alternative sets of values for the four correction probabilities and the total number of asci in which heteroduplex is formed. These four solutions reduce in effect to two when there are no other markers distinguishing the two chromatids. With the aid of flanking markers and the assumption that heteroduplex formation is chemically polarized, it is possible, in principle, to choose one best solution.The method has been applied to the five one-point crosses inSordaria fimicolafrom which most data are available. The data from four different mutants crossed to wild type are compatible with a restricted model in which the correction frequencies, from mutant to wild and from wild to mutant, are the same on both chromatids. In the case of the fifth mutant the data are not consistent with this restricted model, and indicate different correction frequencies in the two chromatids.
Pigmentation and lysosome function in mice homozygous for both pale ear and Beige-J pigment genes
Authors: Novak Edward K. , Swank Richard T. , Meisler Miriam H. 
Published: September 2009

SUMMARYWe have examined mice doubly homozygous for both pale ear (ep/ep) and beige (bgJ/bgJ) mutations in order to detect genetic interactions between these 2 loci affecting pigmentation and lysosome physiology. The doubly homozygous mouse has a new pigmentation phenotype consistent with independent effects ofepandbg. The beige (Brandt, Elliott & Swank, 1975) and pale ear (Novak & Swank, 1979)genes have abnormal kidney lysosomal enzyme accumulation caused by defective secretion into urine. No cumulative effect on these functions was observed in the new double mutant phenotype. The new phenotype has giant lysosomes typical of the beige mutation. Unexpectedly, the beige gene corrects the effect of the pale ear on serum lysosomal enzyme concentration. There is also a gene dosage effect of the beige gene on this serum lysosomal enzyme phenotype. The results suggest that the beige and pale ear genes affect the same pathway(s) of lysosome biosynthesis and/or processing. The action of the beige gene may precede that of the pale ear gene in lysosome physiology.
Random genetic drift in an egg-laying strain of poultry
Authors: Foster W. H. , Thompson R. 
Published: September 2009

SUMMARYA pedigreed control strain was divided into three lines which were maintained genetically distinct over nine generations. Mean coefficients of inbreeding of about 0·1 were attained. Results suggest that discernible genetic drift had occurred in several traits. Separate estimates of genetic variance were obtained from observed variation between and within lines. These estimates differed significantly in the case of only one of the eight traits observed. Observed variation between lines agreed reasonably well with that predicted.
The kinetics of transfer of nonconjugative plasmids by mobilizing conjugative factors
Authors: Levin Bruce R. , Rice Virginia A. 
Published: September 2009

SUMMARYA mathematical model for the kinetics of transfer of non-selftransmissible (nonconjugative) plasmids by mobilizing conjugative factors is presented and methods to estimate its parameters described. Using batch and chemostat cultures ofEscherichia coliK-12 with the nonconjugative plasmid pCR1 and an F′ mobilizing factor, the parameters of this model were estimated. The observed changes in concentrations of the different parental and transconjugant cell types and the changes in these concentrations anticipated from the model are presented for two different ‘mating’ combinations in both exponentially growing and equilibrium chemostat populations ofE. coli. The results of these experiments are interpreted to suggest that for bacterial populations dividing at a constant rate in liquid culture, the kinetics of mobilization transfer of nonconjugative plasmids can be reasonably well described by a simple set of mass action differential equations. These results also suggest that the carriage of the nonconjugative plasmid pCR1 has little, if any, effect on the capacity of a host bacterium to donate or receive conjugativeF′plasmids.
A mutant sex factor ofPseudomonas aeruginosa
Authors: Stanisich V. A. , Holloway B. W. 
Published: September 2009

SUMMARYA mutant with the properties of a recipient has been isolated from theP. aeruginosadonor strain PAT (FP 2 + ) following treatment with the acridine-mustard ICR-191. While this strain displays the properties expected of a female or recipient in a number of genetic tests, the FP 2 determined property of mercury resistance is retained by the strain, suggesting that it may carry the FP2 factor in a mutated form. Treatment of the donor strain PAT (FP2 + ) with acridine-mustard has produced mutant male strains with the ability to form recombinants with other male strains at frequencies similar to that obtained in FP2+ × FP2 − matings. This characteristic has been shown to be due to a mutation in the FP2 factor which is dominant to the wild-type function. The isolation of stable male strains carrying both the mutant and wild type forms of the sex factor suggests that more than one copy of the FP 2 factor occurs inP. aeruginosastrain PAT donors.
The effect of an inverted chromosome segment on intragenic recombination in another chromosome ofSordaria brevicollis
Authors: Ahmad A. F. , Bond D. J. , Whitehouse H. L. K. 
Published: September 2009

SUMMARYAn inverted segment in one of the chromosomes ofSordaria brevicollishas been found to have a marked effect on recombination within a gene in another chromosome. There are two effects on the intragenic recombination pattern, namely, a change in the polarity of recombination and a change in the frequency of parental and recombinant outside markers. The results support the idea that a mechanism exists for cancelling crossovers shortly after they have been formed as a means of controlling their number.
Genetic studies on flagellum mutants ofChlamydomonas reinhardii
Authors: McVittie Anne 
Published: September 2009

SUMMARYEight newly isolated 9 + 0 mutants each mapped at one of the four previously known loci. Short flagellum mutants were at three loci, two of which (pf7andpf8) were closely linked; the third,pf21, was unlinked to these two and mapped on linkage group II. The long flagellum mutantslf1andlf2were on linkage groups II and XII respectively. Mutantspf8Aandlf1were both recessive to wild-type. There was no evidence for non-Mendelian flagellum mutants.
The integration of autonomous transmissible plasmids into the chromosome ofEscherichia coliK12
Authors: Moody Eric E. M. , Runge Richard 
Published: September 2009

SUMMARYThe highly selective technique of integrative suppression has been used to determine the ability of autonomous transmissible plasmids to integrate into theE. colichromosome.All theF-like transmissible plasmids appear to be able to integrate, suppress the initiation defect and formHfr-type donor strains. However, there is no evidence of integration with theI-like transmissible plasmids examined.
Genetic fine structure, site clustering and marker effect in theftrcistron ofCoprinus
Authors: Moore David 
Published: September 2009

SUMMARYMutants in theftrcistron of the BasidiomyceteCoprinus lagopushave a lesion in sugar transport. Fifty-two alleles are placed in an allele map using recombination frequencies obtained from over 400 heteroallelic crosses. The mutant sites in the allele map are distinctly clustered into three approximately equally spaced regions. It is demonstrated that the clustering is not due to any mutational specificity. Evidence is presented which indicates that the clusters are functionally differentiated both within themselves and from one another. Additivity of recombination frequencies was good over the whole of the allele map and there was no overall map expansion. However, specific marker effect sites could be recognized. The data indicate that marker effect may act to enhance or reduce recombination frequency and that enhancement is equal and opposite to reduction. It is also shown that marker effect enhancement is only observed when the interval being mapped exceeds a certain minimum value, but that there was no upper limit to the size of the interval. Expression of marker effect was influenced both by the background genome and by the nature of the mutation at the second site in the heteroallelic cross. It is suggested that current models of recombination do not adequately explain these data and, more importantly, that then-reliance on initial breakage of DNA strands in the formation of hybrid DNA creates grave mechanical difficulties. A model for genetic recombination is proposed in which the sequence of events is: (i) separation of intact double helices into single strands; (ii) illegitimate pairing between single strands from non-sister chromatids; (iii) strand breakage and exchange of covalent links so as to legitimize the illegitimately paired regions. The model allows for the formation of hybrid DNA either with or without coincident chiasmata. It is envisaged that the error recognized by any excision-repair system involved in recombination is the tangled strands at each end of the illegitimately paired region rather than base mismatching; and that the exchange of covalent links in stage (iii) involves the excision and replacement of segments of DNA.
The hitch-hiking effect of a favourable gene
Authors: Smith John Maynard , Haigh John 
Published: September 2009

SummaryWhen a selectively favourable gene substitution occurs in a population, changes in gene frequencies will occur at closely linked loci. In the case of a neutral polymorphism, average heterozygosity will be reduced to an extent which varies with distance from the substituted locus. The aggregate effect of substitution on neutral polymorphism is estimated; in populations of total size 106 or more (and perhaps of 104 or more), this effect will be more important than that of random fixation. This may explain why the extent of polymorphism in natural populations does not vary as much as one would expect from a consideration of the equilibrium between mutation and random fixation in populations of different sizes. For a selectively maintained polymorphism at a linked locus, this process will only be important in the long run if it leads to complete fixation. If the selective coefficients at the linked locus are small compared to those at the substituted locus, it is shown that the probability of complete fixation at the linked locus is approximately exp (− Nc), where c is the recombinant fraction and N the population size. It follows that in a large population a selective substitution can occur in a cistron without eliminating a selectively maintained polymorphism in the same cistron.
The inheritance of drug resistance and compatibility type in Phytophthora drechsleri
Authors: Khaki Ikram A. , Shaw D. S. 
Published: September 2009

SummaryMethods have been developed for the selection of mutants resistant to p-fluorophenylalanine, chloramphenicol and actidione. Resistance to p-fluorophenylalanine and to chloramphenicol was inherited as if determined in each case by a single dominant allele present in diploid somatic nuclei. Inheritance of mating type was anomalous in crosses involving drug-resistant mutants. Presumptive mating-type heterokaryons were generated in a few per cent of sexual progeny from a wild-type cross.
A stable duplication of the rII region of bacteriophage T4
Authors: van de Vate C. , van den Ende P. , Symonds N. 
Published: September 2009

SummaryIn the preceding paper (Van de Vate & Symonds, 1974) a deletion, sdl, has been reported that stabilizes an rII diploid by penetrating into the region of the duplication from the right-hand side (if we take the rIIB gene located to the right of rIIA). Here we wish to report on a different stabilizing deletion, sd2. Evidence will be presented in favour of penetration of the duplication from the left-hand side. The right-hand terminus of the deletion is located within the rIIA gene.
Location of prophage H90 on the chromosome ofPseudomonas aeruginosastrain PAO
Authors: Carey K. E. , Krishnapillai V. 
Published: September 2009

SUMMARYProphage H90 has been found to undergo a phenomenon similar to zygotic induction, during conjugal transfer from a lysogenic donor to a non-lysogenic recipient.It has not been possible to demonstrate that the level of infectious centres increases concomitantly with transfer of the prophage. However, the genetic consequence of zygotic induction was observed with regard to decreased recombinant yield of markers distal to the prophage. This latter fact has been exploited in interrupted mating experiments, to locate the prophage at between 5 and 7 min on thePseudomonas aeruginosastrain PAO map. It was further shown by transduction experiments that the prophage does not appear to be linked to clusters of co-transductional markers at the 5 and 7 min locations.
A new method of detecting centromere linkage in homothallic yeast
Authors: James A. P. 
Published: September 2009

SUMMARYA method is described for detecting centromere linkage inSaccharomyces cerevisiaeusing a simple monohybrid for the locus in question. The method utilizes the two-spored asci produced by a normal homothallic diploid and depends upon a selective elimination of specific chromatids during spore formation. The pattern of selective elimination was not detected in a heterothallic strain but was found to be a dominant trait in an inter-strain cross. It was shown that gross chromosome aberrations are probably not responsible for the two-spored asci produced by either the heterothallic or homothallic strains.
Transmissible plasmid coding for the degradation of benzoate andm-toluate inPseudomonas arvillamt-2
Authors: Wong C. L. , Dunn N. W. 
Published: September 2009

SUMMARYPseudomonas arvillamt-2 (ATCC 23073) has been shown to harbour a transmissible plasmid which codes for the degradation of benzoate andm-toluate. Plasmid-borne genetic information codes for the conversion of these compounds to catechol then the assimilation of catechol via themetacleavage pathway.