bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of the resistance mediated by several R-factors to Tetracycline and Minocycline
Authors: Robertson J. M. , Reeve E. C. R. 
Published: September 2009

SUMMARYThe resistance levels conferred by the T-determinants in four R-factors to Tetracycline and Minocycline in cells ofEscherichia coliK 12, before and after induction of maximum resistance by treatment with sub-inhibitory concentrations of the drugs, are measured by simple growth-and-challenge tests. The effect of a plasmid TKwhich confers tetracycline resistance on its hostKlebsiella aerogenesis tested in the same way. The five T-determinants fall into a high-level and a low-level group for resistance, the former giving 3- to 4-fold higher resistance in both induced and uninduced cells than the latter. The T-determinants all confer much lower resistance to Minocycline (a tetracycline molecule modified at the C-6 and C-7 positions) than to Tetracycline. The main cause of this difference is that cells carrying a T-determinant exclude Minocycline much less efficiently than Tetracycline, but in addition Minocycline is less effective than Tetracycline in inducing increased resistance. These results are discussed in the light of a model put forward to explain the inducible nature of R-factor resistance to the tetracyclines.
A subvital gene inRana pipienslinked to the Burnsi locus
Authors: Browder Leon W. 
Published: September 2009

SUMMARYA cross of a leopard frog heterozygous for the dominant Burnsi gene (B/ +) with a wild-type (+ / +) resulted in a large excess ofB/ + progeny. Two descendent lines established by theseB/ + progeny are characterized by excess +/ + progeny. These seemingly contradictory data are reconciled by postulating the existence of a dominant subvital gene (Sbv) linked to the + allele of Burnsi in the initial cross. Progeny used to establish subsequent lines were recombinants withSbvlinked toB. This proposed linkage would constitute the first case of linkage between two mutant loci in anuran amphibians.
Non-random association between electromorphs and inversion chromosomes in finite populations
Authors: Nei Masatoshi , Li Wen-Hsiung 
Published: September 2009

SUMMARYWith the aim of knowing the probable magnitude of non-random association between inversion chromosomes and electromorphs, both deterministic and stochastic studies are conducted on the evolutionary change of non-random association, which is defined as the difference in the frequency of a given allele between inversion and non-inversion chromosomes. In these studies inversion chromosomes are assumed to be subject to selection but electromorphs are selectively neutral, and recombination is allowed to occur between inversion and non-inversion chromosomes with a low frequency. The deterministic study has shown that in a variety of selective schemes for inversion chromosomes the non-random association decays at a rate equal to the recombination value in every generation. Thus, if the recombination value is of the order of 10−5˜ 10−4, it would take a long time for the non-random association to disappear. Furthermore, the stochastic study has indicated that random genetic drift generates non-random association of inversions and electromorphs in finite populations and the standard error of non-random association often becomes larger than the mean. In addition to these problems the time required for the electromorph frequencies in the inversion and noninversion chromosomes to become equal in a finite population and the probability that the population of inversion chromosomes remains monomorphic for the allele which existed in the initial inversion introduced are studied. Considering all these quantities, it is concluded that data on the non-random association between electromorphs and inversions are not very informative for the study of the maintenance of protein polymorphism. It is also indicated that in the study of association between electromorphs and inversion chromosomes non-random association or Yule's coefficient of association has a better property than the usual linkage disequilibrium measure or correlation coefficient. Implications of this study on some experimental observations are discussed.
Mitotic recombination inMusca domesticaL. and its influence on mosaicism, gynandromorphism and recombination in males
Authors: Rubini P. G. , Vecchi M. , Franco M. G. 
Published: September 2009

SUMMARYIn the housefly, mosaics appear spontaneously but rarely. Sexual mosaics or gynandromorphs also appear in strains in which sex determination is based on autosomal sex factors. Rare cases of recombination in the male have been reported by some authors. In field and laboratory populations, mitotic plates with figures indicating exchange of chromatid segments are regularly observed in tissues of individuals of both sexes and at all stages of development. All these anomalies are interpreted as outward manifestation of the same phenomenon: mitotic recombination. The cytological basis of mitotic recombination, its relative frequency, its influence on linkage and genetic variability are discussed.
Transduction of inositol-fermenting ability demonstrating phylogenetic relationships among strains ofSalmonella typhimurium
Authors: Old D. C. , Dawes P. F. H. , Barker Ruth M. 
Published: September 2009

SUMMARYThe production of Inl+recombinants was readily demonstrated in transductional crosses from Inl+donor strains to Inl−recipient strains from different biotypes and biogroups. None of numerous crosses between different pairs of strains from biotypes 25 and 26 and the biogroup FIRN (biotypes 29, 30, 31 and 32) gave Inl+recombinants suggesting that theinlmutation was present at the same intragenic site in all of these strains. Strains of the FIRN biogroup (Fim−Inl−Rha−Bxyl−) are thought to have descended by successiverhaandfimmutations from an ancestral bacterium of biotype 25 (Fim+Inl−Rha+Bxyl−). The sites of theinlmutations in other Inl−biotypes (9, 10, 27 and 25hi) were independent and each was different from that in strains from biotypes 25, 26 and FIRN.
Construction of isomitochondrial and isonuclear strains for recombinational analysis of mitochondrial loci in S. cerevisiae
Authors: Kruszewska A. , Szcześniak B. 
Published: September 2009

SUMMARYIn the mitochondrial and nuclear genetic background of the 777-3A strain (op1, ade1, α) a set of strains with different nutritional requirements and mating types, carrying the op1 mutation versus its wild-type OP1 allele was constructed. This makes possible the use of strains with the same genetic background in recombinational analysis of mitochondrial loci.
Effects ofY-chromosome variants on the male behaviour of the mouseMus musculus
Authors: Stewart A. D. , Manning Aubrey , Batty Jennifer 
Published: September 2009

SUMMARYA study of crosses between CBA/FaCam and C57B1/6Fa mice revealed an effect of the origin of theY-chromosome on testis weight and aggressive behaviour, but failed to reveal any effect on sexual behaviour and androgen metabolism. There is therefore no evidence that androgens mediate theY-linked variation in aggressive behaviour and testis weight. On behavioural grounds, it is difficult to compare measures of sexual and aggressive behaviour, but it appears from these results that there are major genetic components on theY-chromosome controlling the development of sexual and aggressive behaviour which are distinct.
The genetic variability of polygenic characters under optimizing selection, mutation and drift
Authors: Bulmer M. G. 
Published: September 2009

SUMMARYThe effect of optimizing selection, mutation and drift on a metric character determined by a large number of loci with equal effects without dominance was investigated theoretically. Conditions for a stable equilibrium under selection and mutation, in the absence of drift, have been obtained, and hence the amount of genetic variability which can be maintained by mutation has been determined. An approximate expression for the average amount of genetic variability to be expected in the presence of drift in a population of finite size has also been obtained and evaluated.
Mutants inSaccharomyces lactiscontrolling both β-glucosidase and β-galactosidase activities
Authors: Tingle M. , Halvorson H. O. 
Published: September 2009

SUMMARYInSaccharomyces lactis, a class of mutants isolated for low β-glucosidase activity are reduced in activity for β-galactosidase as well. Genetic studies indicate that their properties are the result of a single mutation in a nuclear gene. In diploide containing a wild-type and mutant β-galactosidase allele, the mutant phenotype is partially dominant. The two enzymes can be separated physically and under appropriate conditions are induced independently in wild-type strains.
Fixation probability of a mutant influenced by random fluctuation of selection intensity
Authors: Ohta Tomoko 
Published: September 2009

SUMMARYThe probability of fixation of a mutant gene in a finite population was investigated by taking into account the effect of random fluctuation of selection intensity. It was shown that not only the product of the effective population number and average selection coefficient (Nes) is important, but also the ratio of the mean and the variance of selection coefficient (s/Vs) has an important influence on fixation probability. In particular, when this ratio is small, a mutant gene, even if selected against, becomes fixed in the population like a selectively neutral mutant. In general, when random fluctuation of selection intensity is not negligible it may be convenient to use ‘effective selection coefficient’. The bearing of the present findings on the neutral mutation-random drift theory of evolution and variation at the molecular level was discussed.
Is subline differentiation a continuing process in inbred strains of mice?
Authors: Hoi-Sen Yong 
Published: September 2009

SUMMARYTwo new sublines of the C57BL/Gr strain of mice have been studied which were derived from earlier sublines in which no genetic variance could be demonstrated. The incidence of some 31 minor skeletal variants was examined which could thus go up or down. As new subline differences have arisen with about the same frequency and mean magnitude of effect as in the past, there is no doubt that, at least in the C57BL strain, subline differentiation is a continuing process. Its high frequency (about 0·01 changes per character at risk per generation) is difficult to reconcile with spontaneous mutation rates of single genes in the mouse. The possibility must thus be considered that some other self-perpetuating processes or entities of some degree of stability are handed down in the lines of descent in which they have arisen, or perhaps become unmasked. There is no reason to suppose that this type of event is confined to inbred strains (in which it can be demonstrated fairly easily); it presumably occurs similarly in mixed stocks in which it would scarcely be detectable.
The average number and the variance of generations at particular gene frequency in the course of fixation of a mutant gene in a finite population
Authors: Maruyama Takeo 
Published: September 2009

SUMMARYIn the case of an allele which is going to become fixed in a population, the average number of generations for which the population assumes particular gene frequencies is investigated, using the diffusion approximation. Explicit formulas were obtained and they were checked by computer simulations. As a particular case, it is shown that if a new mutant that is selectively neutral is eventually fixed in a population of sizeN, it spends two generations on average at each of the intermediate frequencies (1/2N, 2/2N, …, (2N−1)/2N), and the variance at each frequency is four generations.
Natural selection for enzyme variants among parthenogenetic Daphnia magna
Authors: Hebert P. D. N. , Ward R. D. , Gibson J. B. 
Published: September 2009

SUMMARYThe frequencies of genetically determined electrophoretic variants of two enzyme systems in the parthenogenetic crustacean D. magna have been followed in two isolated populations. In both populations a marked excess of hetero-zygotes was found in the later samples. It is concluded that the observed changes in gene and genotypic frequencies are due to natural selection as both migration and genetic drift can be excluded.
Sexuality in Neurospora crassa II. Genes affecting the sexual development cycle
Authors: Vigfusson N. V. , Weijer J. 
Published: September 2009

SUMMARYEighteen male sterile mutants of N. crassa which block various stages of the sexual development cycle have been functionally categorized on the basis of complementation tests. Nine of these (those which block early stages of the sexual cycle) have also been analysed through recombination studies. On the basis of these data, a minimum of four genes appear to be involved in early stages of sexual development (i.e. probably prior to karyogamy) and several genes are indicated which control later stages of the cycle. Complementation phases with respect to sexual development in heterothallic Ascomycetes are discussed as well as a comparison of results obtained with expectations and with those obtained in related Ascomycetes.
A comparative study of the coats of chimaeric mice and those of heterozygotes for X-linked genes
Authors: Cattanach B. M. , Wolfe H. G. , Lyon M. F. 
Published: September 2009

SUMMARYThe coats of Ta–Ta+ and c–c+ chimaeric mice have been compared with those of Ta heterozygotes and animals heterozygous for an X-autosome translocation which causes c-variegation. With one exception all those features typical of the heterozygotes were found in their chimaeric counterparts, thus showing that the creation of two cell populations by X-inactivation can ultimately lead to the observed heterozygous phenotypes. The one exceptional feature not found in c-variegated chimaeric mice was the progessive increase in the proportion of pigmented hairs in c areas with age which occurs in X-autosome translocation heterozygotes.The coat of a Modp / + – Ta chimaeric animal was also investigated. Ta hairs showing only the colour effect of Modp were numerous, suggesting that Modp and Ta affect different cell populations. However, Ta hairs showing the structural effect of Modp were very rare. The two observations suggest Modp can operate independently upon two different cell types – melanocytes and hair follicle cells.
Multiple changes in lens protein composition associated with the CatFr gene in the mouse
Authors: Day T. H. , Clayton R. M. 
Published: September 2009

SUMMARYThe ocular cataracts produced by the dominant CatFr gene in the mouse, Mus musculus, are associated with quantitative changes in the lens proteins (crystallins). The three classes of crystallin are affected differentially in homozygotes. Heterozygotes show a smaller effect. The quantitative levels of crystallin subunits are also affected and these changes are different for each subunit. The overall loss in protein is not readily explicable hi terms of a generalised leakage or a general tendency to insolubilisation. Possible mechanisms for the action of the gene are suggested.
Chromosome mapping inPseudomonas aeruginosa
Authors: Pemberton J. M. , Holloway B. W. 
Published: September 2009

SUMMARYA more extensive linkage map ofPseudomonas aeruginosastrain PAO has been compiled from data obtained by both, conjugation and transduction procedures. All the markers examined are located on one linkage group and the available evidence suggests that the sex factor FP2 promotes transfer of the chromosome in a polarized manner from only one site on this linkage group.
Studies of aromatic biosynthetic and catabolic enzymes inUstilago maydisand in mutants ofU. violacea
Authors: Berlyn Mary B. , Giles Norman H. 
Published: September 2009

SUMMARYA multienzyme complex for five of the enzymes in the prechorismate portion of the aromatic biosynthetic pathway has been demonstrated inUstilago violacea, and has previously been reported inU. maydis(Ahmed & Giles, 1969). This complex is similar to that found inNeurospora crassaand other fungi. InU. violaceapolyaromatic-requiring mutants show pleiotropic deficiencies for all five of these enzymes, similar to the extreme pleiotropic polar mutants of thearomgene cluster in Neurospora (Giles, Case, Partridge & Ahmed, 1967a; Case & Giles, 1971). This result is interpreted as mutational evidence for anaromgene cluster inU. violaceacomparable to that inN. crassa. A second low molecular weight, heat-stable isozyme of dehydroquinase is shown to be present at high (constitutive) levels inU. maydis, as previously indicated by Ahmed & Giles (1969), but this activity is increased to extraordinarily high levels in cells grown in the presence of quinate. In contrast,U. violaceastrains do not grow on quinate, have a single, heat-labile dehydroquinase species, and lack activities for other enzymes in the quinate catabolic pathway.
Non-reciprocal intragenic mitotic recombination inDrosophila melanogaster
Authors: Kelly Patricia Tamarah 
Published: September 2009

SummaryX-ray-induced mitotic recombination within the lozenge locus ofDrosophila melanogasterwas found to be non-reciprocal. Recombination was detected by the presence of faceted spots in a smooth (lozenge) eye. Markers were present so that if recombination were reciprocal, equal numbers of vermilion and apricot-vermilion-coloured faceted spots would be formed. Of 19 faceted spots found among more than 60000 eyes examined, 10 were vermilion, 7 variegated (some vermilion and some apricot-vermilion-coloured facets), and 2 probably variegated. None was uniformly apricot-vermilion in colour. Four mechanisms for the formation of faceted spots are discussed: double reciprocal recombination, misrepair or gene conversion before chromatid replication, misrepair or gene conversion after chromatid replication, and misrepair or gene conversion followed by chromosome loss. The evidence most strongly supports the hypothesis that all faceted spots were formed by either misrepair following X-irradiation or gene conversion and were originally vermilion in colour. Subsequent chromosome loss from these vermilion cells led to the production of variegated spots. Variegated spots were generally smaller than those uniformly vermilion in colour, indicating that chromosome loss may occur with greater frequency in older irradiated larvae.
Suppressors of ‘blue’ mutations in yeast
Authors: Mitchell I. de G. , Bevan E. A. 
Published: September 2009

SummaryMutants ofSaccharomyces cerevisiaewhose colonies were blue when grown on nutrient agar medium containing methylene blue reverted to wild-type with white-colony phenotype at high frequency. This reversion was controlled by nuclear gene suppressors in some mutants, and by cytoplasmic suppressors in others. Each of the latter suppressed several independetly segregating blue mutants. These suppressors could be divided into two classes: suppression by petite mutations which behaved as recessives, and suppression by a cytoplasmic factor in respiration-sufficient cells which behaved as dominant over wild-type but might also be a mutation ofrho. A relationship between blue mutation and temperature sensitivity was suggested.
A stable duplication as an intermediate in the selection of deletion mutants of phage T4
Authors: van de Vate C. , Symonds N. 
Published: September 2009

SummaryA selective procedure is described for the isolation of deletions in phage T4. This is based on the properties of partial diploids which possess a tandem duplication covering the rII region. The starting-point of the procedure is a particular s1231/3157 diploid which has a high segregation frequency and so possesses a long duplication. The replacement in this diploid of the large deletion 3157 by the small one 196 further increases the length of this duplication and removes the terminal redundancy of the resulting phage which are then non-viable. New compensating deletions which restore the terminal redundancy and thus the viability to these diploids are thereby selected. Nine new independent T4 deletions have been isolated by this procedure. The length of three has been estimated by terminal redundancy measurements and each found to be appreciably longer than the rII region. While developing the isolation procedure a key diploid intermediate was identified with the property that is was completely stable; that is, unlike typical diploids which continually generate haploid segregants during phage multiplications, this diploid strain produced no viable haploid segregants. This unexpected finding led us to examine the general problem of how tandem duplications can be stabilized. The solution we propose here is a structural one involving new stabilizing deletions which penetrate into one arm of the duplication removing certain essential genes. These stabilizing deletions are located in such a way that all haploid segregants formed by recombination are necessarily non-viable. Further investigations of the original stable diploid, and others isolated subsequently, validated this model for these phage diploids. It also led to the recognition of several novel genetic structures involving repeated DNA sequences which, together with the concept of the stabilizing deletions, could be of general significance.
A simple and rapid technique for obtaining a high proportion of hybrid cleistothecia in Aspergillus nidulans
Authors: Bainbridge B. W. 
Published: September 2009

SummaryA technique is reported for crossing strains of Aspergillus nidulans which produces hybrid cleistothecia in 7 days. The method depends on the partial inhibition of cleistothecium formation of auxotrophic mutants by growth-factor limitation. Cleistothecia form at the junction of two strains inoculated on to complete medium. The method has a number of advantages over standard techniques.
The regulation of NADL-glutamate dehydrogenase inAspergillus nidulans
Authors: Kinghorn J. R. , Pateman J. A. 
Published: September 2009

SummaryWild-type cells ofAspergillus nidulanshave undetectable NADL-glutamate dehydrogenase activity when utilizing glucose and high levels of NADL-glutamate dehydrogenase when utilizing certain amino acids as sole carbon sources.A mutant, designatedgdhCl, has appreciable NAD-GDH activity when utilizing glucose as a carbon source. ThegdhC1mutation is semi-dominant and is located in linkage group III.
The order of replication of chromosomal markers inPseudomonas aeruginosastrain 1: I. Marker frequency analysis by transduction
Authors: Booker R. J. , Loutit J. S. 
Published: September 2009

SUMMARYThe generalized transducing phage F116 has been used to prepare lysates from fast- and slow-growing cultures ofPseudomonas aeruginosastrain 1. These lysates have been used to transduce a number of auxotrophic markers to prototrophy and the ratios of the numbers of transductants obtained with each lysate have been determined. Since the markers are those which have been mapped by conjugation in previous studies it has been possible to compare the ratios obtained for each marker with the relative position of the marker on the chromosome map. If the assumption is made that there is only one circular chromosome inP. aeruginosastrain 1 it is possible to suggest a way in which two apparently unlinked segments might be joined together. It is also possible to suggest that the chromosome replicates sequentially in two directions from a fixed origin.