bluuebunny/crossref_metadata_2025_split huggingface dataset:
Genetic studies of class 2 nonsense suppressors inEscherichia coli
Authors: Rothwell M. Anne , Green Michael H. L. , Bridges Bryn A. 
Published: September 2009

SUMMARYThree genetically distinct ochre suppressors have been identified in a strain ofEscherichia coliB/r, all of which suppress a tyrosine auxotrophy and classify as class 2 by phage suppression pattern. One ochre suppressor, which was obtained by conversion from a class 2 amber suppressor, and a second ochre suppressor obtained directly from the non-suppressing parent, were found to have separate map locations, though a peculiar phenotype with regard to a leucine auxotrophy is exhibited by strains carrying either suppressor. We suggest that both suppressors correspond to separate genes for glutamine-insertingtRNA. A Leu+mutant of a strain carrying one of these suppressors was studied and was found to contain a further nonsense suppressor having amber-suppressing activity at a reduced level. We suggest that this suppressor might result from a mutation in another part of the translational machinery concerned with glutamine insertion. The third ochre suppressor has no effect on the leucine auxotrophy and mapping data suggest that it may besupL, an ochre suppressor probably inserting a different amino acid, from glutamine.
Aeruginocin tolerant mutants ofPseudomonas aeruginosa
Authors: Holloway B. W. , Rossiter Heidi , Burgess Diana , Dodge Judy 
Published: September 2009

SUMMARYMutants ofPseudomonas aeruginosatolerant to the action of trypsinsensitive aeruginocins can be readily isolated. They are found to be heterogeneous for a range of phenotypic characteristics (including the pattern of membrane protein components in polyacrylamide gel electrophoresis), response to bacteriophages (including both plaque formation and the ability to be lysogenized), sensitivity to various toxic agents, colonial morphology, and cellular morphology. The nature of these changes strongly supports the view that the mutants examined have undergone alteration in membrane structure. A limited genetic analysis indicates that at least two chromosomal regions are involved.
Protein and nucleic acid metabolism in organs from mice selected for larger and smaller body size
Authors: Priestley G. C. , Robertson Moira S. M. 
Published: September 2009

SUMMARYStudies of the growth and composition of Q-strain mice selected over 20 generations for high and low body weight at 6 weeks of age, and their unselected controls, were made on livers and kidneys of males from the five selection replicates A, B, C, D and F. Differences in growth rate between Large and Small QD mice were confirmed from 2 to 9 weeks of age, but were greatest in the third, fourth, sixth and seventh weeks. Total amounts of dry matter, protein, free amino acids, bulk RNA and ribosomes were increased or decreased from control values in proportion to organ weight. A less-perfect relationship between DNA content and organ weight suggested that some small changes in average cell mass had accompanied the main change in cell number in organs from the selected lines. Absorbance profiles of polyribosomes from both organs were identical in selected and control mice: selection had not operated on the proportion of single (currently inactive) ribosomes. Attempts to relate the observed differences in growth rate in QD mice to differences in the rate of protein synthesis produced an unexpected result: incorporation of radioactively labelled amino acids was consistently higher in the organs of the Small mice. Measurements of rates of protein turnover, and calculated rates of protein degradation, suggested that protein might also be degraded more rapidly in the small mice.
Replicated selection for body weight in mice
Authors: Falconer D. S. 
Published: September 2009

SUMMARYThe variation in the response to selection was studied by replication of selected lines. A random-bred strain of mice was divided into six replicates. Two-way selection for 6-week weight was applied in an identical manner to each replicate, and each had an unselected control. Each line (6 large, 6 control, 6 small) was maintained by minimal inbreeding with 8 single-pair matings. The overall mean responses, both up and down, were linear and very regular for ten generations, with realized heritabilities of 40% upwards, 33% downwards and 37% for the divergence. The separate replicates, however, differed greatly in their realized heritabilities, with upward selection ranging from 25 to 46%, and downward selection from 16 to 50%. The theoretical prediction that, because of genetic drift, the standard error of a realized heritability is underestimated by the standard error of the regression of response on cumulated selection differential was borne out in this experiment. The empirical standard error, calculated from the observed variance between replicates, was more than twice as great as that of the regression. The empirical standard errors showed that the asymmetry between upward and downward responses was not significant. The variation between the replicates was ascribed mainly to random drift, which may seriously influence the conclusions about the realized heritability and the asymmetry of response that would be drawn from a single experiment with the population size of one of these replicates. After 23 generations of selection the large lines were approaching limits, and the limit appeared to be at the same level in all. The small lines showed an undiminished realized heritability after 23 generations, but the selection differentials were then so small that little progress was made. There was evidence of counter-acting natural selection. All aspects of productivity – proportion of fertile matings, litter size and weaning rate – declined in the control lines. The overall productivity of the large lines was a little below the controls, and that of the small lines was reduced to about half the level of the controls. The separate replicates differed from each other significantly in all the components of productivity.
Lac+plasmids are responsible for the strong lactose-positive phenotype found in many strains ofKlebsiellaspecies
Authors: Reeve E. C. R. , Braithwaite J. A. 
Published: September 2009

SUMMARYA variety ofKlebsiellastrains examined all show either a strong (ML+) or a weak (ML−/+) lactose-positive phenotype on MacConkey agar. ML+Klebsiellae have about 10 times the β-galactosidase activity of ML−/+strains in cultures both induced and not induced for this enzyme. Of 14 ML+strains of diverse origin tested, at least 13 carry alacoperon on a plasmid which can be transferred toEscherichia coli. The seven plasmids so far studied in detail all belong to the F compatibility group but are unable to promote their own transfer. To explain these results it is suggested that theKlebsiellagroup derive from a common ancestor with a chromosomallacoperon of low efficiency, which was made good by the acquisition of alacoperon from another bacterial strain, probablyE. coli: the newlacgenes remained as a plasmid, possibly because they could not be integrated in the new host.
Simultaneous selection for two correlated traits inTribolium
Authors: Bell A. E. , Burris Martin J. 
Published: September 2009

SUMMARYSimultaneous selection byindependent culling levelsof two correlated traits in all four combinations of directions was investigated withTriboliumin a replicated experiment extending over nine generations. In addition to the two primary traits, 13-day larval weight and pupal weight, four secondary traits (pupation time, adult emergence time, adult weight and larval number) were observed.The observed responses for both selected and unselected traits agreed with theoretical expectations after the latter were adjusted for changes which occurred in genetic and phenotypic parameters. Phenotypio variances for the selected traits were correlated positively with population means, yet genetic variances and heritabilities declined in all selected populations. No change was detected in the genetic correlation between selected traits even though the divergent two-trait selection was designed especially to ‘break’ the positive correlation of + 0·55 ± 0·12 present in the base population.Striking changes in growth and developmental patterns resulting from the divergent selection were discussed in terms of metamorphic limits and ‘stabilizing’ genetic correlations.
Transfer-positive J-independent revertants of the F factor inEscherichia coliK 12
Authors: Achtman Mark 
Published: September 2009

SUMMARYCells carryingtraJ−mutants of F are transfer-deficient and are good recipients in conjugation (Achtman, Willets & Clark, 1972). In addition, thetraJgene product is involved in pilus- and in plasmid-specificity (Willetts, 1971). J-independent mutants were isolated as revertants of atraJ−mutant; they still carry thetraJ−mutation but also carry at least one other mutation which results in transfer in the absence of thetraJgene product. J-independent transfer of these mutants is not inhibited by the R 100 repressor. Various models are presented which can account for the properties oftraJ−mutants and of these J-independent revertants.
A multivariate analysis of subline divergence in the shape of the mandible in C57BL/Gr mice
Authors: Festing Michael 
Published: September 2009

SUMMARYThe shape of the mandible in. nine sublines of C57BL/Gr, seven other strains of ‘C57 ancestry’ and four unrelated strains was studied by multivariate techniques. The generalized distance function was used to classify individuals in the groups which they most closely resembled. The degree of misclassification depended on the pedigree relationship between strains and sublines. The generalized distance between pairs of subline centeroids was also highly correlated (r = 0·60) with the number of generations between them. A canonical variate analysis was used to reduce the dimensionality so that a graphical display of the relationships between strains and sublines could be made. The results agreed closely with the classification analysis. It was concluded that the shape of the mandible could be used for subline identification though the accuracy of this technique depends on how closely the sublines are related.
Non-homologous meiotic pairing in the A and B genomes of Brassica: its breeding significance in the production of variable amphidiploids
Authors: Prakash Shyam 
Published: September 2009

SUMMARYBrassica juncea Coss (2n = 36) is a naturally occurring allotetraploid. In the progenies of F1 hybrids of its constituent parents B. campestris sub.sp. oleifera var. toria × B. nigra and B. campestris sub.sp. japonica × B. nigra, the majority of the plants were parthenogenetic homozygous amphidiploids like B. juncea whereas a few differed in morphological and physiological characteristics. The latter, presumed to have arisen partheno-genetically, were suspected to be homozygous for chromosomes changed by allosyndetic recombination. One of these derived plants with curley leaves was crossed first with one of the homozygous amphidiploids and secondly with B. c. sub.sp. oleifera var. toria. Sporocytes of the two hybrids were studied at meiosis. The presence of one or two quadrivalents in the first hybrid and two trivalents in the second suggested that allosyndetic recombination had occurred in the 18-chromosome hybrid. The progeny was presumed to have arisen through pseudo-diploid parthenogenesis and this in association with allosyndetic recombination may provide a means of breeding higher yielding genotypes.
Location of factors enhancing crossing over on linkage group I of Neurospora
Authors: Hargrave Jenny , Threlkeld S. F. H. 
Published: September 2009

SUMMARYAn enhancement of cross-over frequencies previously reported by Newcombe & Threlkeld (1972) is shown to be due to two regions located on linkage group I, a few cross-over units to the right of the centromere. The distal region appears to be shorter than the proximal region, but equally effective in enhancing cross-over frequencies. The longer proximal region is readily divisable by cross-overs and probably spans several crossover units.
Characterization of the F transfer cistron,traL
Authors: Willetts N. S. 
Published: September 2009

SUMMARYThe properties of two transfer-deficient Flacmutants (inEscherichia coliK12) carrying mutations in the cistrontraLare described. ThetraLproduct is needed for conjugational DNA transfer and for pilus formation, but not for surface exclusion; it is not plasmid-specific.traLmaps betweentraAandtraE; one of thetraLmutations is apparently polar ontraA. The properties of Tra+revertants of this mutation suggest that thetraLproduct is directly required for F-specific phage infection.
The effects of inhibition of protein synthesis on the phenotype ofAbnormal-abdomen
Authors: Hillman Ralph , Shafer Stephen J. , Sang James H. 
Published: September 2009

SUMMARYPenetrance and expressivity of theDrosophilamutantAbnormal-abdomen(A53g) may be reduced by adding inhibitors of protein synthesis, of RNA synthesis, and of oxidative phosphorylation to the defined, sterile medium on which larvae are developing. When grown on regular diet, the mutant flies contain a higher concentration of total protein than do wild-type flies. The metabolic inhibitors which reduce the expressivity of the mutation also lower protein concentration in these mutant flies. The reduction of protein synthesis is directly correlated with the reduction of expression of the mutant genotype. The regulation of the morphological abdominal abnormalities by the complexA53ggenotype is discussed in relation to the control, by this same genetic system, of the mechanisms of protein synthesis.
Mixed self and random mating at two loci
Authors: Weir B. S. , Cockerham C. Clark 
Published: September 2009

SUMMARYAn infinite population practising a constant amount of selfing and random mating is studied. The effects of the mating system on two linked loci with an arbitrary number of neutral alleles are determined. Expressions are obtained for the two-locus descent measure, and hence genotypic frequencies and disequilibria functions, in any generation. The nature of the equilibrium population is deduced. The special cases of pure selfing or pure random mating and completely linked or completely unlinked loci are considered separately.
A new sex factor ofPseudomonas aeruginosa
Authors: Pemberton J. M. , Holloway B. W. 
Published: September 2009

SUMMARYOf 150 wild-type strains ofPseudomonas aeruginosaexamined, 48 formed recombinants when mated toP. aeruginosastrain PAO FP−and hence presumably possess sex factors. Three different types of sex factor were distinguished by the pattern of transfer of particular markers in different regions of the chromosome and by the ability to confer resistance to mercury in strain PAO. One new sex factor, FP39, was studied in detail, and while similar to the previously studied FP2 in terms of transfer kinetics, natural stability and resistance to curing by acridines, it differed from FP2 in promoting chromosome transfer from a site 10 min to the left of the FP2 origin and in showing apparently aberrant entry kinetics for a leucine marker situated 48 min from the FP2 origin. This was due to FP39 having a genetic determinant either for a structural gene of leucine biosynthesis or a specific suppressor gene for this locus. PAO strains carrying both FP2 and FP39 were unstable for both sex factors, suggesting a relationship between them.
Gene symbols inAspergillus nidulans
Authors: Clutterbuck A. J. 
Published: September 2009

SUMMARYProposals are made for symbols consisting of a primary gene symbol of lower case italic letters referring to the mutant phenotype (three letters for new symbols, old symbols unchanged), an italic capital locus specific letter (or a hyphen in mutants not yet tested for allelism) and an italic mutant number. Optional superscripts are recommended to convey additional information. Further proposals relate to symbols for chromosome aberrations and to strain numbers.
Comparison of two transformation systems for the assay of theNeurosporaphotoreactivating enzyme
Authors: Tuveson R. W. 
Published: September 2009

SUMMARYTheNeurospora crassaphotoreactivating enzyme has been assayed for by theHemophilus influenzaeandBacillus subtilistransformation systems. In contrast to theH. influenzaesystem, u.v.-treated transforming DNA fromB. subtilisdid not give evidence of reactivation of u.v. lesions by crude enzyme extracts fromN. crassawhen exposed to photoreactivating light. The u.v. dose required to inactivateB. subtilistransforming DNA is about ten times that required to inactivateH. influenzaeDNA to the same level of survival. This difference in dose required to inactivate DNA's of about the same base composition probably reflects the greater u.v. resistance of theB. subtilisrecipient strains used. Hypotheses are considered which suggest thatN. crassacrude enzyme extracts contain either nucleases which degradeB. subtilistransforming DNA excessively or an inhibitory factor which affects the transformation process itself.
Enzyme variability in theDrosophila willistoniGroup. V. Genic variation in natural populations ofDrosophila equinoxialis
Authors: Ayala Francisco J. , Powell Jeffrey R. , Tracey Martin L. 
Published: September 2009

SUMMARYWe have studied genetic variation at 27 loci in 42 samples from natural populations of a neotropical species,Drosophila equinoxialis, using standard techniques of starch-gel electrophoresis to detect allelic variation in genes coding for enzymes. There is considerarle genetic variability inD. equinoxialis. We have found allelic variation in each of the 27 loci, although not in every population. On the average, 71% of the loci are polymorphic – that is, the most common allele has a frequency no greater than 0·95 – in a given population. An individual is heterozygous on the average at 21·8% of its loci.The amount of genetic variation fluctuates widely from locus to locus. At theMdh-2locus arout 1% of the individuals are heterozygotes; at the other extreme more than 56% of the individuals are heterozygous at theEst-3. At any given locus the configuration of allelic frequencies is strikingly similar from locality to locality. At each and every locus the same allele is generally the most common throughout the distribution of the species. Yet differences in gene frequencies occur between localities. The pattern of genetic variation is incompatible with the hypothesis that the variation is adaptively neutral. Genetic variation inD. equinoxialisis maintained by balancing natural selection.The amount and pattern of genetic variation is similar inD. equinoxialisand its sibling species,D. willistoni. Yet the two species are genetically very different. Different sets of alleles occur at nearly 40% of the loci.
Experimental modification of the dominance relations of a melanotic tumour gene inDrosophila melanogaster
Authors: Belt Ann Louise , Burnet Barrie 
Published: September 2009

SUMMARYThe melanotic tumour genetu-C4inDrosophila melanogastershows incomplete dominance, together with variable penetrance and expressivity. It is tentatively located in the region of locus 52–53 on the third chromosome. Tumour formation in mutant homozygotes involves a precocious haemocyte transformation leading to the appearance of lamellocytes at the beginning of the third larval instar. These aggregate to form tumour-like masses which subsequently melanize. The process of tumour formation is in broad outline similar to that found in other tumour strains. Melanotic tumour formation is treated as a dichotomous threshold character, assuming an underlying normal distribution of liability relative to a fixed threshold. The expression of the tumour gene can be influenced by the levels of protein, phospholipid, nucleic acid and carbohydrate in the larval food medium, and changes in dominance and penetrance induced by sub-optimal environments deficient in these nutrients are positively correlated. Reinforcement by selection of the dominance relations oftu-C4was accompanied by correlated changes in penetrance. Conversely, selection for increased penetrance was accompanied by correlated changes in dominance. Dominance and penetrance, it is concluded, are fundamentally related aspects of tumour gene expression. Recruitment of dominance modifiers linked to the tumour gene was excluded by the mating scheme employed, and the observed changes in dominance relations in response to selection were due largely to modifiers located on the second chromosome. Changes in dominance relations produced by selection could be significantly reinforced, or reversed, by environmental factors and consequently show a substantial genotype – environment interaction effect. These facts are relevant to current theories of dominance evolution.
Chromosomal location of a prophage inPseudomonas aeruginosastrain PAO
Authors: Krishnapillai V. , Carey K. E. 
Published: September 2009

SUMMARYSegregation of the prophage of bacteriophage 90 has been observed in reciprocal crosses between lysogenic and non-lysogenic parents ofPseudomonas aeruginosastrain PAO. Linkage of the prophage was shown to three genes determining histidine biosynthesis in that region of the chromosome 7–13 min from the site on the chromosome at which the sex factor FP2 promotes chromosome mobilization.
Enzyme protein polymorphism in the slug Arion ater
Authors: Burnet Barrie 
Published: September 2009

SUMMARYPopulations of the slug Arion ater rufus sampled from several localities in England and the Netherlands are polymorphic for different electro-phoretic variants of digestive-gland esterase and salivary-gland tetra-zolium oxidase. Samples of Arion ater ater, which is endemic to the British Isles, were found to be monomorphic for these enzymes. Localized populations of A. a. rufus in Britain could have originated from specimens imported accidentally from continental Europe. There is evidence for gene flow between overlapping populations of the two subspecies. In one of the English populations of A. a. rufus, studied in detail, polymorphism for esterase and tetrazolium oxidase is shown to be balanced. Heterosis may be an important factor contributing to the maintenance of balanced polymorphism for tetrazolium oxidase in this population.
Evidence of premeiotic control of chromosome pairing inTriticum aestivum
Authors: Bayliss M. W. , Riley Ralph 
Published: September 2009

SUMMARYA genotype of wheat deficient for a pair of chromosomes stabilizing chiasma frequency against extremes of temperature was investigated to determine the position and duration of temperature sensitivity with respect to first metaphase of meiosis. Temperature changes over a critical range, followed by sequential sampling and measurement of chiasma frequency, showed a relatively short temperature-sensitive stage, the position and duration of which were dependent on the final temperature used. Comparison with meiotic timings made independently showed that the temperature-sensitive stage occurred in the premeiotic interphase. Euploid wheat was shown to have a stage in chiasma formation sensitive to high-temperature treatments at a similar time.Comparison with the work of others showed that the sensitive stage lay between the last premeiotic mitosis and the start of DNA synthesis. This modification of chromosome pairing at a much earlier stage than has been previously demonstrated is further evidence that the processes of chromosome pairing and crossing-over are probably more complex than formerly envisaged.