bluuebunny/crossref_metadata_2025_split huggingface dataset:
The lactose system inKlebsiella aerogenesV9A 2. Galactoside permeases which accumulate lactose or melibiose
Authors: Reeve E. C. R. , Braithwaite J. A. 
Published: September 2009

SUMMARYKlebsiella aerogenesV9A possesses at least three galactoside permeases, the lactose permease (LacP), the melibiose permease (MelP) and a third permease (GPIII), and also a galactose permease. It is shown that the first three of these permeases all accumulate both lactose and melibiose efficiently, while the galactose permease takes up neither sugar. Lactose only induces LacP and melibiose only induces MelP.d-fucose, isopropyl-β-d-thiogalactoside (IPTG) and methyl-β-d-thiogalactoside (TMG) all induce GPIII, but galactose does not. GPIII takes up both lactose and melibiose but cannot accumulate lactose in the presence of IPTG. Thus substantial differences are found between the galactoside permeases ofKlebsiellaandEscherichia coli.
Isolation of a transducing phage forming plaques onPseudomonas maltophiliaandPseudomonas aeruginosa
Authors: Moillo Agnès M. 
Published: September 2009

SUMMARYA temperate phage, M6, has been isolated from a lysogenic strain ofPseudomonas maltophilia. An extended range mutant, M6a, plates onP. aeruginosaand is capable of general transduction in this species. This phage may be of value for comparing the genetic maps of different species ofPseudomonas.
Fixation time of overdominant alleles influenced by random fluctuation of selection intensity
Authors: Ohta Tomoko , Kimura Motoo 
Published: September 2009

SUMMARYIt was demonstrated that the number of generations until fixation or loss of an overdominant alleles is influenced by random fluctuation of selection coefficients. When 2<Vs, whereis the mean selection coefficient against either homozygote andVsis the between -generation variance of the selection coefficient, overdominance generally accelerates rather than retards fixation of segregating alleles. This finding should have important bearing on our consideration of the behaviour of polymorphic variants which are nearly neutral but have very slight overdominance. When the population size (Ne) is extremely large, not onlyNebut also/Vshave to be considered in discussing the effectiveness of overdominance.
Segregation of co-transduced streptomycin and tetracycline resistance in Staphylococcus aureus
Authors: Grubb W. B. , O'Reilly R. J. , May J. W. 
Published: September 2009

SUMMARYExtrachromosomal streptomycin and tetracycline resistance in Staphylococcus aureus E169 has been transduced to three different recipients. An analysis of the transductants demonstrates that: (1) in most cases the behaviour of the markers in the transductants is similar to that in the donor; (2) the markers are co-transduced at frequencies of 2–44% and the frequency is highest when the selected marker is streptomycin resistance; (3) in the co-transductants the markers segregate independently, suggesting that they are unlinked.
A genetic map of several mutations affecting the mucopeptide layer ofEscherichia coli
Authors: Wijsman H. J. W. 
Published: September 2009

SUMMARYSeveral temperature-sensitive mutants ofEscherichia coliwere isolated which lyse at the restrictive temperature. Some of these possess a biochemically defined lesion in cell-wall mucopeptide synthesis. Three genes, termedmurC, EandF, have been localized between theaziandleumarkers. From transductional data a fine structure map was constructed of themurmutations, establishing the order of the genes. The genetic relationship between these cell wall genes and neighbouring genes involved in cell division is discussed.
Chromosome translocations inGlossina austeni
Authors: Curtis C. F. , Southern D. I. , Pell P. E. , Craig-Cameron T. A. 
Published: September 2009

SUMMARYAn autosomal translocation in the tsetse flyGlossina austeniwas studied genetically, cytogenetically and for its effects on viability. Flies homo-zygous for the structural change could be identified by outcrossing to wild-type and demonstrating semi-sterility in all the progeny.A cytogenetical analysis of male meioses in samples of pupae which were sibs of the semi-sterile progeny showed them to be structurally heterozygous for the translocation. Matings of the translocation heterozygotes and homozygotes gave the expected progeny ratios, with the exception of a deficit of females classified as translocation homozygotes. This was due to their sterility or inviability. Those female homozygotes which did breed showed a subnormal lifetime pupal production. These deleterious recessive effects were probably due to the translocation itself although the influence of linked loci could not be ruled out. These effects would prevent the mass rearing of this particular translocation for a tesetse control project.Two other stocks which showed semi-sterility were found to carry autosomal translocations and two which currently showed holandric inheritance haveY-autosome translocations. One stock with holandric inheritance of extreme sterility carries a double translocation involving two autosomes and theYchromosome.
Some invariant properties of a geographically structured finite population: distribution of heterozygotes under irreversible mutation
Authors: Maruyama Takeo 
Published: September 2009

SUMMARYIt is shown that the distribution of the sum of heterozygotes, due to mutant gene(s), that appear in a finite population is invariant under geographical structure, provided that the mutant gene has additive effect on fitness and migration does not change the genetic constitution as a whole population. The expected number of heterozygotes is 2N when Ns = 0 and gradually rises to 4N as Ns increases provided s remains small, where N = the total population size and s = selective advantage of a mutant gene. The distribution of the heterozygosity summed over those generations in which the gene frequency in the entire population is specified, is also shown to be invariant. In the case of a neutral mutant, the density is equal to 4(1 − Y) where Y is the frequency of the mutant in the whole population, and in the selectively advantageous case, it is approximately equal to a constant function 4, provided that the population size times selection coefficient is sufficiently large. These quantities conditional on the fixation of the mutant are shown to be invariant and some special cases are obtained explicitly.
The lactose system inKlebsiella aerogenesV9A: 1. Characteristics of two Lac mutant phenotypes which revert to wild-type
Authors: Reeve E. C. R. , Braithwaite J. A. 
Published: September 2009

SUMMARYA wild strain ofKlebsiella aerogenes(V9A), which contains a plasmid Fklaccarrying the genes of thelacoperon, gives two mutant cell types, recognized by the appearance of their colonies on MacConkey lactose agar. These are referred to as ML−and ML−/+, wild-type being ML+. ML−cells can grow rapidly on 1% lactose as carbon source but very slowly on 0·2% unless induced by TMG or D-fucose, or by previous growth on galactose, melibiose or raffinose, which enables them to grow rapidly on 0·2% lactose for 2–4 cell generations. Previous growth on 1% lactose does not induce the ability to grow rapidly on 0·2% lactose. It is concluded that ML−cells have a defect in the lactose permease gene which allows slow uptake of lactose when the external concentration is 0·2% and more rapid uptake when the external concentration is increased. In addition, TMG, D-fucose, galactose, melibiose and raffinose induce one or more other galactoside permeases which can accumulate lactose efficiently but are not induced by lactose. ML−/+cells can grow normally on 0·2% lactose as carbon source, but only after a substantial lag when transferred from glucose, glycerol or sucrose, and after an even longer lag when transferred from melibiose or raffinose. Wild-type cells (ML+) grow normally on 0·2% lactose after a short lag of less than a cell generation time, when transferred from any other carbon source. Cells of each of the three phenotypes (+, −/+ and −) can mutate to give both of the other two phenotypes. Incomplete genetic evidence suggests that the ML−mutation is a result of a reversible change in the Fklacplasmid.
An analysis of temperature-dependent asynapsis inTriticum aestivum
Authors: Bayliss M. W. , Riley Ralph 
Published: September 2009

SUMMARYMeasurements of chiasma frequency over a range of temperatures from 9 to 35 °C in euploid wheat and lines nullisomic for chromosome 5D showed the absence of chromosome 5D greatly to increase the sensitivity of chiasma frequency to temperature, resulting in complete univalence at the lowest temperatures. Careful examination of meiotic prophase showed the lowering of chiasma frequency to be correlated with failure of zygotene chromosome pairing, justifying the use of the term asynaptic. Observation of the pairing behaviour of an isochromosome in the nullisomic 5D background suggested that the asynapsis was due to a failure in the mechanism of chromosome pairing rather than of the pre-alignment of homologues. The observed effects in the absence of chromosome 5D could be due to the presence of a recessive allele at the locus of chromosome 5A, also known to control stability of chiasma frequency to temperature. In conclusion it is pointed out that in euploid wheat the sensitivity of chiasma frequency to temperatures within the normal meteorological range could influence the cytological stability of the wheat crop.
A possible source of primary nucleotide chain breaks in recombinant structures in eukaryotes
Authors: Hastings P. J. 
Published: September 2009

SUMMARYIt is argued that the primary break-points for meiotic recombination arise from the replication of regions in which DNA synthesis is delayed until meiotic prophase. The gaps would be in nucleotide chains of opposite polarity in sister chromatids. This would place a restriction on the recombination models of Holliday and of Whitehouse, so that neither is able to explain observed chromatid interference. It follows that if the primary breaks originate in the manner proposed here, the Whitehouse and Holliday models are either both wrong or both right.
Unusual recombination values and the mapping of the lethal miniature in the house mouse
Authors: Wallace Margaret E. , Mallyon S. A. 
Published: September 2009

SUMMARYData are presented from a balanced backcross experiment involving three linkage group VI markers in the house mouse. These establish the order N–Ca–bt (naked–caracul–belted), and confirm the unusual recombination values reported earlier; the values for male heterozygotes are about 4 times those for the female ones. The linkage group is extended by the linkage of miniature, mn, with N and Ca, here reported. Data are given which establish the order mn–N–Ca–bt; they indicate that the recombination values for males may be greater than those for females for some way to the left of the N–Ca–bt segment.
The characterization of an alanine racemase mutant ofEscherichia coli
Authors: Wijsman H. J. W. 
Published: September 2009

SUMMARYAmong temperature-sensitive mutants ofEscherichia colia strain was discovered requiring D-alanine for growth. It was proved to possess an altered alanine racemase. The structural gene for this enzyme, designatedalr, is located betweenmetBandpur A. The properties of the enzyme and its locus suggest that it is not under control of the mechanisms which regulate mucopeptide formation. A suppressor of thealrmutation was discovered neartrp, and termedmsuA.
The relationship between the transfer systems of some bacterial plasmids
Authors: Alfaro Guillermo , Willetts Neil 
Published: September 2009

SUMMARYThe relationship between the transfer systems of several plasmids was investigated, using as criteria complementation of a series of transfer-deficientFlacmutants, the efficiency of plating of F-specific phages, and identification of surface exclusion systems. The transfer systems of ColV2 and ColVBtrpwere similar to that of F except for surface exclusion: ColVBtrpspecified a surface exclusion system different from that of F, and ColV2 did not specify any detectable system. The transfer system of R1–19 was also similar to that of Flac, but the products oftraA,traIandtraJwere plasmid-specific. R1–19 determined the same surface exclusion system as ColVBtrp, and this was under the control of the transfer inhibitor. The transfer systems of ColIbdrdandFlacwere unrelated. ColEl was transferred byFlac traI−mutants, but not by mutants in other cistrons.
Sex-linked variegation modified by selection in brindled mice
Authors: Falconer D. S. , Isaacson J. H. 
Published: September 2009

SUMMARYThe sex-linked gene,brindled, in the mouse produces a coat-colour variegation in heterozygous females. There is much individual variation in the relative areas of mutant and wild-type colour, but it was not known if any of this variation was genetic. The main object, when the experiments were started, was to test the simple expectation of the Lyon hypothesis, that ifX-inactivation is random the variegation should not be modifiable by selection. On the assumption that the variegation is due toX-chromosome inactivation, modification by selection would show that the inactivation process, or some property of the derived cell populations, is under genetic control. Heterozygous females were accordingly selected for the area of coat showing the mutant colour. Selection based on individual phenotypes was ineffective, but four cycles of reciprocal recurrent selection based on progeny-means produced a ‘High’ line with 64% mutant area and a ‘Low’ line with 30% mutant area, from a base population with 53% mutant area. Autosomal modifiers were not responsible for the response; the difference between the selected lines was entirely due to properties of theXchromosomes carrying thebrindledgene. The changed properties of theXchromosomes were not restricted to the locus ofbrindled, but extended at least as far as the locus oftabby. The chromosomes carrying the wild-type allele ofbrindledwere not altered by the selection, but normalXchromosomes from other strains affected the degree of variegation. It was concluded that the difference between the selected lines was due either to non-random inactivation or to somatic cell selection. It was not possible to distinguish between these two mechanisms. The results obtained in these experiments with a structurally normalXchromosome were in all essentials similar to those obtained by Cattanach with hisX-autosome translocation.
Long-term selection for a quantitative character in large replicate populations ofDrosophila melanogaster: 1. Response to selection
Authors: Yoo B. H. 
Published: September 2009

SUMMARYThe response to long-term selection for increased abdominal bristle number was studied in six replicate lines ofDrosophila melanogasterderived from thescCanberra outbred strain. Each line was continued for 86–89 generations with 50 pairs of parents selected at an intensity of 20%, and subsequently for 32–35 generations without selection. Response continued for at least 75 generations and average total response was in excess of 36 additive genetic standard deviations of the base population (σA) or 51 times the response in the first generation. The pattern of longterm response was diverse and unpredictable typically with one or more accelerated responses in later generations. At termination of the selection, most of the replicate lines were extremely unstable with high phenotypic variability, and lost much of their genetic gains rapidly upon relaxation of selection.The variation in response among replicates rose in the early phase of selection to level off at approximately 7·6around generation 25. As some lines plateaued, it increased further to a level higher than would be accommodated by most genetic models. The replicate variation was even higher after many generations of relaxed selection. The genetic diversity among replicates, as revealed in total response, the individuality of response patterns and variation of the sex-dimorphism ratio, suggests that abdominal bristle number is influenced potentially by a large number of genes, but a smaller subset of them was responsible for selection response in any one line.
Long-term selection for a quantitative character in large replicate populations ofDrosophila melanogaster: II. Lethals and visible mutants with large effects
Authors: Yoo B. H. 
Published: September 2009

SUMMARYLethal frequencies on the second and third chromosomes were estimated three times in six replicate lines ofDrosophila melanogasterselected for increased abdominal bristle number, at G 14–16, G 37–44 and G 79. Ten lethals were detected at a frequency of about 5% or higher at G 14–16, of which only one recurred in subsequent tests. Another ten lethals which had not been detected previously were found at G 37–44, and the 5 most frequent ones recurred at G 79. In the last test, 15 presumably new lethals were detected, of which at least 4 appeared well established. In addition, six reversions (fromsctosc+), a new mutant at the scute locus andscawere discovered. The effects on the selected character of some lethals and visible mutants were large and variable, but not always sufficient to explain the observed frequencies. The major lethals detected at G 37–44 and G 79 for the first time were most probably ‘mutations’ (in the broad sense) which occurred during selection. The likely origins of such ‘mutations’ were discussed, with a suggestion that the known mutation rate for recessive lethals would not be incompatible with the observed frequency of occurrence of the ‘mutations’.
Size of population required for artificial selection
Authors: Nicholas F. W. 
Published: September 2009

SUMMARYIt is widely acknowledged that genetic drift is an important source of variation in response to artificial directional selection. How large should a selection line be in order to reduce the effect of genetic drift to an acceptably low level?This paper investigates two criteria that can be used to answer this question in relation to short-term response to selection. The first criterion is coefficient of variation of response, and the second criterion is chance of success, where a successful selection programme is one in which the observed response is greater than a certain proportion, β, of expected response.For a simple mass selection programme with intensityiand heritabilityh2, the size of population required in order for the coefficient of variation of response to be γ aftertgenerations, is approximately 2/(γih)2t, and the size required for the chance of success to be α aftertgenerations is approximately 2{zα/(β−l)ih}2/t, wherezαis the standard normal deviate corresponding to the probability α.As an example, suppose it is required that aftertgenerations the coefficient of variation of response be 10% or that there be a 90% chance of achieving at least 9/10 of expected response. Sinceih≤ 2 in most selection programmes, the size of population required is at least 50/tor 82/trespectively. Ifih≤ 1, the corresponding sizes are 200/tand 328/t.Results are extended to enable the calculation of size of population required for any type of artificial directional selection programme, including those in which generations overlap.
Genic determination of the autogamy trait in the hypotrich ciliate,Euplotes crassus
Authors: Dini Fernando , Luporini Pierangelo 
Published: September 2009

SUMMARYCross-fertilizing stocks ofEuplotes crassus, differing as to the ability to undergo autogamy, were subjected to breeding analysis. The resulting data are consistent with the interpretation that a single locus (a) with a pair of alleles (a+;a−) controls the ability to undergo autogamy. The two alleles express a simple dominance relationship in which the dominant allele (a+) permits expression of the autogamy trait. Cross-breeding experiments also suggest that thealocus is not linked to themtlocus which determines the mating-type trait.
Chromosomal change and rectangular evolution in North American cyprinid fishes
Authors: Gold J. R. 
Published: September 2009

SUMMARYAn important question in evolutionary biology concerns the manner and tempo in which organismal and/or genetic changes that promote evolutionary divergence occur. One recent hypothesis, termedrectangular evolution, holds that most significant evolutionary change occurs during occasional or periodic speciation episodes, with long periods of evolutionary stability in the interim. An alternative view, termedphyletic gradualism, holds that evolutionary divergences proceed by the slow and even accumulation of genetic differences within populations of established species. Two brief tests of rectangular evolution are presented using chromosomal data from North American cyprinid fishes (minnows), a group known to have experienced heterogeneous rates of splitting. Within the rapidly speciated genusNotropis, rates of chromosomal evolution appear slower relative to other, less rapidly speciated confamilial genera. Species ofNotropisalso are less divergent chromosomally, on the average, than are species from other cyprinid genera. These results are in compatible with a rectangular mode of chromosomal divergence these fishes. The results also reveal inconsistencies with a gradual mode chromosomal divergence, but at present this hypothesis cannot be falsified. Consideration of these and other data suggests that different levels of the cyprinid genome may follow independent evolutionary paths.
T(16: 17)43H translocation as a tool in analysis of the proximal part of chromosome 17 (including T-t gene complex) of the mouse
Authors: Forejt Jiří , Čapková Jana , Gregorová Soňa 
Published: September 2009

SUMMARYLinkage relationships of three gene markers of chromosome 17, namely Brachyury (T), tufted (tf), and Histocompatibility-2 (H-2), to the break-point of T(16; 17)43H male sterile translocation were established. The following order was found: T−tf−T43H−H-2. In all cases the translocation break was found in cis to H-2k, haplotype, no recombinant being found among 218 backcross individuals examined. More than 60 viable and fertile animals trisomic for the proximal part of chromosome 17 (including T-t genetic complex) have been recovered among progeny of T43H/+ female translocation heterozygotes as a result of adjacent −2 disjunction at first meiotic division. Mutation tf has been assigned to band 17B in chromosome 17 by comparing the location of T190Ca and T43H genetic and cytological breakpoints. Recombination between centromere 17 and T43H break was reduced almost to zero in the presence of Rb(16.17)7Bnr translocation. The unexpected restoration of male fertility was observed in T43H/Rb7Bnr hybrids (T43H/+ males being completely sterile) which made it possible to prepare the first homozygotes for T43H male–sterile translocation. Direct estimation of chiasma frequencies in centromere 17−T43H region indicated an 11 cM distance between the centromere 17 and the proximal end of t12 haplotype. The significance of centromere −t (or H-2) distance on the predictable restrictions of the possible haploid manifestation of T-t or H-2 gene products on sperm membrane is discussed.
Sex differences in fitness and selection for centric fusions between sex-chromosomes and autosomes
Authors: Charlesworth D. , Charlesworth B. 
Published: September 2009

SUMMARYA model of centric fusions between theXorYchromosome and an autosome carrying a selected locus is studied. It is assumed that fusions are not associated with any fitness effects, and that all chromosomes disjoin regularly from their homologues. It is shown that a necessary condition for the fusion to be favoured is that there is a selectively maintained sex difference in allele frequencies at the selected locus. If this condition is satisfied, the initial rate of increase of a rareY-autosome fusion is about three times that of anX-autosome fusion, with the same parameter values. Computer calculations of the final equilibrium states reached by populations containing such fusions were done.