bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role oforiTintra-dependent enhanced recombination between mini-F-lac-oriTand λplac5
Authors: Carter Jeffrey R. , Patel Dipty R. , Porter Ronald D. 
Published: September 2009

SummaryRecombination between F42lacand λplac5is typically 20- to 50-fold more efficient than recombination between chromosomallacand λplac5. This enhancement of recombination isrecBCD-dependent and requires the expression of genes from thetraregulon of the F factor. Also required isoriT, the origin of F factor conjugational transfer, which must be located in-cisto the cellular copy oflac. In this study we show that enhanced recombination is not supported by anoriTpoint mutant that reducesoriTfunction in conjugation. We also present evidence that the activation oforiTfor recombination enhancement involves the same strand-specific nick that is required for conjugal DNA transfer. Although it is thought that the role oforiTin recombination enhancement is related to the facilitated entry of RecBCD enzyme into the DNA duplex, we were unable to detect any double-strand breakage atoriT.
Allelism tests of 15 dominant cataract mutations in mice
Authors: Kratochvilova J. , Favor J. 
Published: September 2009

SummaryFifteen autosomal dominant mutations that cause cataract of lenses in mice were tested for allelism. The outcrosses of double mutants revealed three allelism groups, consisting of 5, 4 and 2 mutations as well as 4 mutations which segregated independently. The results indicated 7 different cataract loci in the sample of 15 mutations. The biomicroscopic examination of the eyes showed that phenotypically similar as well as very distinct cataract mutations can be alleles of the same gene. Conversely, phenotypically similar mutations were shown to be non-allelic.
Phenotypic plasticity for life-history traits inDrosophila melanogaster. III. Effect of the environment on genetic parameters
Authors: Gebhardt M. D. , Stearns S. C. 
Published: September 2009

SummaryWe estimated genetic and environmental variance components for developmental time and dry weight at eclosion inDrosophila melanogasterraised in ten different environments (all combinations of 22, 25 and 28°C and 0·5, 1 and 4% yeast concentration, and 0·25% yeast at 25°C). We used six homozygous lines derived from a natural population for complete diallel crosses in each environment. Additive genetic variances were consistently low for both traits (h2around 10%). The additive genetic variance of developmental time was larger at lower yeast concentrations, but the heritability did not increase because other components were also larger. The additive genetic effects of the six parental lines changed ranks across environments, suggesting a mechanism for the maintenance of genetic variation in heterogenous environments.The variance due to non-directional dominance was small in most environments. However, there was directional dominance in the form of inbreeding depression for both traits. It was pronounced at high yeast levels and temperatures but disappeared when yeast or temperature were decreased. This meant that the heterozygous flies were more sensitive to environmental differences than homozygous flies. Because dominance effects are not heritable, this suggests that the evolution of plasticity can be constrained when dominance effects are important as a mechanism for plasticity.
Supernova(spno), a new maternal mutant producing variable-sized cleavage nuclei inDrosophila
Authors: Webster M. , Moretti P. , Brink N. G. 
Published: September 2009

SummaryThis paper describes a new recessive maternal lethal which disrupts normal nuclear division and migration during cleavage inDrosophila. We have named this gene locussupernova. Deletion mapping andin situhybridization have located this gene to 88 F9/89 A1 on the polytene chromosome map. The terminal mutant phenotype is characterized by the presence of many variable-sized nuclei scattered throughout the cytoplasm of the unhatched egg. Following fertilization, the initial cleavage divisions appear delayed and are often accompanied by the formation of ring-like association of chromosomes and/or chromosome bridges. Although the polymerization of tubulin into spindles occurs during the initial cleavage divisions, there appears to be both a spatial and temporal uncoupling of DNA replication from the formation and proper functioning of spindles. Eventually no functional spindles are formed, but nuclei continue to increase in size and number with increasing age of the embryo following fertilization.
The segregation ratio inwaxy-heterozygous barley plants
Authors: Frykman Ingrid , Bengtsson Bengt O. 
Published: September 2009

SummaryIn seven experiments the segregation ratio in barley plants heterozygous for thewaxy-gene was studied. Each experiment entailed the scoring of more than 40000 iodine-stained pollen grains from ten spikes. A significant over-representation of blue pollen grains was found in all experiments, with the segregation distortion (measured as a conversion force) ranging from 0·0063 to 0·0143. The distortion was unaffected by which of two mutations was used and which genetic background the plants had, but was stronger in 1988 than in 1987. Different statistical, methodological and biological explanations of the results are discussed.
Expression of theEscherichia coli ftsZgene: trials and tribulations of gene fusion studies
Authors: Robin Aline , D'Ari Richard 
Published: September 2009

SummaryTheftsZgene ofEscherichia coli, which codes for an essential cell division protein, is subjected to multiple regulation, as shown in part with studies using anftsZ::lacZoperon fusion located on phage λJFLIOO. Using this same fusion, we sought to isolate regulatory mutants overexpressingftsZby selecting mutants able to grow on lactose. One Lac+mutant was obtained which overexpressed theftsZ::lacZfusion 70-fold. The mutation responsible for the overexpression lies in a new gene,cot, located near 56 min on theE. coligenetic map. Thecotmutation probably affects the transcription of a chromosomal open reading frame, 0RF1, lying downstream of thebioAgene and adjacent to theftzZ::lacZfusion of the λJFL100 prophage integrated atattλ. Using anftsZ84(Ts) strain, in which there was a double selection for overexpression of bothftsZ::lacZandftsZ+, no Lac+Tr mutants were obtained from 3·6 × 1010bacteria; the introduction of amutLallele, increasing spontaneous base substitution mutation rates 75-fold, did not permit us to isolate such a mutant. We conclude that Lac+ftsZ-constitutive mutations cannot be obtained in λJFL100 lysogens by a single base substitution.
Adaptation and the ‘shifting balance’
Authors: Barton N. H. , Rouhani S. 
Published: September 2009

SummaryWright proposed that there is a ‘shifting balance’ between selection within demes, random drift, and selection between demes at different ‘adaptive peaks’. We investigate the establishment and spread of new adaptive peaks, considering a chromosome rearrangement, and a polygenic character under disruptive selection. When the number of migrants (Nm) is small, demes fluctuate independently, with a bias towards the fitter peak. WhenNmis large, the whole population can move to one of two stable equilibria, and so can be trapped near the lower peak. These two regimes are separated by a sharp transition at a criticalNmof order 1. Just below this critical point, adaptation is most efficient, since the shifting balance greatly increases the proportion of demes that reach the global optimum. This is so even if one peak is only slightly fitter than the other (ΔW≈1/N), and for both strong and weak selection (Ns(Ns ≪ 1 or Ns ≫ 1). Provided thatNmvaries sufficiently gradually from place to place, the fitter peak can be established in regions whereNm≈1, and can then spread through the rest of the range. Our analysis confirms Wright's argument that if selection, migration and drift are of the same order, the ‘shifting balance’ leads to efficient evolution towards the global optimum.
Properties of transgenic strains ofDrosophila melanogastercontaining I transposable elements fromDrosophila teissieri
Authors: Vaury Chantal , Pélisson Alain , Abad Pierre , Bucheton Alain 
Published: September 2009

SummaryI factors are transposable elements ofDrosophila melanogaster similarto mammalian LINEs, that transpose by reverse transcription of an RNA intermediate and are responsible for the I–R system of hybrid dysgenesis. There are two categories of strains in this species: inducer, that contain about 15 I elements at the various sites on chromosomal arms, and reactive, that lack active I factors. I elements occur in variousDrosophilaspecies. Potentially functional I factors fromDrosophila teissierican transpose when introduced by P-element-mediated transformation in a reactive strain ofDrosophila melanogaster. We have studied the properties ofDrosophila melanogasterstrains into which such an I factor fromDrosophila teissieri, namedItei, was introduced. Typical hybrid dysgenesis is produced when males carryingIteiare crossed with reactive females. However, more than one copy of the element seems necessary to produce dysgenic traits, whereas only one I factor ofDrosophila melanogasterseems to be sufficient. The copy number ofIteiin transformed lines maintained by endogamous crosses increases rapidly and stabilizes at values similar to those observed in inducer strains. AsDrosophila teissiericontains much fewer copies than theDrosophila melanogasterstrains, this suggests that the copy number of I elements is not simply regulated by sequences present in the element itself.
Spontaneous mutation for a quantitative trait inDrosophila melanogaster. II. Distribution of mutant effects on the trait and fitness
Authors: López Marí A. , López-Fanjul Carlos 
Published: September 2009

SummaryStarting from a completely homozygous population ofDrosophila melanogaster, lines have been derived and subjected to 47 generations of divergent selection for abdominal bristle number (20 lines selected in each direction) or to 60–67 generations of inbreeding (100 B lines maintained by a single brother-sister mating, 100 C lines maintained by two double first cousin ma tings). In the selected lines, 25 were identified carrying at least 30 mutations affecting bristle number. A large fraction of these mutations (42 %) were lethals. Non-lethal mutations had smaller effects on the trait, were predominantly additive and had no detectable pleiotropic effects on fitness. In the inbred lines, 21 mutations affecting bristles were individually analysed. Deleterious mutations had the largest effects on the trait (irrespective of sign) and showed recessive gene action (complete or incomplete). The rest were predominantly additive and had smaller effects. Thus, both procedures identify a quasi-neutral class of additive mutations which should be close to that responsible for standing variation in natural populations. Moreover, the results indicate a leptokurtic distribution of mutant effects, consistent with a model of natural selection acting on bristles through pleiotropic effects of pertinent loci on fitness. Consequently, neutral additive alleles of considerable effect can be found segregating at intermediate frequencies in natural populations.
The advance of Muller's ratchet in a haploid asexual population: approximate solutions based on diffusion theory
Authors: Stephan Wolfgang , Chao Lin , Smale Joanne Guna 
Published: September 2009

SummaryAsexual populations experiencing random genetic drift can accumulate an increasing number of deleterious mutations, a process called Muller's ratchet. We present here diffusion approximations for the rate at which Muller's ratchet advances in asexual haploid populations. The most important parameter of this process isn0=N e−U/s, whereNis population size,Uthe genomic mutation rate andsthe selection coefficient. In a very large population,n0is the equilibrium size of the mutation-free class. We examined the casen0> 1 and developed one approximation for intermediate values ofNandsand one for large values ofNands. For intermediate values, the expected time at which the ratchet advances increases linearly withn0. For large values, the time increases in a more or less exponential fashion withn0. In addition ton0,sis also an important determinant of the speed of the ratchet. IfNandsare intermediate andn0is fixed, we find that increasingsaccelerates the ratchet. In contrast, for a givenn0, but largeNands, increasingsslows the ratchet. Except whensis small, results based on our approximations fit well those from computer simulations.
Mutability, sterility and suppression in P—M hybrid dysgenesis: the influence ofPsubline, cross, chromosome, sex and P-element structure
Authors: Wang Yuan , Balter Howard , Levitan Max , Margulies Lola 
Published: September 2009

SummaryThree Harwich P sublines with differentP-element activity potential were used to investigate the influence of P-derived chromosomes on snωmutability andvgsuppression and to relate the induction of these dysgenic traits to the number and structure ofPelements. Destabilization of thesnωallele, a measure ofPtransposase activity, was differentially influenced by the major autosomes. Chromosome 2 of the standard Harwich subline, Hw, induced only 60% of the level of mutability relative to chromosome 3, whereas chromosome 3 of the weakest Harwich subline, Hf, induced only 50% of the mutability relative to chromosome 2. In somatic suppression of thevg21–3allele, chromosome 3 of the Hfsubline produced a lower level of complete suppression as compared to chromosome 3 of the Hwor the Hssubline (the high hybrid-dysgenesis-inducing subline). The level of these dysgenic traits and GD sterility, was not correlated with the number ofPelements per individual (67–68) or per chromosome arm which was very similar among the sublines. The number of completePelements per genome, based on Southern blot analysis of the X and major autosomes, ranged from 15 to 19. Destabilization of thesnωallele andvgsuppression by chromosome 3 was correlated with a greater number of completePelements. Two novel unexpected observations emerged from these studies: bothsnωmutability andvgsuppression data demonstrated highP-element activity in hybrids derived from non-dysgenic crosses irrespective of Harwich subline, indicating a lack of P-cytotype regulation. Mutability in non-dysgenic males ranged from 40 to 60% of the level found in dysgenic males. The highsnωmutability and low GD sterility in non-dysgenic hybrids suggests that these traits may arise by a different mechanism.
Parental imprinting on the mouse X chromosome: effects on the early development of X0, XXY and XXX embryos
Authors: Tada Takashi , Takagi Nobuo , Adler Ilse-Dore 
Published: September 2009

SummaryTo examine the effects of X-chromosome imprinting during early mouse embryogenesis, we attempted to produce XM0, Xp0, XMXMY, XMXPY and XMXMXP(where XMand Xpstand for the maternally and the paternally derived X chromosome, respectively) making use of mouse strains bearing the translocation Rb(X.2)2Ad and the inversion In(X)1H. Unlike XMXPY embryos, XMXMY and XMXMXPconceptuses suffered from severe growth retardation or abnormal development characterized by deficient extra-embryonic structures at 6.5–7.5 days post coitum (dpc). A cytogenetic study suggested that two XMchromosomes remaining active in certain non-epiblast cells were responsible for the serious developmental abnormality found in these embryos disomic for XM. Although matings involving females heterozygous for Rb(X.2)2Ad hinted at the paucity of XP0 embryos relative to those having the complementary karyotype of XMXMXP, further study of embryos from matings between females heterozygous for In(X)1H and Rb2Ad males did not substantiate this observation. Thus, the extensive peri-implantation loss of XP0 embryos shown by Hunt (1991) may be confined to XO mothers. Taken together, this study failed to reveal a parentally imprinted X-linked gene essential for early mouse embryogenesis other than the one most probably corresponding to the X-chromosome inactivation centre.
The genetic basis of response in mouse lines divergently selected for body weight or fat content. II. The contribution of genes with a large effect
Authors: Veerkamp Roel F. , Haley Chris S. , Knott Sara A. , Hastings Ian M. 
Published: September 2009

SummaryGene action underlying selection responses has been studied using crossbreeding. Maximum likelihood based segregation analysis has been presented for analysing backcross data for the presence of genes with a large effect. Two sets of divergently selected lines (P-lines for body weight and F-lines for fat content) were reciprocally crossed and the F1s were crossed to the high and low lines to produce all possible backcrosses. Earlier analysis had shown that the difference in body weight at 10 weeks (n= 595) between the high and low P-lines was largely (75–80%) explained by autosomal, additive genes with the remainder explained by additive genes on the X chromosome. Maximum likelihood segregation analysis suggested the presence of a major effect on the X chromosome, but as there was only one round of recombination between the X chromosomes in the forming of the backcrosses, linked genes on the X chromosome could have acted together to give the appearance of a single major gene. The difference in fat content between the F-lines (n= 578) could be explained by autosomal genes of largely additive effect. Segregation analysis suggested the presence of a major gene with complete dominance, but this was attributed to a relationship between the mean and the variance: transformation of the data resulted in only polygenic additive genes being of importance. This study concluded that maximum likelihood based analysis and crosses between selected lines provide a powerful means for studying the gene action underlying responses to selection.
Constitutive magnification by theYbb−chromosome ofDrosophila melanogaster
Authors: Komma Donald J. , Glass Susan J. , Endow Sharyn A. 
Published: September 2009

SummaryYbb−is an rDNA-deficient chromosome of Drosophila that has often been used in magnification experiments to induce high-frequency reversion ofbobbed(bb) chromosomes. We observed previously thatYbb−causes ring chromosome loss even when the rings arebb+, suggesting thatYbb−induces magnifying sister chromatid exchanges inbb+rings. Here we show that theYbb-chromosome causes low levels of bb magnification inbb+flies. We refer to the ability ofYbb−to bypass the rDNA deficiency requirement for magnification as ‘constitutive’ magnification. We have magnified the ribosomal genes on theYbb−chromosome and analysed the revertant chromosomes using genetic and molecular methods. We find that magnifiedYbb−chromosomes also exhibit constitutive magnifier activity. Molecular analysis shows that both type 1 and type 2 intron+ribosomal gene repeats are associated with magnifiedYbb−chromosomes. Type 2 introns have been described previously in the rDNA of bothXandYchromosomes. However, type 1 intervening sequences are thought to be present only inX, but notY, ribosomal genes. Some of theYbb−type 1 insertions differ from those present in the rDNA ofXchromosomes in that they contain anEcoRl site, and some may be present in tandem arrays. The constitutive magnifier activity ofYbb−may reside either in the structurally unusual ribosomal gene intervening sequences associated with the chromosome, or in the locus onYLthat is required for magnification to occur.
Analysis of distributions of single-locus heterozygosity as a test of neutral theory
Authors: Woodwark M. , Skibinski D. O. F. , Ward R. D. 
Published: September 2009

SummaryThree tests of neutral theory were carried out using a large dataset of vertebrate allozyme studies. The first test considered the relationship between the mean and variance of single locus heterozygosity across a sample of enzymes and non-enzymatic proteins. The second test compared the distributions of heterozygosity between paired proteins in balanced datasets in which each protein is scored for the same sample of species. The third test compared the observed distribution of single locus heterozygosity with theoretical distributions predicted by neutral theory. The results show an excellent quantitative fit with the predictions of neutral theory, though some small deviations from neutrality were observed which are consistent with the action of natural selection.
The molecular basis of instability of thesingedvery weakmutation inDrosophila melanogaster
Authors: Ortori C. A. , Chambers D. , Brookfield J. F. Y. 
Published: September 2009

SummaryThesingedvery weakmutation was created by the sequential addition of two P transposable elements to thesingedgene. The mutation can be somatically unstable through the action of a dominant maternal effect mutation on the second chromosome. It is also unstable in the germ line in these conditions. Sequencing of the region of the P insertions in the mutation reveals that the two inserted elements have single internal deletions, and the larger of the two is a copy of the KP element. The mutation will generate, at high frequencies, stronglysingedand pseudo-wild type products by reversions occurred in the germline. These are the result of the precise excision of the smaller and the larger elements respectively. By PCR amplification of dissected thoraces we show that the somatic instability of the mutation, from a weak to a strongsingedphenotype, is also caused by the excision of the smaller of the two elements.
Differential regulation ofPandhobomobile elements by two laboratory strains ofDrosophila melanogaster
Authors: Yannopoulos George , Zabalou Sophia , Stamatis Nikos , Tsamathis George 
Published: September 2009

SummaryAnalysis of the transposition behaviour of thePandhoboelements borne by the31·1/CyL4MRF (P), 23·5Δ/CyL4MRF (hobo)and23·5*/Cy MRF (hobo)strains in the progeny of dysgenic crosses with two ME laboratory strains (Berlin-k and dp b en bw) at 25 °C revealed that: (a) the two ME laboratory strains affect differently the transposition rates ofPandhoboelements. More precisely,Pelement transposition is higher in heterozygotes withdp b en bwthan in those withBerlin-k. In contrast, the transposition rate ofhoboelements is higher inBerlin-kthan indp b cn bwheterozygotes. (b) LikeP, hobohas the potential to transpose at high frequencies and to nonhomologous chromosomes, (c) The dysgenically inactivehoboelements of the3·11 MRFstrain transpose more frequently than the dysgenically activehoboelements of the23·5 MRFstrains in certain crosses, (d) There are insertion hot spots forPandhoboelements. For thePelements there are enough data to suggest that the insertion hot spots are different in the two EM strains. The data are discussed on the basis of the involvement of putative host factors in transposition regulation of thePandhoboelements.
Phenotypic expression of the fused (Fu) gene in chimaeric mice
Authors: Redina Olga E. , Zhelezova Antonina I. , Golubitsa Alevtina N. , Agulnik Alexander I. , Ruvinsky Anatoly O. 
Published: September 2009

SummaryThe dominant gene Fused (Fu) produces skeletal abnormalities during embryonic development. It was previously shown that C57BL/6 mice contain a suppressor ofFu, which acts after fertilization. Chimaeras were used to study whether this gene would suppress theFuphenotype after the 8-cell stage of embryo development. We found no effect of the suppressor gene onFuphenotype (its degree and frequency of expression) in chimaeric mice. We conclude that either the suppressor gene from C57BL/6 mice can only influenceFuexpression at the intracellular level orFuexpression is determined before the 8-cell embryonic stage.