bluuebunny/crossref_metadata_2025_split huggingface dataset:
Increased intragenic recombination and non-disjunction in the Rec-1 strain ofCaenorhabditis elegans
Authors: Rattray B. , Rose A. M. 
Published: September 2009

SummaryThe Rec-1 strain ofCaenorhabditis elegansincreases recombination frequency three-fold. In this paper, we have investigated the effect of Rec-1 on the intragenic recombination phenomena of crossing-over and gene conversion. These events were increased two- to three-fold as wasX-chromosome non-disjunction. All of the recovered recombinants were independent events, indicating that Rec-1 does not act pre-meiotically. The pattern of recombination in the Rec-1 strain resembles a meiotic pattern more than a radiation expansion. We conclude from this result that the Rec-1 enhancement of recombination is not the result of an increased number of DNA lesions randomly distributed along the chromosome. The increased recombination frequency of Rec-1 was not accompanied by any detrimental effects on growth, progeny number or spontaneous mutation rate. In this regard, the results may have implications for models which propose either selective advantage or disadvantage accompanying increased recombination.
The relationship between position and expression of genes on the kangarooXchromosome suggests a tissue-specific spread of inactivation from a single control site
Authors: Graves Jennifer A. Marshall , Dawson Garey W. 
Published: September 2009

SummaryIn marsupials,Xchromosome inactivation is paternal and incomplete. The tissue-specific pattern of inactivation ofX-linked loci (G6PD, PGK, GLA) has been attributed to a piecemeal inactivation of different regions of theX. We here propose an alternative hypothesis, in which inactivation of the marsupialXis a chromosome-wide event, but is differentially regulated in different tissues. This hypothesis was suggested by the relationship between the positions and activity of genes on the kangaroo paternalX. In the absence of an HPRT polymorphism, we have used somatic cell hybridization to assess the activity of the paternal HPRT allele in lymphocytes and fibroblasts. The absence of the paternalX, and of the paternal forms of G6PD or PGK, from 33 cell hybrids made by fusing HPRT-deficient rodent cells with lymphocytes or fibroblasts of heterozygous females, suggests that the HPRT gene on the paternalXis inactive in both tissues and therefore not selectable. Since HPRT is located medially on theXqnear GLA, which shares the same characteristics of activity, we suggest that the locus-specific and tissue-specific patterns of activity result from a differential spread of inactivation from a single control locus, located near HPRT and GLA, outwards in both directions to G6PD and PGK. The nucleolus organizer region on the short arm does not seem to be part of the inactivated unit.
Three newt-haplotypes ofMus musculusreveal structural similarities tot-haplotypes ofMus domesticus
Authors: Forejt Jiří , Gregorová Soňa , Jansa Petr 
Published: September 2009

SummaryThree newt-haplotypes,tp 4,tp 12andtp 14, were isolated fromM. musculusmale mice captured in Central and East Bohemia, Czechoslovakia, about 400 km from the zone of hybridization betweenM. musculusandM. domesticusspecies. Complementation tests have shown that all three newt-haplotypes belong totw 73group. When compared with 5t-haplotypes fromM. domesticusthey displayed the same pattern ofBamHI restriction fragments withH-2class I genes, and they also shared thet-specific 5·2 kbTaqI fragment of the alpha globin pseudogene. However, they differed fromM. domesticus t-haplotypes at the D17Leh443 locus since they all displayed a 10·5 kbMspI fragment, labelled by the Tu443 probe, not found in wild type-chromosomes or inM. domesticus t-haplotypes. A hypothesis is proposed thatt-haplotypes inM. domesticusoriginated by a single successful introgression from a parental species during speciation.
The rate of polygenic mutation
Authors: Lynch Michael 
Published: September 2009

SummaryBy application of the neutral model of phenotypic evolution, quantitative estimates of the rate of input of genetic variance by polygenic mutation can be extracted from divergence experiments as well as from the response of an inbred base population to selection. The analytical methods are illustrated through a survey of data on a diversity of organisms includingDrosophila, Tribolium, mice, and several crop species. The mutational rate of introduction of genetic variance (Vm) scaled by the environmental variance (VE) is shown to vary between populations, species, and characters with a range of approximately 10−4to 5 × 10−2.Vm/VEforDrosophilaviability is somewhat below this range, while hybrid dysgenesis may temporarily inflateVm/VEbeyond 10−1. Potential sources of bias and error in the estimation ofVmare discussed, as are the practical implications of the observed limits toVm/VEfor projecting the long-term response to selection and for testing adaptational hypotheses.
Clustering of rDNA containing type 1 insertion sequence in the distal nucleolus organiser ofDrosophila melanogaster: implications for the evolution of X and Y rDNA arrays
Authors: England P. R. , Stokes H. W. , Frankham R. 
Published: September 2009

SummaryThe ribosomal RNAs produced by the multigene families on theXandYchromosomes ofDrosophila melanogasterare very similar despite the apparent evolutionary isolation of theXandYchromosomal rDNA.X–Yexchange through the rDNA is one mechanism that may promote co-evolution of the two gene clusters by transferringYrDNA copies to theXchromosome. This hypothesis predicts that the proximal rDNA ofXchromosomes will beY-like. Consequently, rDNA variants found only on theXchromosome (such as those interrupted by type 1 insertions) should be significantly clustered in the distalXnucleolus organizer. Proximal and distal portions of theXchromosome nucleolus organizer were separated by recombination between the inverted chromosomesIn(1)scv2(breakpoint in the centre of the rDNA) andIn(1)sc4Lsc8R(no rDNA). Molecular analyses of the resulting stocks demonstrated that rRNA genes containing type 1 insertions were predominantly located on the chromosome carrying the distal portion of theXrDNA, thus confirming a prediction of theX–Yexchange hypothesis for the co-evolution ofXandYchromosomal rDNA. Distal clustering is not predicted by the alternative hypotheses of selection or gene conversion.
Specificities of IncF plasmid conjugation genes
Authors: Willetts Neil , Maule John 
Published: September 2009

SummaryThe conjugation regions of IncF plasmids are closely related in that they share extensive DNA homology, and that they specify related pili. Variations between individual conjugation gene products of different IncF plasmids have, however, been noted. We have extended these observations by carrying out a systematic survey of twelve such plasmids, to examine the numbers and the groupings of the plasmid-specific alleles of several genes required for conjugation and its control.Using vector plasmids carrying cloned origins of transfer (oriT), four different specificities were recognized, and these were correlated with the specificities of the genes with products that may act at this site (traM, traYandtraZ). ThetraYgene is the first gene of the major transfer operon, and is therefore located close to the site at which thetraJprotein acts to induce expression of the operon: correspondingly, correlation was observed between theoriT/traMYZandtraJspecificities in most of the plasmids. In turn,traJis negatively regulated by thefinOandfinPproducts acting in concert: thefinOproduct was relatively non-specific, but sixfinPalleles were identified, again with specificities correlated with those oftraJ. Our explanation for this unexpectedly large number offinPalleles derives from the concept that thefinPproduct is an RNA molecule rather than a protein. Although the conjugative pili encoded by IncF plasmids are closely related, they confer different efficiencies of plating of the various F-specific bacteriophages. We distinguished four groups on this basis, presumably resulting from differences in the primary amino-acid sequences of the pilin proteins. These groups could be related to the surface exclusion system specificities, consistent with the hypothesis that surface exclusion acts at least in part by preventing interaction between the pilus and the recipient cell surface.From these data, information about the evolutionary relationships between the twelve IncF plasmids can be deduced.
Assaying chromosome arrangement in embryonic interphase nuclei ofDrosophila melanogasterby radiation induced interchanges
Authors: Hilliker Arthur J. 
Published: September 2009

SummaryDespite recent advances in our understanding of chromatin ultrastructure, little is known of the arrangement of chromosomes during interphase, the portion of the cell cycle associated with somatic gene transcription. An experimental procedure is described which has allowed the determination of the nature of the relative arrangement during interphase of chromosomes in a specific diploid cell type of Drosophila, the salivary gland anlage of the 10–14-h-old embryo. At this stage of development the salivary gland cells have ceased mitotic divisions. Embryos of 10–14 h in age were irradiated with 12000 rads of gamma radiation and then allowed to develop into third instar larvae. The polytene chromosomes of these larvae were examined for radiation-induced interchanges. From the distribution of observed interchanges, three major features of interphase chromosome arrangement were inferred. (1) Each euchromatic chromosomal arm occupies a specific domain within the interphase nucleus which does not appreciably overlap with those of other arms. (2) Within these chromosomal domains DNA folding is very extensive. (3) The heterochromatic regions of each chromosomal arm are sequestered from the euchromatic regions. An additional point of interest concerns the nature of the interchanges observed. No reciprocal interchanges were observed – all appeared to be partial exchanges, possibly subchromatid interchanges involving only one DNA strand from each of the two exchange sites.
Effects of alleles at the agouti locus on minor skeletal variants in C57BL/6 house mice
Authors: Leamy Larry , Bradley David 
Published: September 2009

SummaryIn this study, five separate alleles at the agouti locus in house mice were tested for potential effects on a battery of 13 minor skeletal variants. Six genotypes (aa,ata,atat,Aa,Avya, andAya) were compared on a standard congenic background (C57BL/6). In log-linear analyses, three of the 13 characters showed significant genotype differences (another three were close to significance), and genotypes also exhibited overall significance in a multivariate randomization test. Both multidimensional scaling and clustering showed an association ofaawithata,AawithAvyaandAya, and a general separation ofatatfrom the other genotypes. Genotype differences averaged 0·63 in probit standard deviations, 0·09 when assessed by the mean measure of divergence. Since the general magnitude of effects of these major genes was quite similar to those previously estimated for presumptive polygenes from subline divergence studies, it was concluded that major genes may often act as polygenes and make important contributions to the variation in minor skeletal variants.
Fitness as a function of β-galactosidase activity inEscherichia coli
Authors: Dean Antony M. , Dykhuizen Daniel E. , Hartl Daniel L. 
Published: September 2009

SummaryChemostat cultures in which the limiting nutrient was lactose have been used to study the relative growth rate ofEscherichia coliin relation to the enzyme activity of β-galactosidase. A novel genetic procedure was employed in order to obtain amino acid substitutions within thelacZ-encoded β-galactosidase that result in differences in enzyme activity too small to be detected by ordinary mutant screens. The cryptic substitutions were obtained as spontaneous revertants of nonsense mutations within thelacZgene, and the enzymes differing from wild type were identified by means of polyacrylamide gel electrophoresis or thermal denaturation studies. The relation between enzyme activity and growth rate of these and other mutants supports a model of intermediary metabolism in which the flux of substrate through a metabolic pathway is represented by a concave function of the activity of any enzyme in the pathway. The consequence is that small differences in enzyme activity from wild type result in even smaller changes in fitness.
Properties of spontaneous mitotic recombination occurring in the presence of therad52-1mutation ofSaccharomyces cerevisiae
Authors: Hoekstra Merl F. , Naughton Tom , Malone Robert E. 
Published: September 2009

SummaryAll major recombination pathways in the yeastSaccharomyces cerevisiaerequire theRAD52gene product. We have examined the effect of therad52-1mutation on spontaneous mitotic recombination between heteroalleles, and found that prototrophs are produced at frequencies significantly above reversion. This residual recombination occurs at a relatively uniform level at all of the loci examined. To help understand the role thatRAD52plays in mitotic recombination, we examined recombination between all pairwise combinations of six mutant alleles of theLYS2gene. Therad52-1mutation decreased the variation in amount of recombination between the various pairwise combinations as well as lowering the overall frequency of recombination. The reduced variation results in a different pattern of recombination inrad52-1cells than in wild type. One interpretation of these results is that theRAD52gene product, directly or indirectly, plays a role in the formation or the resolution of mismatches in heteroduplex DNA.
A sex-linked enzyme in a reptile – association with a recent centric fusion in the common lizard
Authors: Goux Jean-Michel , Pasteur Georges 
Published: September 2009

SummaryIn a series ofLacerta viviparasamples from southern France's central mountains, the distribution of genotypes at the mannose phosphate isomerase (MPI) locus has only been accountable as due to sex linkage in female heterogamety, provided the W chromosome carries only one of the two observed alleles in the populations sampled. This is in perfect accordance with cytogenetical data. Reasons are presented that seem to limit acceptable hypotheses for the recent origin of this sex-linked polymorphism to three: a founder effect, a point mutation in Z chromosomes after crossover suppression, or hitch-hiking with the translocation involved.
Models of long term artificial selection in finite population
Authors: Hill William G. , Rasbash Jonathan 
Published: September 2009

SummaryThe effects of population size and selection intensity, which are in the breeder's control, are investigated for ranges of values of quantities outside his control, namely the number, initial distribution of frequencies and effects of genes influencing the trait. Two alleles are assumed to be initially segregating at each locus, with no linkage, dominance or epistasis. The effects are assumed to follow a gamma distribution, using a wide range of its two parameters which specify both mean gene effect or selective value and the shape of the distribution, or the ratio of Wright's effective number to actual number of genes. The initial gene frequencies (q) are assumed to be either 0·5 at all loci, uniformly distributed over the range 0–1, or to have a U-shaped distribution, proportional to [q(1 −q)]−1such as derives from neutral mutation, with gene effect and frequency distributions independent. The mean and variance of selection response and limits, in the absence of new mutation, are derived.The shape of the distribution of effects is not usually important even up to the selection limit. With appropriate parametrization, the influence of the initial frequency distribution is small over a wide range of parameters. For reasonable choices of parameters, the effects of changing population size from those typically used in animal breeding programmes are likely to be small, but not negligible. For the initial U-shaped frequency distribution, further increases in population size are always expected to give a greater limit, regardless of present value, but not for the other distributions.
Genomic structure of phage F22, a hybrid between serologically and morphologically unrelatedSalmonella typhimuriumbacteriophages P22 andFels 2
Authors: Yamamoto Nobuto , McDonald Robert J. 
Published: September 2009

SummarySalmonella typhimuriumphage P22 can recombine with a serologically and morphologically unrelated Salmonella phageFels 2to yield the hybrid phage F22 at a frequency of about 10−12. F22 has inherited the entire late genes (protein coat and tail structural genes) ofFels 2but carries some P22 early genes. P22 genes in the F22 phage were indentified by marker rescue of various P22 mutants. The F22 genome carries thex-erf-c-18-12segment of the P22 genome. A number of P22 amber mutants were also tested to support these data. The F22 region homologous to P22 was mapped by scoring the ratio of P22 backcross recombinant types in lysates of F22 lysogens superinfected with P22c2ts12. The ratio of the distances between these markers and the ends of the homologous region was determined. Furthermore a new F22 hybrid designated F22dis, containing both P22 immunity regions (candIm), was isolated at a frequency of about 10−4by superinfecting F22 lysogens with P22. F22disphage has lost someFels 2gene(s) which have been replaced by the P22 segment containing theImregion, resulting in formation of a defective hybrid phage.
Effect of thebncAgene on the instability ofAspergillus nidulans
Authors: Pizzirani-Kleiner Aline A. , Azevedo J. L. 
Published: September 2009

SummaryThe presence of a gene designatedbncAwhich produces binucleate and trinucleate conidia inA. nidulansalters the instability of disomics, diploids, and strains with chromosome duplication. In disomics, the genebncAincreases instability. In duplicate and diploid strains, thebncAgene reduces instability by acting as a partial stabilizer. In the strain with chromosome duplication, thebncAgene produces increased percentages of bi- and trinucleate conidia, a fact that may be interpreted to be due to the larger conidial volume of this strain or to the combined effect ofbncAand of the strain, which normally already exhibits a small amount of binucleate conidia.
The site of action of the asebia locus (ab) in the skin of the mouse
Authors: Pennycuik Pamela R. , Raphael Kathryn A. , Chapman R. E. , Hardy Margaret H. 
Published: September 2009

SummaryIn mice homozygous for the asebia mutation (abJ/abJ) the sebaceous glands were small and the sebaceous cells abnormal, the fully grown hair follicles were twice as long as those in wild-type (+ / +) mice, the catagen and telogen follicles were abnormal and, because the active phase of the hair cycle was longer than in + / + mice, the initiation of the second hair cycle was delayed. The abnormalities in the sebaceous glands and in catagen and telogen follicles were also present in abJ/abJ embryonic skin grown on a nude host but anagen of the second hair cycle commenced at about the same time in abJ / abJ and + / + grafts. When recombinants incorporating mutant or wild-type epidermis and dermis were grown on a nude host, the abnormalities in the sebaceous glands and the catagen and telogen follicles were only observed in the recombinants incorporating abJ / abJ epidermis. It was concluded that mutant activity in the epidermis was responsible for the abnormalities in the sebaceous glands and in catagen and telogen follicles and that mutant activity at some site distant from the skin was responsible for the abnormalities in the timing of the hair cycles.
An attempt to estimate the effective size of the ancestral species common to two extant species from which homologous genes are sequenced
Authors: Takahata Naoyuki 
Published: September 2009

SummaryWhen DNA sequence data on various kinds of homologous genes sampled from two related species are available, there is a way to infer the effective size of their ancestral species, which is a simple consequence of gene genealogical considerations. This method, when applied to the common ancestral species of human and rat, human and mouse, human and bovine, or rodents and bovine estimates their effective sizes all to be of the order of 107, supporting the view that these species indeed shared, around 75 million years ago, a common ancestral species from which they are descended. The effective size thus estimated would imply that the ancestral species was abundant enough to have ample opportunity for adaptive radiation. The extent of silent polymorphism in that species might have been very large, possibly comparable to the number of silent substitutions accumulated in a gene after the mammalian divergence. Some causes that may alter these results and require a more elaborated statistical analysis are discussed.
Evidence for a new major gene influencing meat quality in pigs
Authors: Le Roy Pascale , Naveau J. , Elsen J. M. , Sellier P. 
Published: September 2009

SummaryThe present investigation primarily deals with the inheritance of a pigmeat quality trait, the Napole technological yield (RTN), a measure of cooked weight to fresh weight. This trait as well as lean percentage at 100 kg liveweight and fattening length from 20 to 100 kg liveweight were recorded on 3459 offspring from 67 sires and 433 dams, and 3052 offspring from 64 sires and 405 dams in Penshire (P66) and Pen Ar Lan (P77) composite lines respectively. The hypothesis of a major 2-allele locus contributing to RTN was tested by use of a segregation analysis method. Highly significant likelihood ratios (mixed vs. polygenic transmission models) lead us to conclude that a major gene RN− exerting an unfavourable effect on RTN is segregating in both lines. Maximum likelihood estimates of the parameters under the hypothesis of mixed (monogenic + polygenic) inheritance show that the difference between the means of the 2 homozygotes amounts to about 3 phenotypic standard deviations of the trait, whereas the complete dominance of RN− cannot be rejected. The frequency of RN− is about 0·6 in both lines. These results are discussed in connection with the previously reported ‘Hampshire effect’ on pigmeat quality, as the Hampshire breed is a common component of the foundation stock of the 2 composite lines under study.
Prediction of rates of inbreeding in selected populations
Authors: Wray Naomi R. , Thompson Robin 
Published: September 2009

SummaryA method is presented for the prediction of rate of inbreeding for populations with discrete generations. The matrix of Wright's numerator relationships is partitioned into ‘contribution’ matrices which describe the contribution of the Mendelian sampling of genes of ancestors in a given generation to the relationship between individuals in later generations. These contributions stabilize with time and the value to which they stabilize is shown to be related to the asymptotic rate of inbreeding and therefore also the effective population size,whereNis the number of individuals per generation and μrandare the mean and variance of long-term relationships or long-term contributions. These stabilized values are then predicted using a recursive equation via the concept of selective advantage for populations with hierarchical mating structures undergoing mass selection. Account is taken of the change in genetic parameters as a consequence of selection and also the increasing ‘competitiveness’ of contemporaries as selection proceeds. Examples are given and predicted rates of inbreeding are compared to those calculated in simulations. For populations of 20 males and 20, 40, 100 or 200 females the rate of inbreeding was found to increase by as much as 75% over the rate of inbreeding in an unselected population depending on mating ratio, selection intensity and heritability of the selected trait. The prediction presented here estimated the rate of inbreeding usually within 5% of that calculated from simulation.