bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thirteen genes (Cebpb, E2f1, Tcf4, Cyp24, Pck1, Acra4, Edn3, Kcnb1, Mc3r, Ntsr, Cd40, Plcg1andRcad) that probably lie in the distal imprinting region of mouse Chromosome 2 are not monoallelically expressed
Authors: Williamson Christine M. , Dutton Elizabeth R. , Abbott Catherine M. , Beechey Colin V. , Ball Simon T. , Peters Josephine 
Published: September 2009

SummarySeven imprinted genes are currently known in the mouse but none have been identified yet in the distal imprinting region of mouse Chromosome (Chr) 2, a region which shows striking linkage conservation with human chromosome 20q13. Both maternal duplication/paternal deficiency and its reciprocal for distal Chr 2 lead to mice with abnormal body shapes and behavioural abnormalities. We have tested a number of candidate genes, that are either likely or known to lie within the distal imprinting region, for monoallelic expression. These included 3 genes (Cebpb,E2f1andTcf4) that express transcription factors, 2 genes (Cyp24andPck1) that are involved in growth, 5 genes (Acra4,Edn3,Kcnb1,Mc3randNtsr) where a defect could lead to neurological and probably behavioural problems, and 3 genes (Cd40,Plcg1andRcad) that are less obvious candidates but sequence information was available for designing primers to test their expression. On/off expression of each gene was tested by reverse transcription–polymerase chain reaction (RT–PCR) analysis of RNA extracted from tissues of mice with maternal duplication/paternal deficiency and its reciprocal for the distal region of Chr 2. None of the 13 genes is monoallelically expressed in the appropriate tissues before and shortly after birth which suggests that these genes are not imprinted later in development. This study has narrowed down the search for imprinted genes, and valuable information on which genes have been tested for on/off expression is provided. Since there is considerable evidence of conservation of imprinting between mouse and human, we would predict that the 13 genes are not imprinted in human. Five of the genes:E2f1,Tcf4,Kcnb1,Cd40andRcad, have not yet been mapped in human. However, because of the striking linkage conservation observed between mouse Chr 2 and human chromosome 20, we would expect these genes to map on human chromosome 20q13.
Accumulation of mutations affecting body weight in inbred mouse lines
Authors: Caballero Armando , Keightley Peter D. , Hill William G. 
Published: September 2009

SummaryThe variation from spontaneous mutations for 6-week body weight in the mouse was estimated by selection from a cross of two inbred sublines, C57BL/6 and C57BL/10, separated about 50 years previously from the same inbred line. Selection was practised high and low for 12 generations from theF2, followed by one generation of relaxation. The lines diverged by approximately 1·7 g or 0·7 sd. The additive genetic variance was estimated in theF2by restricted maximum likelihood and from the selection response, and from this variance the mutational heritabilityhM2was estimated using the number of generations since divergence. Estimates ofhM2range from 0·08 to 0·10% depending on the method of analysis. These estimates are similar to those found for other species, but lower than other estimates for the mouse. It is concluded that substantial natural and, perhaps, artificial selection operated during the maintenance of the sublines.
Survey of genomic repeat sequence-PCRs that detect differences between inbred mouse strains
Authors: Wood Philip A. , Hamm Doug A. 
Published: September 2009

SummaryWe have developed molecular markers that distinguish between several inbred and congenic mouse strains using polymerase chain reaction (PCR) amplification of genomic DNA repeat sequences. Mouse genomic DNA, digested with four base recognition site-restriction endonucleases, was amplified by PCR using primers for the following repeat sequences: Bl (Alu homolog), LINE, LLR3, IAP, human Alu and myoglobin. Amplification products analysed by agarose gel electrophoresis and stained with ethidium bromide produced unique DNA fragments, some of which are specific for each of 12 strains tested. This method can be used for molecular analysis of the mouse genome, including genetic monitoring.
Preserving genes: a model of the maintenance of genetic variation in a metapopulation under frequency-dependent selection
Authors: Judson Olivia P. 
Published: September 2009

SummaryUnderstanding how genetic variability is maintained in natural populations is of both theoretical and practical interest. In particular, the subdivision of populations into demes linked by low levels of migration has been suggested to play an important role. But the maintenance of genetic variation in populations is also often linked to the maintenance of sexual reproduction: any force that acts to maintain sex should also act to maintain variation. One theory for the maintenance of sex, the Red Queen, states that sex and variation are maintained by antagonistic coevolutionary interactions – especially those between hosts and their harmful parasites – that give rise to negative frequency-dependent selection. In this paper I present a model to examine the relationships between population subdivision, negative frequency-dependent selection due to parasites, the maintenance of sex, and the preservation of alleles from fixation. The results show strong interactions between migration rates, negative frequency-dependent selection, and the maintenance of variability for sexual and asexual populations.
A stochastic model of selection on selfing rates in structured populations
Authors: Ronfort J. , Couvet D. 
Published: September 2009

SummaryPrevious theoretical studies of the evolution of the selfing rate have shown that mixed mating systems are not evolutionary stable states. Such models have, however, not included the effects of population structure and thus biparental inbreeding together with the evolution of selfing rates and inbreeding depression. In order to examine selection on selfing rates in structured populations, a stochastic model simulating a finite population with partial selfing and restricted pollen and seed dispersal has been developed. Selection on the mating system was followed by introducing modifiers affecting the selfing rate. The major result was that, with density dependent recruitment, a process which maintains the population structure necessary for biparental inbreeding to occur, a mixed mating system could be maintained. This result was associated with an increase of the mutation load with high selfing rates, and the selected selfing rate depended on the degree of population structure rather than on the initial selfing rate. With low dominance of deleterious alleles, complete allogamy can be selected for. Further studies showed that the more general condition of spatial heterogeneity of recruitment can lead to similar results, the most important condition being the maintenance of genetic structure within populations. A brief survey of the empirical literature shows that a positive relationship between the magnitude of inbreeding depression and the inbreeding coefficient within populations has been observed, in support of the present model.
Esterase polymorphism in insecticide susceptible populations of the mosquitoCulex pipiens
Authors: Raymond Michel , Qiao Chuan L. , Callaghan Amanda 
Published: September 2009

SummaryGene amplification involving a particular haplotype has been found at the esterase B locus of mosquitoes from various countries. This similarity has been explained by a unique amplification event followed by migration and selection by organophosphate (OP) insecticides. This assumes that the polymorphism of non-amplified esterase haplotypes is so large that the chance of independent amplification in two distinct populations is negligible. In order to test this assumption, three susceptible populations from northern Europe were sampled and analysed for esterase and haplotype polymorphism. At the protein level, 18 and 16 alleles were found for esterase A and B respectively in one French population (n= 74), and 16 and 14 in an English one(n= 50). At the DNA level, 24 alleles at the esterase B locus were detected in a sample of 72 mosquitoes from one population, with the use of only one restrictionenzyme (EcoR V). Restriction maps of two nonamplified haplotypes randomly sampled from a single breeding site in Belgium were built with six restriction enzymes. 60% of all restriction sites were different among the two maps. The huge polymorphism found in northern Europe requires specific explanations for its stability, but it considerably strengthens the hypothesis of migration of amplified haplotypes.
Interactions of selection, linkage and drift in the dynamics of polygenic characters
Authors: Hospital Frédéric , Chevalet Claude 
Published: September 2009

SummaryWe study the dynamics under directional truncation selection of the genetic variability of a quantitative character controlled by a finite number of possibly linked loci with additive effects. After the first generation of selection, the build-up of linkage disequilibria (Bulmer effect) is analytically demonstrated from a genetical point of view in an infinite population. In the following generations, the dynamics of the system in a finite population are predicted using analytic recurrences under a multi-normal approximation, and computer simulations. The effects of recombination on the dynamics of linkage disequilibria induced by selection and drift, and the consequences for the additive genetic variance are then analysed and discussed from the simulation results. Compared to the rapid exploitation of genetic variability promoted by high recombination rates, low recombination rates promote an early storage of genetic variability in repulsion associations of alleles and a possible late release of genetic variance in the population, so that the variability of the character may be maintained over a longer period of time. In some cases, favourable recombination events in tightly linked systems induce an increase of the additive variance of the character, which may explain some results observed in long-term selection experiments. Our results emphasize that the joint effects of selection, linkage and drift must notbe neglected in theoretical quantitative genetics, and require further investigation.
Identification of the α-galactosidaseMELgenes in some populations ofSaccharomyces cerevisiae: a new geneMEL11
Authors: Naumov Gennadi I. , Naumova Elena S. , Turakainen Hilkka , Korhola Matti 
Published: September 2009

SummaryIn this report we mapped a newMEL11gene and summarize our population studies of the α-galactosidaseMELgenes ofS. cerevisiae. The unique family of structuralMELgenes has undergone rapid translocations to the telomeres of most chromosomes in some specificSaccharomyces cerevisiaepopulations inhabiting olive oil processing waste (alpechin) and animal intestines. A comparative study ofMELgenes in wine, pathogenic and alpechin populations ofS.cerevisiaewas conducted using genetic hybridization analysis, molecular karyotypingand Southern hybridization with theMEL1probe. Five polymeric genes for the fermentation of melibiose,MEL3, MEL4, MEL6, MEL7, MEL11, were identified in an alpechin strain CBS 3081. The newMEL11gene was mapped by tetrad analysis to the left telomeric region of chromosome I. In contrast, in wine and pathogenic populations ofS. cerevisiae, MELgenes have been apparently eliminated. Their rare Mel+strains carry only one of theMEL1, MEL2, orMEL8genes. One clinical strain YJM273 was heterozygotic on theMEL1gene; itsmell0allele did not have a sequence of the gene.
Genomic incompatibilities in the hybrid zone between house mice in Denmark: evidence from steep and non-coincident chromosomal clines for Robertsonian fusions
Authors: Fel-Clair Fabienne , Lenormand Thomas , Catalan Josette , Grobert Jacqueline , Orth Annie , Boursot Pierre , Viroux Marie-Cecile , Britton-Davidian Janice 
Published: September 2009

SummaryThe pattern of chromosomal variation is investigated in house mice from the Danish hybrid zone between the translocation-proneMus musculus domesticusand the chromosomally conservativeM. m. musculus. The cytogenetic analysis confirmed the non-introgression of three pairs of Robertsonian (Rb) fusions fromM. m. domesticusinto theM. m. musculusgenome. The geographic distribution of two of these Rb fusions was shown to follow staggered chromosomal clines which increased in steepness the closer they were to the centre of the hybrid zone as defined by allozymes. Analysis of alternate hypotheses suggests that chromosomal differentiation of the Danishdomesticusoccurred after contact was established withmusculus. The staggering of the clines would reflect the order of arrival of theRb fusions into the hybrid zone. Several models with different processes of underdominance of the chromosomal heterozygotes are discussed to account for the difference in width between clines. A selective model with increasing levels of genomic underdominance due to interaction with a progressively enrichedmusculusgenome provides the best fit for the observed pattern. Selection against Rb fusions with little effect on the recombination of linked allozyme markers supportsthe view that no reduction in gene flow due to chromosomal heterozygosity is yet apparent through the hybrid zone and that only the centromeric segments of the Rb fusions are incompatible with themusculusgenome.
Estimating gene flow in island populations
Authors: Rannala Bruce , Hartigan J. A. 
Published: September 2009

SummaryA new method is presented for estimating the rate of gene flow into island populations using the distribution of alleles in samples from a number of islands. The pseudo maximum likelihood estimator (PMLE) that we derive may be applied to species with either discrete or continuous generation times. For Wright's discrete-generation island model, the method provides an estimate of θ = 2NmwhereNis the (haploid) population size on each island andmis the fraction of individuals replaced by immigrants in each generation. For a continuous-generation island model, the corresponding parameter φ is the ratio of the immigration rate φ to the individual birth rate λ. Monte Carlo simulations are used to compare the statistical properties of the PMLE with those of two alternative estimatorsof θ derived from Wright'sF-statistics. The PMLE is shown to have greatest efficiency (least mean square error) in most cases for a wide range of sample sizes and parameter values. The PMLE is applied to estimate θ using mtDNA haplotypes and allozymes for subdivided populations of African elephants and Channel Island foxes.
Models of the spread of non-autonomous selfish transposable elements when transposition and fitness are coupled
Authors: Brookfield J. F. Y. 
Published: September 2009

SummaryI investigate models of the spread of transposable elements, such as theDrosophila melanogasterP elements, that can exist in autonomous and non-autonomous forms. Elements which have their major impact on host fitness in the process of transposition can, under certain conditions, come to a stable balance between transposition and selection. This stable balance for autonomous elements can be disrupted by the invasion of further elements, which do not produce a transposase enzyme, and may produce a repressor of transposition. I examine this secondary invasion process, and show that a stable equilibrium copy number for intact elements is neither a necessary nor a sufficient condition for non-autonomous elements to invade. Nevertheless, invasion occurs under a broad range of models and conditions. This requires neither that the non-autonomous elements produce atrans-acting repressor of transposition, nor that they titrate transposase. The elimination of autonomous elements follows the increase in non-autonomous elements unless the latter encode powerful repressors of transposition. Approximate solutions for the equilibrium copy number of autonomous elements and rate of invasion of non-autonomous elements can be found under some models for transposition and selection. The predictions of the model are compared with recent empirical studies of theD. melanogasterP system
A study of meiotic pairing, nondisjunction and germ cell death in laboratory mice carrying Robertsonian translocations
Authors: Everett C. A. , Searle J. B. , Wallace B. M. N. 
Published: September 2009

SummaryFrequencies of anaphase I nondisjunction, germ cell death and pairing abnormalities at pachytene were assessed in male mice singly heterozygous and homozygous for the Robertsonian (Rb) translocations: Rb (1.3)lBnr, Rb(ll. 13)4Bnr and Rb(10. ll)8Bnr. Rb homozygotes showed low frequencies of nondisjunction but substantial germ cell death. This germ cell death could not be attributed to problems at pachytene as Rb homozygotes showed no increase in pairing abnormalities over the (C3H/HeH×1O1/H)F1 controls. Instead genie factors are involved. Rb heterozygotes showed substantial frequencies of nondisjunction and even greater germ cell death than found in the homozygotes. Pachytene pairing abnormalities were observed and it appears that these, together with genie factors, cause physiological perturbation of meiocytes, thereby promoting germ cell death, with nondisjunction of the trivalent as a sublethal response.
Interaction of selection and recombination in the fixation of negative-epistatic genes
Authors: Michalakis Yannis , Slatkin Montgomery 
Published: September 2009

SummaryWe investigated the interaction of recombination and selection on the process of fixation of two linked loci with epistatic interactions in fitness. We consider both the probability of fixation of newly arising mutants (the static model) and the time to fixation under continued mutation (the dynamic model). Our results show that the fixation of a new advantageous combination is facilitated by higher fitness of the advantageous genotype and by weaker selection against the intermediate deleterious genotypes. Fixation occurs more rapidly when the recombination rates are small, except when selection against intermediate genotypes is weak and selection in favour of the double mutant is very strong. In these cases fixation is more rapid when the recombinant rate is large. Mutations of strong effects, deleterious when alone but beneficial when coupled, are fixed more easily than mutations of intermediate effects, at least for large recombination rates. Among the possible pathways the process of fixation might follow, independent substitutions lead to the fixation of the double mutant only when selection is weak. The relative importance of the other pathways depends on the interaction between recombination and selection. The coupled-gamete pathway (i.e. when the population waits until the double mutant appears and then drives it to fixation) is more important as selection intensity increases and the recombination rate is reduced. For all recombination rates, asymmetries in fitness of the intermediate genotypes increase the rate at which fixations occur. Finally, throughout the fixation process, the population will be monomorphic at least at one of the two loci for most of the time, which implies that there would be little opportunity to detect the presence of negative epistasis even if it were important for occasional evolutionary transitions.
Waiting for a compensatory mutation: phase zero of the shifting-balance process
Authors: Phillips Patrick C. 
Published: September 2009

SummaryIn highly integrated genetic systems, changes in any one component may have a deleterious effect on fitness, but coordinated, or compensatory, change in these components could lead to an overall increase in fitness compared with the current state. Wright designed his shifting-balance theory to account for evolutionary change in such systems, since natural selection alone can not lead to the new optimal state. A largely untreated aspect of the shifting-balance theory, that of the limiting impact of waiting for the production of new mutations, is analysed here. It is shown that the average time to double fixation of compensatory mutations is extremely long (of the order of tens or hundreds of thousands of generations), because selection is too effective in large populations, and mutations are too rare in small populations. Further, the probability that a new mutant will arise and undergo fixation quickly is extremely small. Tight linkage can reduce the time to fixation somewhat, but only in models in which the double heterozygote does not have reduced fitness. It is argued that the only reasonable way for compensatory mutations to become fixed in a population is if the new mutants are first allowed to achieve a moderate frequency through the relaxation of selection. Under these conditions, the time required to reach fixation is reasonably low, althoug the probability of being fixed is still small when the initial allele frequencies are low. It is likely that the waiting time for fixation of new mutants, which is here called phase zero, is the major limiting factor for the success of the shifting-balance process
Microsatellite polymorphisms in a wild population of Drosophila melanogaster
Authors: England Phillip R. , Briscoe David A. , Frankham Richard 
Published: September 2009

SummaryHighly variable DNA polymorphisms called microsatellites are rapidly becoming the marker of choice in population genetic studies. Until now, microsatellites have not been utilized for Drosophila studies. We have identified eight polymorphic microsatellite loci in Drosophila melanogaster and used them to characterize the genetic variation in a wild population from the Tyrrell's winery in Australia. Microsatellites were isolated from a partial genomic DNA library. All microsatellites consist of (AC)n repeats ranging from n = 2 to n = 24. Six loci were assigned to chromosomal location by genetic mapping, with three loci on chromosome II, one locus on chromosome III and two loci on the X chromosome. Up to four microsatellite loci were multiplexed in the same reaction. Microsatellite variation is substantially greater than allozyme variation in the Tyrrell's Drosophila population. 80% of the microsatellite loci examined are polymorphic, compared with 28% of allozymes. The mean number of alleles per polymorphic locus is 5·2 in microsatellites compared with 30 in allozymes. The average observed heterozygosity of polymorphic microsatellites is 47% compared with 26% for allozymes. Microsatellite variation in Drosophila melanogaster is similar to that reported for other insects. Higher variability commends microsatellites over allozymes for genetic studies in Drosophila melanogaster.
Selection against transposable elements inD. simulansandD. melanogaster
Authors: Vieira C. , Biémont C. 
Published: September 2009

SummaryThe insertion site numbers of the transposable elements (TEs) copia, mdgl, 412 and gypsy were determined in various natural populations ofDrosophila melanogasterandD. simulansby in situ hybridization. We showed that, while all elements except gypsy had many insertion sites scattered over the chromosomes inD. melanogaster, only the 412 element inD. simulanspresented a high number of insertions, and this number was lower than inD. melanogaster. This low 412 site number per genome inD. simulanswas associated with a lower proportion of insertions on the X chromosome in comparison withD. melanogaster, as determined in diploid genomes (0·090 forD. simulansagainst 0·137 forD. melanogaster) and in haploid genomes (0·102 against 0·146), each value being, moreover, lower than the value of 0·20 expected on the hypothesis of no selection against insertional mutations. These results suggest that selection is a major mechanism explaining 412 copy number regulation inDrosophila, and is stronger inD. simulansthan inD. melanogaster.