bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recombination load associated with selection for increased recombination
Authors: Charlesworth B. , Barton N. H. 
Published: September 2009

SummaryExperiments onDrosophilasuggest that genetic recombination may result in lowered fitness of progeny (a ‘recombination load’). This has been interpreted as evidence either for a direct effect of recombination on fitness, or for the maintenance of linkage disequilibria by epistatic selection. Here we show that such a recombination load is to be expected even if selection favours increased genetic recombination. This is because of the fact that, although a modifier may suffer an immediate loss of fitness if it increases recombination, it eventually becomes associated with a higher additive genetic variance in fitness, which allows a faster response to directionselection. This argument applies to mutation-selection balance with synergistic epistasis, directional selection on quantitative traits, and ectopic exchange among transposable elements. Further experiments are needed to determine whether the selection against recombination due to trie immediate load is outweighed by the increased additive variance in fitness produced by recombination.
The calculation of recombination frequencies in crosses of allogamous plant species with applications to linkage mapping
Authors: Ritter E. , Salamini F. 
Published: September 2009

SummaryThe recombination frequency (r) between two loci defined by conventional or molecular markers can be estimated by solving proper Maximum Likelihood equations. These are based on expected and observed marker class frequencies in the progeny of a cross, and are specific for each allelic configuration of the parents(1). In a cross between two diploid parents up to four different alleles, besides a null allele, can be detected at one locus. This defines in each parent, considering a locus A, nine basic allelic configurations based on two allelic marker fragments(Ai/Aj), one single marker allele and a null allele (Ai/AO), or just null alleles (AO/AO). With respect to two loci the consideration of all possible diploid allelic configurations in the parents of a cross allows the detection of 21 different expected marker class distributions producing estimates of r in the progeny. General formulas for calculating the ML equations and the corresponding information functions have been developed for the 21 marker class distributions. Simplified formulas have been also derived and the relative efficiency of the information functions compared. As expected, in the majority of cases, allelic marker configurations give more precise estimates of linkage values than single marker configurations. A method for the construction of linkage maps based on two point estimates, linkage subgroups and allelic bridges is presented. The method is an improvementon an original proposal by Ritteret al.(1990).
Dynamics of gametic disequilibria between loci linked to chromosome inversions: the recombination-redistributing effect of inversions
Authors: Navarro Arcadio , Betrán Esther , Zapata Carlos , Ruiz Alfredo 
Published: September 2009

SummaryThe total gametic disequilibrium between two loci linked to polymorphic inversions can be partitioned into two types of components:withinandbetweenchromosome arrangements. The within components depend on the gametic disequilibrium within each chromosome arrangement. The between components depend on the locus-inversion disequilibria. This partitioning has practical applications and is indispensable for studying the dynamics of these systems because inversions greatly reduce recombination in the heterokaryotypes while allowing free, and sometimes different, recombination in each of the homokaryotypes. We provide equations for the per generation change of the various disequilibria for systems with two and three chromosome arrangements, and the general recursive equations predicting the disequilibria after any number of generations for the case of two arrangements. Simulation studies were carried out using different values of the recombination parameters and all possible initial conditions. The results show a complex convergence to linkage equilibrium in inversion systems. The various disequilibria can have local maxima and minima while approaching equilibrium and, moreover, their dynamics cannot be described, in general, using a single parameter, i.e. an effective recombination rate. We conclude that the effects of inversions on gametic disequilibria must be carefully considered when dealing with disequilibriain inversion systems. The formulae provided in this paper can be used for such purpose.
The effect of recombination on background selection
Authors: Nordborg Magnus , Charlesworth Brian , Charlesworth Deborah 
Published: September 2009

SummaryAn approximate equation is derived, which predicts the effect on variability at a neutral locus of background selection due to a set of partly linked deleterious mutations. Random mating, multiplicative fitnesses, and sufficiently large population size that the selected loci are in mutation/selection equilibrium are assumed. Given these assumptions, the equation is valid for an arbitrary genetic map, and for an arbitrary distribution of selection coefficients across loci. Monte Carlo computer simulations show that the formula performs well for small population sizes under a wide range of conditions, and even seems to apply when there are epistatic fitness interactions among the selected loci. Failure occurred only with very weak selection and tight linkage. The formula is shown to imply that weakly selected mutations are more likely than strongly selected mutations to produce regional patterning of variability along a chromosome in response to local variation in recombination rates. Loci at the extreme tip of a chromosome experience a smaller effect of background selection than loci closer to the centre. It is shown that background selection can produce a considerable overall reduction in variation in organisms with small numbers of chromosomes and short maps, such asDrosophila. Large overall effects are less likely in species with higher levels of genetic recombination, such as mammals, although local reductions in regions of reduced recombination might be detectable.
Estimating variance effect of QTL: an important prospect to increase the resolution power of interval mapping
Authors: Korol A. B. , Ronin Y. I. , Tadmor Y. , Bar-Zur A. , Kirzhner V. M. , Nevo E. 
Published: September 2009

SummaryEqual variances within quantitative trait locus (QTL) groups in the segregating population are a usual simplifying assumption in QTL mapping. The objective of this paper is to demonstrate the advantages of taking into account potential variance effect of QTLs within the framework of standard interval mapping approach. Using backcross case as an example, we show that the resolution power of the analysis may be increased in the presence of variance effect, if the latter is allowed for in the model. For a putative QTL (say,A/a) one can compare two situations, (i)and (ii). It was found that, if the variance effect ofA/ais large enough, then in spite of the necessity to evaluate an increased number of parameters, the more correctly specified model provides an increase in the resolution power, as compared to the situation (i). This is not unexpected, if eitherin (ii) is lower thanfrom (i). But our conclusion holds even if. These advantages are illustrated on sweet corn data data (F3families of F2genotypes). In particular, the log-likelihood test statistics and the parameter estimates obtained for a QT locus in the distal region of chromosome 2 show that the allele enhancing the trait is recessive over the opposite allele simultaneously for the mean value and variance.
Genetic control of male cuticular hydrocarbons inDrosophila melanogaster
Authors: Ferveur Jean-François , Jallon Jean-Marc 
Published: September 2009

Summary7-tricosene (7-T) and 7-pentacosene (7-P) are the two main hydrocarbons on the cuticle of maleDrosophila melanogaster. These two substances might play a pheromonal role during courtship behaviour. We investigated the genetic basis of the quantitative polymorphism observed in the production of 7-T and 7-P. Strains of different geographic origin, with males producing either predominantly 7-T or predominantly 7-P, were hybridized with strains carrying genetic markers. We found that chromosome II changes the balance between 7-T and 7-P while chromosome III regulates the overall quantity of both 7-monoenes. We have also characterized and roughly mappedseptandsmoq, two genetic factors on chromosome II that act additively on the production of both cuticular hydrocarbons. The genetic control of the variation in 7-T and 7-P varies betweenD. melanogasterstrains and betweenD. melanogasterand its sibling speciesD.simulans. The possible evolutionary and physiological causes of this variation as well as its functional implication for courtship behaviour are discussed.
Lack of correlation between dysgenic traits in thehobosystem of hybrid dysgenesis inDrosophila melanogaster
Authors: Bazin C. , Higuet D. 
Published: September 2009

SummaryCurrently in thehobosystem of hybrid dysgenesis, strain classification is based on the presence/absence of the 2·6 kbXhoI restriction fragment. Using this criterion, strains are classified as: (1) H strains when full-size elements are detected by presence of a 2·6 kbXhoI restriction fragment; they can also contain internally deleted elements; (2) DH strains when only deleted elements are detected (XhoI restriction fragment less than 2·6 kb); (3) E strains, devoid of any restriction fragment equal to or less than 2·6 kb in length. In addition, the strains can be classified on their ability to generate gonadal atrophy (GD sterility) when males of a studied strain are crossed with females from an E strain (dysgenic cross). Here we try to define the nature of the dysgenic cross, which leads us to analyse the different components of the dysgenic syndrome and to look for eventual correlations between them. Molecular analysis, GD sterility tests, hobo mobilization with the haw strain and thevgalstrain, and hereditary transmission of the instability at thevglocus have been assayed in different strains. We show that the occurrence of GD sterility depends on the tested H strains as expected, but also on the E strains used. On the other hand we do not find any correlation between the different dysgenic parameters. Our data reveal that molecular and GD sterility tests are not sufficient to classify strains in thehobosystem, and that all the components of the dysgenic syndrome must be taken into account. Our results are discussed with regard to active and full-size elements in relation to the structure of the S region where an amino acid sequence (TPE) presents a repetition polymorphism
Evolution of multiple families of non-LTR retrotransposons in phlebotomine sandflies
Authors: Booth David R. , Ready Paul D. , Smith Deborah F. 
Published: September 2009

SummaryIn this paper we report on the diversity and distribution of a set of non-LTR retrotransposon (RTP) reverse transcriptase (RT) sequences isolated from phlebotomine sandflies, and their potential for investigating the evolutionary histories of members of this subfamily of flies (Diptera: Psychodidae, Phlebotominae). The phlebotomine RT sequence families derived from one species were as different from each other as they were from RT sequences derived from other species. When each was used to probe Southern blots of sandfly genomic DNA they hybridized only to the species of source and, usually, to others of the same subgenus, but not to DNA from other subgenera — a hybridization pattern consistent with vertical evolution. There was considerable intraspecific variation in hybridization pattern, suggesting the RTs were part of non-LTR RTPs that are (or were recently) subject to flux in genomic position and copy number. Most of the RT families detected in phlebotomines are monophyletic with respect to previously described RTs, and all are monophyletic with RTs of the F/Jockey (Drosophila melanogaster) type of RTP. Orthologous sequences were isolated from the closely related species Phlebotomus perniciosus and P. tobbi (subgenus Larroussius), and different populations of P. perniciosus. The level of sequence divergence among these orthologous RTs, the subgeneric distribution of each RT family, and the intraspecific variation in hybridization pattern of many of them, indicate this class of sequence will provide genetic markers at the sub-generic level.
An additional type of male sterility and inherited urinary obstruction in mice with thet-haplotypeth7
Authors: Lyon Mary F. 
Published: September 2009

SummaryThet-complex on mouse chromosome 17 results in transmission ratio distortion in males heterozygous for complete haplotypes, and sterility in those homozygous for semi-lethal or doubly heterozygous for complementing lethal haplotypes. This sterility is due to inability of spermatozoa to fertilize. The haplotypeth7is an unusual laboratory-derived haplotype, postulated to carry a small duplication oftchromatin. Males heterozygous forth7show a new form of sterility, apparently due to failure to form copulation plugs during mating. This is accompanied by a strong propensity to acute urinary obstruction. It is suggested that both the failure to form copulation plugs and the urinary obstruction are due to some abnormality in function of the accessory sex glands, and are the result of incorrect dosage of a gene in the postulated duplication. The symbolMsufor male sterility and urinary obstruction is suggested for the locus concerned. Previously a recessive form of abnormal behaviour had also been attributed to this duplication.
Morphology and behaviour of silver-stained chromatid cores in mitotic chromosomes analysed by whole mount electron microscopy
Authors: Zhao Jian , Jin Shaobo , Hao Shui , Chen Ruiyang 
Published: September 2009

SummaryUsing silver staining and the whole mount electron microscopy technique of squashed chromosomes, we studied the substructural organization and behaviour of chromatid cores in mitotic chromosomes of spermatogonia of the grasshopper Oedaleus infernalis during mitosis. It was found that the formation of mitotic chromatid cores takes place during the transition from prophase to prometaphase. Each chromosome contains two compact chromatid cores which are surrounded by a halo of dispersed argyrophilic material emanating radially from the cores. In early metaphase the chromatid core usually appears as an extended, slender network running longitudinally through the entire length of the chromatid, while in late metaphase the core frequently has a spiral appearance. In addition, our results revealed the existence of interconnections between sister chromatid cores along their entire length, as a result of which sister chromatid cores appear as a single interconnected core network in mitotic metaphase chromosomes. At this stage the core occupies a lateral position in each chromatid. However, during the transition from metaphase to anaphase, the interconnections are gradually released to allow the individualization of sister chromatid cores and the segregation of chromosomes. The core comes to occupy a central position in each segregated chromatid. These findings demonstrate the presence of an intrinsic interconnected core network within metaphase chromosomes which could be involved in the maintenance and segregation of chromosomes during mitosis.
Time of initiation and site of action of the mouse chromosome 11 imprinting effects
Authors: Cattanach Bruce M. , Beechey Colin V. , Rasberry Carol , Jones Janet , Papworth David 
Published: September 2009

SummaryPrevious studies have shown that mice with paternal disomy for chromosome 11 are consistently larger at birth than their normal sibs, whereas mice with the maternal disomy are consistently smaller. An imprinting effect with monoallelic expression of some gene/s affecting growth was indicated. Here we show that the size differences become established prior to birth and are only maintained subsequently, indicating that the gene repression is limited to prenatal development. Fetal analysis was limited to 12·5–17·5 days post coitum. However by extrapolating the data backwards it could be calculated that both the maternal and paternal size effects might commence as early as 7 days post coitum, although possibly slightly later. It may be deduced that initiation of expression of the gene/s responsible may occur at about this time in development. The two disomy growth rates were mirror-images of each other, suggesting that expressed gene dosage is the underlying cause. Differential growth of the placentas of the two disomies was also found, and extrapolation of these data backwards suggested that the placental size differences were initiated later in development than those for the fetuses. The differential placental growth of the maternal and paternal disomies may therefore have developed independently or emerged as a consequence of the differential fetal growth. In either event it would seem that the expression of the responsible gene occurs in the fetus itself to cause the anomalies of growth. The data therefore provide information on the temporal and tissue specificity of the gene/s responsible for the chromosome 11 imprinting effects. Possible candidate genes are discussed.
Population structure of a riparian willow species,Salix viminalisL.
Authors: Lascoux Martin , Thorsén Johanna , Gullberg Urban 
Published: September 2009

SummaryMaterial sampled along 11 rivers of the western part ofSalix viminalisL. natural range (in Poland, Germany and Austria), as well as in stands in Sweden and Belgium, was assayed for 15 isozyme loci and cuttings were installed in two field experiments located in a nursery south of Uppsala, where growth traits were measured. These data were used to test hypotheses on the origin of Swedish populations, on the part played by rivers in the genetic differentiation and on the relative differentiation at isozyme and quantitative trait loci. Although significant, the overall population differentiation was low, theFSTvalue being around 4%. Much higherFSTvalues were observed between subpopulations from southern (Skåne) and central Sweden. This strong population differentiation, accompanied by significant linkage disequilibria, suggests the recent and diverse origin of Swedish populations. Degrees of differentiation between and within Polish river systems were of the same magnitude, indicating the presence of gene flow between river systems. Flow-regulated waterways, associated with higher human disturbance, may well explain why populations along rivers of the western part of the study area exhibited significant differentiation patterns while no differentiation could be detected along the less disturbed riparian habitats of eastern Poland. Finally, higherFSTvalues were obtained for quantitative trait loci than for isozyme loci but, with two notable exceptions, their 95 % confidence intervals overlapped.
Mother-offspring data in a study of the mating system in a natural population of Bulinus globosus (Gastropoda: Planorbidae) in Zimbabwe
Authors: Mukaratirwa S. , Chandiwana S. K. , Siegismund H. R. , Kristensen T. K. 
Published: September 2009

SummaryThe mating system of a natural population of Bulinus globosus from the Chiweshe area, Zimbabwe, was studied with mother—offspring data using isozyme genetic markers. The study was done in response to work on the genetic structure of this population which suggested a limited extent of cross-fertilization. Of the 24 adults whose progenies were analysed, at least 15 showed evidence of outcrossing and 9 had results consistent with selfing. These results show that the two modes of reproduction are important under natural conditions and the mating system of this population is considered to be ‘partially-selfing’.
Reduced variation atconcertina, a heterochromatic locus inDrosophila
Authors: Wayne Marta L. , Kreitman Martin 
Published: September 2009

SummaryInDrosophila melanogasterand closely related species, polymorphism has been shown to be reduced at loci located in regions of low recombination on the X chromosome and on the fourth chromosome, which does not normally recombine. Thispositive correlation between nucleotide polymorphism level and recombination rate is not predicted by standard neutral theory and therefore must result from natural selection and genetic hitchhiking along the chromosomes. We report here the near-complete absence of variation atconcertina(cta), a locus located in the β-heterochromatic base ofchromosome 2L, a region of strongly reduced recombination. A 1.2 kilobase region containing coding regions and introns was sequenced from each of nine lines ofD. melanogasterand nine lines ofD. simulansrepresentingworldwide collections. Variation is significantly reduced inctain both species compared with other available loci on the same chromosome. Two analyses of background selection demonstrate that the reduction in variation atcta, considered in combination with other loci on chromosome 2L or alone, is consistent with the background selection model.
The negative correlation between somatic aneuploidy and growth in the oysterCrassostrea gigasand implications for the effects of induced polyploidization
Authors: Zouros E. , Thiriot-Quievreux C. , Kotoulas G. 
Published: September 2009

SummaryThis study extends previous observations that chromosome loss in somaticcells of juveniles of the pacific oysterCrassostrea gigasis associated with reduced growth rate. All four studies designed to examine this association (two usingrandom population samples and two using full sibs) produced the same result. This consistent effect appears to be unrelated with the commonly, but not consistently, observed correlation between degree of allozyme heterozygosity and growth. We propose thatthe inverse relationship between aneuploidy and growth is due to the unmasking of deleterious recessive genes caused by ‘progressive haploidization’ of somatic cells. Because unmasking of deleterious recessive genes by random chromosome lossisunlikely in polyploid cells, this hypothesis may also provide an explanation for theobservation that artificially produced polyploid shellfish usually grow at faster rates than normal diploid ones.
Genetics of a difference in cuticular hydrocarbons betweenDrosophila pseudoobscuraandD. persimilis
Authors: Noor Mohamed A. F. , Coyne Jerry A. 
Published: September 2009

SummaryWe identify a fixed species difference in the relative concentrations of the cuticular hydrocarbons 2-methyl hexacosane and 5,9-pentacosadiene inDrosophilapseudoobscuraandD. persimilis, and determine its genetic basis. In backcross males, this difference is due to genes on both the X and second chromosomes, while the other two major chromosomes have no effect. In backcross females, only the second chromosome has a significant effect on hydrocarbon phenotype, but dominant genes on the X chromosome could also be involved. These results differ in two respects from previous studies ofDrosophilacuticular hydrocarbons: strong epistasis is observed between the chromosomes that producethe hydrocarbon difference in males, and the difference is apparently unrelated to the strong sexual isolation observed between these species.