bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mapping QTLs for binary traits in backcross and F2populations
Authors: Visscher P. M. , Haley C. S. , Knott S. A. 
Published: September 2009

SummaryMapping quantitative trait loci (QTLs) for binary traits in backcross andF2populations was investigated using stochastic stimulation. Data were analysed using either linear regression or a generalized linear model. Parameters which were varied in the simulations were the population size (200 and 500), heritability in the backcross orF2population (0·01, 0·05, 0·10), marker spacing (10 and 20 cM) and the incidence of the trait (0·50, 0·25, 0·10). The methods gave very similar results in terms of estimates of the QTL location and QTL effects and power of QTL detection, and it was concluded that in practice treating the zero-one data as continuous and using standard linear regression was efficient.
High genetic variability under the balance between symmetric mutation and fluctuating stabilizing selection
Authors: Kondrashov Alexey S. , Yampolsky Lev Yu. 
Published: September 2009

SummaryWe have studied variability maintained in a quantitative trait by the balance between symmetric mutation and direct stabilizing selection with a fluctuating optimum. Using a simulational computer model, we have found that wide fluctuations, such that the range of the optimum changes exceeds the width of the fitness curve, increase the trait variance, often by two or three orders of magnitude, over its value under constant selection. This happens because such fluctuations cause frequent allele substitutions at the loci that control the trait. At any particular moment the variance is increased mostly due to one or several loci where more than one allele is currently common. The data on fluctuating selection in nature are reviewed
Insertion of the retroposable element,jockey, near theAdhgene ofDrosophila melanogasteris associated with altered gene expression
Authors: White Lisa D. , Jacobson James W. 
Published: September 2009

SummaryThealcohol dehydrogenase(Adh) gene ofDrosophila melanogasteris well suited to be a gene expression reporter system.Adhproduces a measurable phenotype at both the enzyme and mRNA levels. We recovered a spontaneous transposable element (TE) insertion mutation near theAdhgene. The insertion is a truncated retroposable element,jockey, inserted upstream of the adultAdhenhancer region. Comparisons between theAdhjockeyallele and its direct wild-type ancestral allele were made in an isogenic background (i.e. identicalcisandtransfactors). Differences inAdhjockeyexpression compared with the wild-type can be attributed solely to the presence of thejockeyelement. Thisjockeyinsertion results in a decrease in adult mRNA transcript levels in theAdhjockeyhomozygous lines relative to the wild-type counterpart and accounts for a correlated decrease in alcohol dehydrogenase (ADH) enzyme activity. The larval ADH activity levels are not detectably different.
Genetics of sexual isolation in male hybrids ofDrosophila simulansandD. mauritiana
Authors: Coyne Jerry A. 
Published: September 2009

SummarySexual isolation between the sibling speciesD. simulansandD. mauritianais due largely to the rejection ofD. simulansmales byD. mauritianafemales. Genetic analysis shows that genes on the X and third chromosomes contribute to the differences between males causing sexual isolation, while the Y chromosome, second chromosome and cytoplasm have no effect. These chromosome effects differ from those observed in a previous analysis of sexual isolation in hybrid females, implying that different genes cause sexual isolation in the two sexes.
Mixed model approaches for diallel analysis based on a bio-model
Authors: Zhu Jun , Weir Bruce S. 
Published: September 2009

SummaryA MINQUE(l) procedure, which is minimum norm quadratic unbiased estimation (MINQUE) method with 1 for all the prior values, is suggested for estimating variance and covariance components in a bio-model for diallel crosses. Unbiasedness and efficiency of estimation were compared for MINQUE(l), restricted maximum likelihood (REML) and MINQUE(θ) which has parameter values for the prior values. MINQUE(l) is almost as efficient as MINQUE(θ) for unbiased estimation of genetic variance and covariance components. The bio-model is efficient and robust for estimating variance and covariance components for maternal and paternal effects as well as for nuclear effects. A procedure of adjusted unbiased prediction (AUP) is proposed for predicting random genetic effects in the bio-model. The jack-knife procedure is suggested for estimation of sampling variances of estimated variance and covariance components and of predicted genetic effects. Worked examples are given for estimation of variance and covariance components and for prediction of genetic merits.
Fitness patterns and phenotypic plasticity in a spatially heterogeneous environment
Authors: Zhivotovsky Lev A. , Feldman Marcus W. , Bergman Aviv 
Published: September 2009

SummaryWe analyse patterns of the means and variances of genotypic fitnesses across different niches in a randomly mating haploid population. The population inhabits a spatially heterogeneous environment where it is subject to mutation and weak multilocus additive selection, with different selection coefficients in different niches. Approximate analytical expressions are derived for the stationary mean and variance of genotypic fitnesses among the niches in terms of environmental and genetic parameters. As a special case, we analyse an environment described by a variablet, distributed among the niches with meant*and variance D*, and quadratic decrease in correlation between environments as a function of the difference in values oft. If the niches have the same qualities, the mean and variance of genotypic fitnesses evolve to be quadratic functions oftthat achieve their maximum and minimum, respectively, att*. With unequal niche qualities, these are non-polynomial functions that attain their extrema at different, usually intermediate values oft, although the coefficient of variation of the genotypic fitnesses still attains its minimum neart*. The functions involve the total mutation rate, the contribution of the loci to genotypic fitnesses, and the frequency and quality distributions of the niches. Thus, for this relatively simple model the norms of reaction may be calculated in terms of the detailed properties of the environmental heterogeneity, and the genetic system.
Two independent cis-acting elements regulate the sex- and tissue-specific expression ofyp3inDrosophila melanogaster
Authors: Ronaldson Elaine , Bownes Mary 
Published: September 2009

SummaryInDrosophila, the threeyolk protein(yp) genes are transcribed in a sex-, tissue- and developmentally specific manner, providing an ideal system in which to investigate the factors involved in their regulation. The yolk proteins are synthesized in the fat body of adult females, and in the ovarian follicle cells surrounding the developing oocyte during stages 8–10 of oogenesis. We report here an analysis of theyolk protein 3(yp3) gene and its flanking sequences by means of P-element mediated germ-line transformation and demonstrate that a 747 bp promoter region is sufficient to direct sex-specific expression in the female fat body and both the temporal- and cell-type-specificity of expression during oogenesis. Two elements that independently governyp3transcription in these tissues have been separated and no other sequences in the upstream, downstream or coding regions have been identified that are autonomously involved inyp3expression.
Rates of change of genetic parameters of body weight in selected mouse lines
Authors: Heath S. C. , Bulfield G. , Thompson R. , Keightley P. D. 
Published: September 2009

SummaryA method based on the animal model is described which allows the estimation of continuous changes in variance components over time using restricted maximum likelihood (REML). The method was applied to the analysis of a selection experiment in which a foundation population formed from a cross between two inbred strains of mice (C57BL/6J and DBA/2J) was divergently selected for 6 week body weight over 20 generations. The analysis suggested that there was an increase in phenotypic variance of about 50% in the low selected lines over the course of the experiment which was attributed to increases in the environmental and additive variance components. Variance changes in the High selected lines were generally smaller than in the Low lines, although there was an estimated 20% increase in the environmental variance. Simple models to explain these effects involving dominance, linkage and epistasis were explored. Testing which of these was responsible for the variance changes noted in this experiment (if any) is difficult, although the epistasis and dominance models require less stringent conditions than the linkage model, and the dominance model is supported by evidence of heterosis in the F1.
Pattern and frequency of nocodazole induced meiotic nondisjunction in oocytes of mice carrying the ‘tobacco mouse’ metacentric Rb(16.17)7Bnr
Authors: Everett C. A. , Searle J. B. 
Published: September 2009

SummaryOocytes from (C3H/HeH × 101/H)F1and Rb(16.17)7Bnr homozygous females were exposed to a range of doses of nocodazolein vitro. The spindle poison caused a dose dependent increase in metaphase I (MI) arrest and hyperploidy. A concentration of 0·03 μg/ml was found to induce a maximum hyperploid frequency of 3·1% and 11·6% respectively without a high level of MI arrest. Between 0·03 and 0·05 μg/ml MI arrest increased substantially and reached a frequency of approximately 90%. In a further experiment oocytes from Rb7 homozygous, heterozygous and 3H1 females were exposed to 0·03 μg/ml nocodazole 4, 6 or 8 h after the onset of maturation. The phase at which the spindle was inhibited resulted in a specific pattern of nondisjunction which in turn was dependent on whether the female carried an Rb metacentric. 3H1 oocytes gave a normally distributed pattern of increase in aneuploid frequency (over the spontaneous value) centering around a 6 h application. This was thought to be due to the interaction of chromosomes with the microtubules of the spindle during attachment and/or alignment. In contrast both Rb homozygotes and heterozygotes gave the same biphasic response, with a high frequency of aneuploidy in the oocytes when nocodazole was applied 4 and 8 h after the onset of maturation. In Rb homozygotes we demonstrated that the Rb bivalent underwent nondisjunction more frequently than the average acrocentric, when nocodazole was administered early. It can be assumed that the Rb trivalent in Rb heterozygotes showed a similar response. This early Rb specific effect, in combination with a delayed-version of the acrocentric effect found in the 3H1 mice was thought to generate the biphasic pattern. We discuss the implications of (a) the different meiotic behaviours of metacentrics and acrocentrics and (b) the meiotic delay in Rb mice.
Marker assisted selection for genetic improvement of animal populations when a single QTL is marked
Authors: Ruane J. , Colleau J. J. 
Published: September 2009

SummaryA Monte Carlo simulation study to evaluate the benefits of marker assisted selection (MAS) in small populations with one marked bi-allelic quantitative trait locus (QTL) is described. In the base generation, linkage phase equilibrium between the markers, QTL and polygenes was assumed and frequencies of 0·5 for the two QTL alleles were used. Six discrete generations of selection for a single character measured on both sexes followed. An additive genetic model was used with the QTL positioned midway between two highly polymorphic markers. Schemes were simulated with a distance of 10 cM between the QTL and either of the two markers and with the QTL explaining 1/8 of the total genetic variance in the base generation. Values of 0·5, 0·25 or 0·1 were assumed for the heritability. Eight males and 16, 32 or 64 females were selected each generation with each dam producing four sons and four daughters as candidates for the next generation. Animals were evaluated with a conventional BLUP animal model or with a model using marker information. MAS resulted in substantially higher QTL responses (4–54%), especially with low heritabilities, than conventional BLUP but lower polygenic responses (up to 4%) so that the overall effect on the total genetic response, although in the majority of cases favourable, was relatively small. With QTLs of larger size (explaining 25% of the genetic variance) comparable results were found. When the distance between the QTL and the markers was reduced to 2 cM, genetic responses were increased very slightly with a heritability of 0·5 whereas with a heritability of 0·1 responses were increased by up to 10%, compared with conventional BLUP. Results emphasize that MAS should be most useful for lowly heritable traits and that once QTLs for such traits have been identified the search for closely linked polymorphic markers should be intensified.
Commensalism, adaptation and gene flow: mosquitoes of theCulex pipienscomplex in different habitats
Authors: Chevillon Christine , Eritja Roger , Pasteur Nicole , Raymond Michel 
Published: September 2009

SummaryTwo ecotypes have been described forCulex pipiensmosquitoes of the temperate zone: a human commensal type and a feral type, but their degree of evolutionary differentiation and taxonomic status are still unclear. The commensal form is characterized by life-history traits probably adaptive to underground man-made environments. This situation has sometimes been considered as an example of recent speciation although the existence of intermediate forms indicates that the balance between gene flow and disruptive selection should first be assessed. The present study was concerned with (1) the determination of biological traits involved in adaptation to commensalism, and (2) the pattern of gene flow within and between ecotypes in a restricted area. It was found that (1) significant differences in biological traits exist between mosquitoes from different habitats, (2) characteristics of the commensal type are not universal in mosquitoes from underground man-made habitats, (3) allozyme markers do not clearly differentiate ecotypes and (4) insecticide resistance genes, which reveal recent migration, occur in each ecotype. These results are discussed in the context of possible speciation due to commensalism.
The distribution of transposable elements on X chromosomes from a natural population ofDrosophila simulans
Authors: Nuzhdin Sergey V. 
Published: September 2009

SummaryThe distribution of 13 transposable element families along 15 X chromosomes from an African natural population ofDrosophila simulanswas determined byin situhybridization to polytene chromosomes. The transposable elements cloned fromDrosophila melanogasterall hybridized withDrosophila simulanschromosomes. The number of copies per family was 3·5 times lower in the latter species and correlated with the copy number per family inDrosophila melanogaster. With the exception of297, the copy number per chromosome followed a Poisson distribution. Element frequencies per chromosome band were generally low. However, several sites of the distal region and the base of the X chromosome had high frequencies of occupation. Elements had higher abundance at the base of the chromosome compared to distal regions. Overall, the distribution of transposable elements inDrosophila simulansis similar to that found inDrosophila melanogaster. These data provide evidence for the operation of a force (or forces) opposing transpositional increase in copy number, and that this force is weaker at the bases of chromosomes, consistent with the idea that recombination between elements at non-homologous sites contains TE copy number. The reduction in copy number of all TE families inDrosophila simulanscompared toDrosophila melanogastercan be explained by stronger selection against transposable element multiplication and/or lower rates of transposition inDrosophila simulans.
The genetics of tasting in mice VII. Glycine revisited, and the chromosomal location ofSacandSoa
Authors: Lush I. E. , Hornigold N. , King P. , Stoye J. P. 
Published: September 2009

SummaryPrevious work which appeared to show that some strains of mice taste glycine solutions as bitter has been found to be in error. The bitterness came from copper glycinate which formed in the brass drinking spouts. Taste testing with copper glycinate shows that the genetical data identifying the geneGlbare still valid. The close linkage ofGlbandRuahas been confirmed. Most strains of mice prefer glycine solution to water, presumably because the glycine tastes sweet. The degree of preference for glycine is correlated with the degree of preference for other sweet substances such as saccharin or acesulfame. The genedpaappears not to be involved.The sweetness tasting geneSachas been mapped to chromosome 4 at 8·1 ± 3·4 cM distal toNppa(formerlyPnd). The bitterness tasting geneSoais very closely linked toPrpon chromosome 6 (no recombinants among 67 backcross progeny). It is suggested that the sweetness and bitterness tasting genes have descended from a common ancestral tasting gene which existed before the tetraploidization of the genome which took place in early vertebrate evolution.
The cellular basis for interaction of sterility factors in the mousethaplotype
Authors: Johnson Linda R. , Pilder Stephen H. , Olds-Clarke Patricia 
Published: September 2009

SummaryThethaplotypes are variant forms of the proximal one-third of chromosome 17 in the mouse. They contain four inversions (relative to the wildtype DNA) extending over most of this region and house a number of male sterility factors. Males carrying two completethaplotypes (t/t) are sterile, as are males homozygous forS2, the sterility factor located in the most distal (relative to the centromere) inversion. Males homozygous for the sterility factorS1, located in the most proximal inversion, are not sterile; however, if such a male also is heterozygous for other sterility factors, then sterility results. It has been suggested therefore that homozygosity forS1enhances the detrimental action of other sterility factors. Sperm fromt/tmales have severe motility defects and are unable to penetrate investment-free eggs, while sperm from fertilet/+ mice have less serious motility defects and exhibit a delay in penetration of investment-free eggs. To determine whether homozygosity forS1enhances the cellular defects exhibited by sperm from mice heterozygous for other sterility factors, we compared the motility and egg-penetrating ability of sperm from fertile mice homozygous forS1to that of sperm from mice carrying one completethaplotype and one proximal or distal partialthaplotype. The data suggest that sperm from males carrying a proximal partialthaplotype and a completethaplotype have serious defects in motility and penetration of the investment-free egg, and support the hypothesis thatS1enhances the detrimental effects of other sterility factors within thethaplotype.
Induction of unstable alleles at the temperature-sensitiveVirescent-1gene of maize using the transposable elementDissociation
Authors: Cerioli Sergio , Ballarini Stefania , Uhrig Helmut , Scalzotto Eugenio , Marocco Adriano 
Published: September 2009

SummaryTranspositive mutagenesis was employed to prepare genetic strains useful in cloning theVirescent-1locus (V1) of maize. A stepwise approach was used based on: (1) the isolation of putative insertion phenotypes (62 cases); (2) the verification of the genetic nature of the selected events (36v1-mmutant alleles induced); (3) the accurate genetic study of 11 alleles; (4) the genetic assessment that the allelesv1-m1andv1-m4are due to the insertion ofa Dselement into the locusV1; (5) the proof that aDs-like DNA element induces the inactivation of the wild type function in the allelev1-m1. The phenotype of the unstable alleles, studied by germinating and keeping maize seedlings at the temperature of 18 °C, are the following: allelesv1-m1, v1-m9, v1-m11, v1-m17andv1-m18showing a few revertant green sectors on their leaves;v1-m4exhibiting a reverse type of variegation; allelesv1-m2andv1-m13with a coarse pattern of variegation; allelesv1-m12, v1-m21andv1-m23frequently showing leaves part green with white stripes and part white with green stripes. For the alleles studied, in addition to somatic instability, germinal reversions also occurred. In some cases, these reversions resulted in stable derivatives with a different colour from that of the wild-type (‘near green’ or pale phenotypes). The results presented not only allow thev1-m1allele to be chosen as a starting material for cloning theV1locus, but also define the molecular strategy to be followed.
Response to selection from new mutation and effective size of partially inbred populations. I. Theoretical results
Authors: Caballero Armando , Santiago Enrique 
Published: September 2009

SummaryThe effects of partial inbreeding on effective population size and rates of fixation of mutant genes are investigated in selected populations. Truncation selection and an infinitesimal model of gene effects for the selected trait are assumed. Predictions of effective size under this model are given for partial selfing and partial full-sib mating and an extension to a more general model is outlined. The joint effect of selection and partial inbreeding causes a large reduction in the effective size relative to the case of random mating. This effect is especially remarkable for small amounts of selected genetic variation. For example, for initial heritability 0·1 and proportion selected 1/6, the ratio of effective size to population size is 0·10 in populations with about 90% selfing while it is 0·85 in random mating populations. The consequence is a reduction in the fixation probability of favourable genes and, therefore, a reduction in the final response to selection. Stochastic simulations are used to investigate the effects of partial inbreeding and selection on fixation and extinction rates of genes of large effect and of recessive lethals with effects on the selected trait. For genes of very large effect, the effective size is not a critical factor and it is expected that partial inbreeding will be efficient in increasing fixation rates of recessive mutants. Lethal recessives are eliminated more frequently and their equilibrium frequency is lower under partial inbreeding, but only when their effects on the heterozygote are not very large.