bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of transgenic strains ofDrosophila melanogastercontaining I transposable elements fromDrosophila teissieri
Authors: Vaury Chantal , Pélisson Alain , Abad Pierre , Bucheton Alain
Published: September 2009

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

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

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

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

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

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

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

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

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

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

The dominant gene Fused (Fu) produces skeletal abnormalities during embryonic development. It was previously shown that C57BL/6 mice contain a suppressor ofFu, which acts after fertilization. Chimaeras were used to study whether this gene would suppress theFuphenotype after the 8-cell stage of embryo development. We found no effect of the suppressor gene onFuphenotype (its degree and frequency of expression) in chimaeric mice. We conclude that either the suppressor gene from C57BL/6 mice can only influenceFuexpression at the intracellular level orFuexpression is determined before the 8-cell embryonic stage.
The effect of background selection against deleterious mutations on weakly selected, linked variants
Authors: Charlesworth Brian
Published: September 2009

This paper analyses the effects of selection against deleterious alleles maintained by mutation (‘ background selection’) on rates of evolution and levels of genetic diversity at weakly selected, completely linked, loci. General formulae are derived for the expected rates of gene substitution and genetic diversity, relative to the neutral case, as a function of selection and dominance coefficients at the loci in question, and of the frequency of gametes that are free of deleterious mutations with respect to the loci responsible for background selection. As in the neutral case, most effects of background selection can be predicted by considering the effective size of the population to be multiplied by the frequency of mutation-free gametes. Levels of genetic diversity can be sharply reduced by background selection, with the result that values for sites under selection approach those for neutral variants subject to the same regime of background selection. Rates of fixation of slightly deleterious mutations are increased by background selection, and rates of fixation of advantageous mutations are reduced. The properties of sex-linked and autosomal asexual and self-fertilizing populations are considered. The implications of these results for the interpretation of studies of molecular evolution and variation are discussed.
An application of population genetic theory to synonymous gene sequence evolution in the human immunodeficiency virus (HIV)
Authors: Kelly John K.
Published: September 2009

A population genetic model is developed and then applied to the synonymous gene sequence variation observed in samples of the Human Immunodeficiency Virus Type 1 (HIV-1). The samples, which were taken from several previous studies, contain sequences of the envelope glycoprotein gene (gp 120) of HIV-1. This analysis suggests that the viral population within an infected patient at any specific time is likely to be composed of close relatives. The viruses in a sample are likely to share a recent common ancestor probably due to consistent positive selection for non-synonymous mutations coupled with low recombination in this region of the genome. There is no substantial difference in synonymous evolutionary rate between samples of sequences obtained from Peripheral Blood Mononucleate Cells (PBMCs) and samples taken from blood plasma. This is likely to be due to the high rate of migration between these 2 HIV sub-populations. The mutation rate for the genetic region examined is estimated at 9·20 × 10−4per site per month. Under the assumptions of the estimation procedure, this estimate can be bounded between 8·50 and 9·91 × 10−4with 95% confidence. When coupled with direct estimates of mutation rate, the rate of synonymous evolution suggests that the mean number of generations per month for HIV-1in vivois between 1 and 4.
Spontaneous sex reversal inPleurodeles waltl(urodele amphibia): analysis of its inheritance
Authors: Collenot Alain , Durand Danielle , Lauthier Michel , Dorazi Robert , Lacroix Jean-Claude , Dournon Christian
Published: September 2009

Up to now, no case of spontaneous sex reversal has been described in the urodele amphibianPleurodeles waltlreared at ambient temperature. However in offspring reared under laboratory conditions, males, females but also intersex individuals were obtained. The males, some females and the intersexes had the ZZ male genotype identified through a test performed with a sex-linked enzyme. The other females had the ZW female genotype. Using the animals of this particular strain, an offspring analysis was made on crosses between, respectively, ZZ males and ZW females, ZZ males and ZZ females, and ZZ intersexes and ZZ males or females. All these crosses gave ZZ males, ZZ females and ZZ intersexes. The spontaneous complete or partial sex reversal is inheritable, but the genetic mechanism of this inheritance has not yet been elucidated.
An exact test for neutrality based on the Ewens sampling distribution
Authors: Slatkin Montgomery
Published: September 2009

Using the Ewens sampling distribution of selectively neutral alleles in a finite population, it is possible to develop an exact test of neutrality by finding the probability of each configuration with the same sample size and observed number of allelic classes. The exact test provides the probability of obtaining a configuration with the same or smaller probability as the observed configuration under the null hypothesis. The results from the exact test may be quite different from those from the Ewens—Watterson test based on the homozygosity in the sample. The advantages and disadvantages of using an exact test in this and other population genetic contexts are discussed.
Selection on reaction norms, genetic correlations and constraints
Authors: Van Tienderen Peter H. , Koelewijn Hans P.
Published: September 2009

Two approaches to the evolution of phenotypic plasticity in heterogeneous environments have recently been put forward. The first focuses on selection on the character expression within each environment; plasticity is seen as a by-product of local selection in various habitats. The second approach focuses on selection on the parameters of the response function of genotypes, and selection is thought to change the frequencies of ‘plasticity’ genes that affect the function. This paper discusses the relationship between the two approaches, with emphasis on applications. A method is described that allows switching from one approach to the other. It is argued that character state and reaction norm approaches, while to a large extent interchangeable, usually differ in the response function chosen. This choice, however, may strongly affect the biological interpretation. The methods outlined in this paper permit one to look at the data from different perspectives in order to avoid this danger.
Estimation of inbreeding coefficients from genotypic data on multiple alleles, and application to estimation of clonality in malaria parasites
Authors: Hill William G. , Babiker Hamza A. , Ranford-Cartwright Lisa C. , Walliker David
Published: September 2009

Methods for estimating probability of identity by descent (f) are derived for data on numbers of genotypes at single loci and at pairs of loci with many alleles at each locus. The methods are general, but are specifically applied to data on genotype frequencies in zygotes of the malaria parasite sampled from its mosquito host in order to find the extent of outcrossing in the parasite and the degree of clonality in populations. It is assumed that zygotes are the outcome either of gametes of the same clone, in which they are identical at all loci, or are products of two random, unrelated clones. From the estimate offan effective number of clones per human host can also be derived. ForPlasmodium falciparumfrom a Tanzanian village, estimates offare 0·33 from data on zygote frequencies at two multiallelic loci, indicating that two-thirds of zygotes produce recombinant types.
Comparative population structuring of molecular and allozyme variation ofDrosophila melanogaster Adhbetween Europe, West Africa and East Africa
Authors: Bénassi Véronique , Veuille Michel
Published: September 2009

Restriction enzyme molecular variation inDrosophila melanogaster Adhwas compared between three natural populations from Europe, West Africa and East Africa. The frequency distribution of silent variation in theslowallele was compatible with the neutral model in all three samples. The number of haplotypes in East Africa was significantly higher than in the other two populations. The largest divergence, as measured byFst, was between the East African population and a group made up from the West African, the European, and previously studied American populations. We suggest that a split first occurred within African populations at least 44000 years ago. European populations separated from West Africa more recently, between the last glacial maximum and the post-glacial optimum, 18000 to 8000 years ago. We suggest that this species was domesticated recently relative to human evolution, possibly with the advent of agriculture. Population differentiation with respect to the two allozymes,fastandslow, does not follow the geographical pattern of silent variation. It opposes European to both African populations, and probably results from selection for adaptation to alcohol in recent temperate populations.
Dynamics of unconditionally deleterious mutations: Gaussian approximation and soft selection
Authors: Kondrashov Alexey S.
Published: September 2009

This paper studies the influence of two opposite forces, unidirectional unconditionally deleterious mutations and directional selection against them, on an amphimictic population. Mutant alleles are assumed to be equally deleterious and rare, so that homozygous mutations can be ignored. Thus, a genotype is completely described by its value with respect to a quantitative traitx, the number of mutations it carries, while a population is described by its distributionp(x) with meanM[p] and varianceV[p] = σ2[p]. When mutations are only slightly deleterious, so thatM» 1, before selectionp(x) is close to Gaussian with any mode of selection. I assume that selection is soft in the sense that the fitness of a genotype depends on the difference between its value ofxandM, in units of σ. This leads to a simple system of equations connecting the values ofMandVin successive generations. This system has a unique and stable equilibrium,whereUis the genomic deleterious mutation rate, δ is the selection differential forxin units of σ, andpis the ratio of variances ofp(x) after and before selection. Both δ and ρ are parameters of the mode of soft selection, and do not depend onMorV. In an equilibrium population, the selection coefficient against a mutant allele is ŝ = δ2[U(2–ρ)]−1. The mutation load can be tolerable only if the genome degradation rate υ =U/σ is below 2. Other features of mutation-selection equilibrium are also discussed.
Partial deletion of the Y chromosome removes the effect of paternal genome imprinting on periovum sensitivity to hyaluronidase in mice
Authors: Styrna Józefa
Published: September 2009

Cumulus-oocyte complexes from the two consomic strains of mice, B10. BR and BIO.BR-Ydel (with a partial deletion of the Y chromosome) and the BALB/c strain, as well as reciprocal Fl and F2 hybrids, were tested for their susceptibility to attack by hyaluronidase. The cumulus cell dispersal was significantly more rapid in the eggs of B10.BR females and of Fl and F2 hybrid females sired by the B10.BR males than in those of BALB/c females and hybrids sired by BALB/c males. These results confirm the earlier data of Bander et al. (1989) which were interpreted as evidence of paternal imprinting of the C57BL genome. In contrast, cumulus cell dispersal in the eggs of females sired by BIO.BR-Ydel males was significantly slower than in females sired by B10.BR males, and did not differ from that in the BALB/c strain. The results suggest that the partial deletion of the Y chromosome abolished the effect of paternal genome imprinting which is observed in the B10.BR strain.
Mitochondrial inheritance inAspergillus nidulans
Authors: Coenen Alex , Croft Jim H. , Slakhorst Marijke , Debets Fons , Hoekstra Rolf
Published: September 2009

Mitochondrial chloramphenicol and oligomycin resistance mutations were used to investigate mitochondrial inheritance inA. nidulans. Mitochondrial RFLPs could not be used to distinguish between paternal and maternal mitochondria because none were detected in the 54 isolates investigated. Several thousand ascospores from each of 111 hybrid cleistothecia from 21 different crosses between 7 heterokaryon incompatible isolates were tested for biparental inheritance. All mitochondrial inheritance was strictly uniparental. Not one instance of paternal inheritance of mitochondria was observed. The implications of our results for the theory that uniparental inheritance evolved to avoid cytoplasmic conflictare discussed. Possible explanations for the maintenance of strict uniparental inheritance of mitochondria in an inbreeding homothallic organism are suggested. The chloramphenicol resistance marker was inherited preferentially to the oligomycin resistance marker probably due to the inhibited energy production of mitochondria with the oligomycin resistance mutation. The maternal parent was determined for 93 hybrid cleistothecia from 17 crosses between 7 different strains. Contraryto previous reportsA. nidulansstrains functioned as both maternal and paternal parent in most crosses.
Estimators for pairwise relatedness and individual inbreeding coefficients
Authors: Ritland Kermit
Published: September 2009

Method-of-moments estimators (MMEs) for the two-gene coefficients of relationship and inbreeding, and for thxe four-gene Cotterman coefficients, are described. These estimators, which use co-dominant genetic markers, are most appropriate for estimating pairwise relatedness or individual inbreeding coefficients, as opposed to their mean values in a group. This is because, compared to the maximum likelihood estimate (MLE), they show reduced small-sample bias and lack distributional assumptions. The ‘efficient’ MME is an optimally weighted average of estimates given by each allele at each locus. Generally, weights must be computed numerically, but if true coefficients are assumed zero, simplifiedestimators are obtained whose relative efficiencies are quite high. Population gene frequency is assumed to be assayed ina larger, ‘reference population’ sample, and the biases introduced by small reference samples and/or genetic drift of the reference population are discussed. Individual-level estimates of relatedness or inbreeding, while displaying high variance, are useful in several applications as a covariate in population studies.
Genetic analysis ofDrosophila virilissex pheromone: genetic mapping of the locus producing Z-(ll)-pentacosene
Authors: Doi Motomichi , Tomaru Masatoshi , Matsubayashi Hiroshi , Yamanoi Kiyo , Oguma Yuzuru
Published: September 2009

Z-(ll)-pentacosene,Drosophila virilissex pheromone, is predominant among the female cuticular hydrocarbons and can elicit male courtship behaviours. To evaluate the genetic basis of its production, interspecific crosses betweenD. novamexicanaand genetically markedD. viriliswere made and hydrocarbon profiles of their backcross progeny were analysed. The production of Z-(ll)-pentacosene was autosomally controlled and was recessive. Of the sixD. virilischromosomes only the second and the third chromosomes showed significant contributions to sex pheromone production, and acted additively. Analysis of recombinant females indicated that the locus on the second chromosome mapped to the proximity of position 2–218.
Stability and genetic basis of variability of phally polymorphism in natural populations of the self-fertile freshwater snailBulinus truncatus
Authors: Doums Claudie , Labbo Rabiou , Jarne Philippe
Published: September 2009

We investigated the genetic variability for phally polymorphism within and between natural populations of the hermaphrodite self-fertile freshwater snailBulinus truncatus. Phally polymorphism is characterized by the co-occurrence in natural populations of regular hermaphrodite individuals (euphallic) and individuals deprived of the male copulatory organ (aphallic). The two morphs can both self-fertilize and outcross. However, aphallic individuals cannot outcross as males. We examined the variation of the aphally ratio in 22 natural populations from Niger over two successive years. During the second years, populations were sampled three times at 3 week intervals. The aphally ratio was highly variable among populations at a given sampling data and remained relatively stable over time. For 10 of these populations, one population from Corsica and two from Sardinia, we also estimated the between- and within- population variability, analysing the aphally ratio of 346 families under laboratory conditions. The aphally ratio varied significantly among populations and was highly correlated with the aphally ratio of the natural populations. Some within-population variability, associated with a high value of the broad sense heritability, was observed in four populations out of 13. In these populations, aphallic individuals produced significantly more aphallic offspring than euphallic individuals. Our results indicate a strong genetic basis for aphally, with large genetic differences among populations and some genetic variability for aphally within populations. We discuss the adaptive and stochastic factors that may shape the distribution of the genetic variability for aphally.
Pleiotropy as a factor maintaining genetic variation in quantitative characters under stabilizing selection
Authors: Gimelfarb A.
Published: September 2009

A model of pleiotropy withNdiallelic loci contributing additively toNquantitative traits and stabilizing selection acting on each of the traits is considered. Every locus has a major contribution to one trait and a minor contribution to the rest of them, while every trait is controlled by one major locus and N−1 minor loci. It is demonstrated that a stable equilibrium with the allelic frequency equal to 0·5 in allNloci can be maintained in such a model for a wide range of parameters. Such a ‘totally polymorphic’ equilibrium is maintained for practically any strength of selection and any recombination, if the relative contribution by a minor locus to a trait is less than 20 % of the contribution by a major locus. The dynamic behaviour of the model is shown to be quite complex with a possibility under sufficiently strong selection of multiple stable equilibria and positive linkage disequilibria between loci. It is also suggested that pleiotropy among loci controlling traits experiencing direct selection can be responsible for apparent selection on neutral traits also controlled by these loci.
Distortion of Mendelian recovery ratio for a mouse HSR is caused by maternal and zygotic effects
Authors: Weichenhan Dieter , Traut Walther , Kunze Bärbel , Winking Heinz
Published: September 2009

An HSR in chromosome 1 which is found in many feral populations ofMus musculus domesticuswas shown in previous studies to consist of a high-copy long-range repeat cluster. One such cluster,MUT, showed distorted transmission ratios when introduced by female parents.MUT/ + offspring were preferentially recovered at the expense of + / + embryos in the progeny of ♀MUT/+ x♂ +/+ but were found at the expected 1:1 ratio in reciprocal crosses. Preferential recovery of maternal MUT was due to lethality of postimplantation + /+ embryos. There was no distortion of the recovery ratio inMUT/+ xMUT/MUTprogeny: maternalMUTand + clusters were present among live implants at a 1:1 ratio. Maternal and zygotic effects therefore contribute to the phenomenon. The mechanism of their interaction is unknown.
Evolution of amphimixis and recombination under fluctuating selection in one and many traits
Authors: Kondrashov Alexey S. , Yampolsky Lev Yu.
Published: September 2009

Both stabilizing and directional selection acting on one or many quantitative traits usually reduce the genetic variance in a polymorphic population. Amphimixis and recombination restore the variance, pushing it closer to its value under linkage equilibrium. They thus increase the response of the population to fluctuating selection and decrease the genetic load when the mean phenotype is far from optimum. Amphimixis can have a short-term advantage over apomixis if selection fluctuates frequently and widely, so that every genotype often has a low fitness. Such selection causes high genetic variance due to frequent allele substitutions, and a high load even with amphimixis. Recombination in an amphimictic population is maintained only if selection is usually strong and effectively directional. A modifier allele causing free recombination can have a significant advantage only if fluctuations of selection are such that the load is substantial. With smaller fluctuations, an intermediate recombination rate can be established, either due to fixation of alleles that cause such a rate or due to the stable coexistence of alleles causing high and low recombination. If many traits simultaneously are under fluctuating selection, amphimixis and recombination can be maintained when selection associated with individual traits is weaker and the changes in their mean values are smaller than with a single trait. Still, the range of changes of the fitness optima in each trait must be at least of the order of the trait's standard deviation, and the total load must be high.
Mapping quantitative trait loci using four-way crosses
Authors: Xu Shizhong
Published: September 2009

In plant species, typical gene mapping strategies use populations initiated from crosses between two inbred lines. However, schemes including more than two parents could be used. In this paper, a new approach is introduced which uses a four-way cross population derived from four inbred lines. The four-way cross design for mapping quantitative trait loci (QTLs) provides tests for QTL segregation in four lines simultaneously in one experiment. Therefore, it is a more economical strategy than oneusing line crosses between only two lines. The new strategy also increases the probability of detecting QTLs if they segregate in one line cross but not in the other. A multiple linear regression analysis is used for QTL detection. It is proven that the expected residual variance from the regression analysis differs from the pure environmental variance. Correction for the bias is proposed and verified by computer simulations.
A 1·5 kb direct repeat sequence flanks thesuppressor of forkedgene at the euchromatin–heterochromatin boundary of theDrosophila melanogasterX chromosome
Authors: Tudor Mark , Mitchelson Andrew , O'hare Kevin
Published: September 2009

A 1·5 kilobasepair repeated DNA sequence is duplicated in direct orientation so as to flank thesuppressor of forkedgene in the euchromatin–heterochromatin transition region on the X chromosome ofDrosophila melanogaster. These two copies are almost identical, but DNA blotting, analysis of cloned sequences and database searches show that elsewhere in the genome, homologous sequences are poorly conserved. They are often associated with other repeats, suggesting that they may belong to a scrambled and clustered middle repetitive DNA family. The sequences do not appear to be related to transposable elements and their location in different strains is conserved.In situhybridization to metaphase chromosomes shows that homologous sequences are concentrated in the pericentric regions of the autosomes and the X chromosome. The sequences are not significantly under-represented in DNA from polytene tissue and must lie in the replicated regions of polytene chromosomes. The almost perfect conservation of the two repeats aroundsuppressor of forkedinD. melanogastersuggests they arose by duplication or gene conversion. Suppression of recombination in this chromosomal region presumably allows this unusual organization to be stably maintained. In the X-ray induced allele,suppressor of forked-L26, the sequence between the repeats, including the gene, and one copy of the repeat have been deleted.
A correction to the exact test based on the Ewens sampling distribution
Authors: Slatkin Montgomery
Published: September 2009

The exact test for neutrality based on the Ewens sampling distribution described previously (Slatkin, 1994) is not correct. The problem is that the test as described is based on the probability of the ordered configuration of numbers of alleles, while it should be based on the probability of the unordered configuration. The correctly implemented exact test leads to results that are similar to those from the homozygosity test proposed by Watterson (1977) for relatively small sample sizes but can still differ substantially for larger sample sizes. Programs to perform the exact test are available from the author.
Linkage map of random amplified polymorphic DNAs (RAPDs) in the silkworm,Bombyx mori
Authors: Promboon Amornrat , Shimada Toru , Fujiwara Haruhiko , Kobayashi Masahiko
Published: September 2009

We have constructed a linkage map of random amplified polymorphic DNAs (RAPDs) inBombyx mori. We screened 320 10-mer primers, and found 243 clear polymorphic bands between C108 and p50 strains. In the F2generation, segregation ratios of 168 bands were nearly 3:1 in a chi square test, showing Mendelian inheritance. The MAPMAKER program sorted 168 bands into 29 linkage groups and 10 unlinked loci at minimum LOD score 3·0, and determined orders of loci in each group, which contained 2–11 markers. It also detected typing errors in our data. We calculated map distances between pairs of neighbouring loci using recombination values in males and the Kosambi mapping function. Our RAPD map consists of 169 loci including theplocus, and the sum of map distances is approximately 900 cM. Linkage groups 1 and 2 of our map correspond to chromosomes 1 and 2 on the conventional linkage map because of linkage to sex andp, respectively.
Low rates of proviral integration in SWR/J–RF/J hybrid mice
Authors: Kay Simon J. E. , Keightley Peter D.
Published: September 2009

A high frequency of proviral acquisition has previously been reported in the offspring of SWR/J–RF/J hybrid mice. In the present study, it was investigated whether this proviral acquisition would be useful for large-scale insertional mutagenesis studies. A population of SWR/J–RF/J hybrid mice with a predominantly SWR/J background was created. Lines of mice with such a background and partially congenic for two active proviruses from the RF/J strain were generated (the insert lines). Control lines were derived from mice which had no proviral loci but had an otherwise similar genetic background. DNA samples of mice in the insert lines were screened for the appearance of new proviral loci by Southern hybridization. The rate of proviral acquisition, calculated from the observed number of new proviral loci was 0·023 new proviruses per mouse. This rate is lower than found in previous studies and too low for large-scale insertional mutagenesis studies. A sensitivity experiment indicated that there was adequate detection of new proviral loci.The number of segregating proviruses was consistent with the number of newly acquired proviruses actually detected. Two additional crosses between mice in the insert lines and SWR/J mice were performed. The rate of proviral acquisition was greatly increased when SWR/J females were initially mated to insert mice, but remained unchanged when SWR/J males were used. This suggested that mice in the insert lines had acquired a maternally transmitted factor, which was suppressing viral expression and thus reducing the rate of proviral acquisition.
Population structure, fitness surfaces, and linkage in the shifting balance process
Authors: Bergman Aviv , Goldstein David B. , Holsinger Kent E. , Feldman Marcus W.
Published: September 2009

Wright first introduced the idea that random genetic drift and classical mass-action selection might combine in such a way as to allow populations to find the highest peak in complicated adaptive surfaces. His theory assumes large but structured populations, in which mating is spatially local. If gene flow is sufficiently low, and the subpopulations (demes) are small enough, they will be subject to genetic drift. Distant demes drift independently, allowing many independent searches of the adaptive surface to take place. A deme that has shifted to a higher peak can, by emigration, cause the rest of the demes to shift to the higher peak. The probability of this shift depends on the migration rate. Previous studies have concluded that very little migration is necessary to effect the shift in adaptive peaks that characterizes the last phase of Wright's Shifting Balance Process (SBP).

Here we present the results of a computer study that investigates the roles of dispersal distance, the degree of epistasis in the fitness surface, and recombination on the shifting balance process. In particular, we measure their effect on the population's mean fitness. We show that over a range of dispersal distances the advantage of the SBP is a monotonically increasing function of the amount of epistasis. Our results show that the extent of dispersal that results in the greatest effect of the SBP in increasing mean fitness depends on the extent of epistasis. Finally, for low levels of epistasis, higher recombination performs better, while for intermediate levels, lower recombination results in a greater advantage of the SBP.
The role of passive migration in the dispersal of resistance genes in Culex pipiens quinquefasciatus within French Polynesia
Authors: Pasteur Nicole , Marquine Maité , Rousset François , Failloux Anna-Bella , Chevillon Christine , Raymond Michel
Published: September 2009

We have investigated the distribution of resistance genes in relation to genetic structure and gene flow between various islands of French Polynesia in Culex pipiens quinquefasciatus. We show that (1) resistance to organophosphorous insecticides, mediated by A2–B2 esterases, is present in all islands, (2) A2–B2 frequency decreases as distance from Tahiti increases, and (3) genetic differentiation (measured as estimates of the Fst, parameter from allozyme polymorphism) between islands is significantly correlated to geographic distances which is also correlated to air or sea commercial traffic. These data are discussed in relation to A2–B2 invasion of French Polynesian islands.
Genotype × environment interaction in Tribolium castaneum
Authors: Kidwell J. F. , Freeman A. E. , Haverland L. H. , Rolfes G. M. H.
Published: September 2009

An experiment was conducted with the flour beetle, Tribolium castaneum to investigate genotype-environment interaction. Ninety-two matings of one male and three females were made at random from a large panmictic population. The females were transferred to individual containers after 4 days. Six daughters were randomly selected from each sire–dam pair and individually mated to unrelated males. Three of the six were placed in an incubator (33·3°C., 45% relative humidity) and three in a cabinet at room conditions (22·2–26·7°C., 30–35% relative humidity) and allowed to produce eggs during a 3-day period. Progeny were counted as pupae and larvae. The traits studied were number of pupae and number of pupae plus number of larvae. A transformation to (X +1)½ was required. A conventional least-squares model was employed, and a large environmental effect was observed. In the incubator the mean number of pupae was 13·4 and of pupae + larvae was 20·1 while the corresponding figures for room conditions were 3·3 and 9·2. Genotype-environment interaction accounted for 3·7 to 6·7% of the total variance for (pupae + 1)½ and 2·1 to 8·3% for (pupae + larvae+ 1)½. Heritability of the traits was essentially the same in both environments. The interaction was due to an increasing difference between environments in production associated with increasing breeding values of the sire, and to small changes in rank of breeding values on the two environments. As a result of the interaction, selection in one environment for production on the other would be expected to be only 71 to 72% as effective as direct selection for (pupae + 1)½ and 62 to 86% for (pupae + larvae + 1)½ even though the fraction of the total variance attributed to genotype-environmental interaction was less than 10%.
Rose comb: an example of operational over-dominance in the domestic fowl
Authors: Fox Thomas W. , Crawford Roy D. , Smyth J. Robert
Published: September 2009

The pleiotropic effect of the rose-comb gene (R) on fertility when combined with artificial selection against the single-comb type (r) results in an interesting example of operational over-dominance. An evaluation of the equilibrium frequency of the rose-comb gene based on this over-dominance concept provides a plausible explanation for the relatively high frequency of single-comb birds appearing in the Wyandotte breed of fowls.