bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of thewhiteallele of themilocus on coat pigmentation in chimeric mice
Authors: Konyukhov Boris V. , Kindyakov Boris N. , Malinina Natalia A.
Published: September 2009

To investigate the cellular action of theMiωhallele in the mouse with regard to its effects upon coat color patterns, we generated a series of aggregation chimeras, using embryos that differ in theirmilocus genotype. We have obtained 11 chimerasMiωh/ +C/C↔ + / +c/cand 8 chimeras + / +C/C↔ + / +c/c. Chimerism was determined by coat and retinal pigment epithelium mosaicism and by the electrophoretic analysis of GPI-1 isoenzymes. InMiωh/+C/C↔, +/+c/cmice white coat color prevailed due to the higher percentage of unpigmented areas and the higher percentage of unpigmented hairs in pigmented areas. Our data indicate that a singleMiωhgene dose decreases the melanoblast proliferative activity, causing the lightening of coat pigmentation. InMiωh/ +C/C↔+/+c/cmice a few pigmented hairs were often detected on the belly whereMiωh/ + mice always had a white spot. This suggests that in the chimeras the presence of some non-Miωhcells in the skin of the belly allows pigment cells to develop. Using embryos of two substrains ofMiωh/Miωhmice that differ in their Gpi-1 locus genotype we have produced 8Miωh/ + ↔Miωh/Miωhchimeras. In all these chimeras coat color patterns resembled those ofMiωh/ + heterozygotes despite the higher percentage of theMiwh/Miωhcomponent in three chimeras. Mosaic hairs were absent in the chimeras. This shows that the chimeras have only oneMiωh/ + melanoblast population which actively proliferates and colonizes almost all hair follicles. Thus theMiωh/Miωhdermis and epidermis do not suppress proliferation and differentiation of theMiωh/ + melanoblasts except the certain area on the belly.
The inheritance of female mating behaviour in the seaweed fly,Coelopa frigida
Authors: Gilburn André S. , Day Thomas H.
Published: September 2009

In order to understand the evolution of female mate preferences it is important to determine whether the genes for the preference and those for the preferred character are linked. It has previously been shown that female preference in the seaweed fly,Coelopa frigida, varies with the αβ inversion system on chromosome I. This inversion system is known to genetically determine, at least in part, the male preferred character, large size. This study was undertaken to determine whether the genes determining mate preferences, as well as those determining female receptivity, co-inherit with the inversion. In the full sibs of animals recently collected from a natural population in Sweden it is shown that high acceptance rate and strong preference for large male size both co-segregate with the α form of the inversion, and that low acceptance rate and a weak preference for large size co-segregate with the β form of the inversion. Both sets of genes appear to be located in or near the αβ inversion. The heterogeneity between crosses suggests the natural population from which the animals were collected was polymorphic for behavioural genes on the β haplotype. Crosses involving animals that had been in laboratory culture for seven generations indicated that variation in female mating behaviour had been lost. Possible reasons for the apparent instability of such behaviour are discussed.
Segregation variance after hybridization of isolated populations
Authors: Slatkin Montgomery , Lande Russell
Published: September 2009

We develop a model to predict the increase in genetic variance of a quantitative character in a hybrid population produced by crossing two previously isolated populations of the same species. The increase in variance in the F2hybrids, the ‘segregation variance’, is caused by differences in the average allelic effects at each locus and by linkage disequilibrium among loci. We focus on the case in which the character is additively based and the average value of the character does not differ in the two populations. In that case the predicted segregation variance depends strongly on what is assumed about the genetic basis of the character. If the genetic variance of the character in each population is attributable to loci with numerous alleles of small effect that are in moderate frequency, as in Lande's (1975) model, the segregation variance should increase linearly with time since the populations were isolated, at a rate determined by the inverse of the effective population size. If the genetic variance is attributable to loci with alleles in very low frequency, as in Turelli's (1984) house-of-cards model or in Barton's (1990) model of pleiotropic, deleterious alleles, then the segregation variance in the hybrid population increases at a much lower rate.
Simulation of marker assisted selection for non-additive traits
Authors: Gimelfarb A. , Lande R.
Published: September 2009

Marker Assisted Selection (MAS) based on additive effects associated with alleles at marker loci, estimated by linear regression of individual phenotype on the markers, was applied to characters with non-additive gene action and non-additive environment. The base population was the F2generation of a cross between two inbred lines. Computer simulations of MAS were conducted for characters with dominance, epistasis and genotype-environment interaction approximated by the ‘additive-multiplicative’ model. MAS was more effective than purely phenotypic selection in all cases. The efficiency of MAS for characters with non-additive gene actionis comparable to (and for negative dominance even higher than) the efficiency of MAS for strictly additive characters. Environmental non-additivity, however, lowers the efficiency of MAS. Almost all results concerning the efficiency of MAS in our previoussimulations of purelyadditive traits are applicable to non-additive traits.
Decay of linkage disequilibrium in a finite island model
Authors: Tachida Hidenori
Published: September 2009

Time-dependent behaviour of linkage disequilibrium when there was initial linkage disequilibrium is studied in a finite island model assuming neutrality. Explicit expressions for linkage disequilibrium parameters are obtained. From these expressions, the initial and the ultimate decay rates of linkage disequilibrium parameters are found to be increased and decreased, respectively, by finiteness of the population when recombination rate, migration rate and inverse of subpopulation size are of comparable order. Thus, linkage disequilibrium created in the past may persist longerin smaller subdivided populations. Also, differentiation of the gametic parameter of linkage disequilibrium among subpopulations is found to diminish quickly compared tothe linkage disequilibrium in the whole population. Implications of these results for the interpretation of linkage disequilibria in natural populations are discussed.
The reduction in fixation probability caused by substitutions at linked loci
Authors: Barton N. H.
Published: September 2009

The probability of fixation of a mutation with selective advantageswill be reduced by substitutions at other loci. The effect of a single substitution, with selective advantage, can be approximated as a sudden reduction in the frequency of the favourable allele, by a fractionw= 1 −(s/S)r/s(whereris the recombination rate). An expression for the effect of a given sequence of such catastrophes is derived. This also applies to the ecological prxoblem of finding the probability that a small population will survive, despite occasional disasters. It is shown that if substitutions occur at a rate Δ, and are scattered randomly over a genetic map of lengthR, then an allele is unlikely to be fixed if its advantage is less than a critical value,Scrit= (π2/6)(2ΔS/(Rlog(S/s))). This threshold depends primarily on the variance in fitness per unit map length dueto substitutions, var(W)/R= 2ΔS/R. With no recombination, the fixation probability can be calculated for a finite population. If Δ >s, it is of the same order as for a neutral allele ( ≈ Δ/(2N(Δ−s))), whilst if, fixation probability is much higher than for a neutral allele, but much lower than in the absence of hitch-hiking. These results suggest that hitch-hiking may substantially impede the accumulation of weakly favoured adaptations.
The substructural organization of the chromosome core (scaffold) in meiotic chromosomes of Trilophidia annulata
Authors: Zhao Jian , Jin Shaobo , Hao Shui
Published: September 2009

The substructural organization of chromosome cores or nonhistone proteins was studied within intact metaphase chromosomes at the second meiotic division in the grasshopper Trilophidia annulata by silver staining as well as light microscopy and whole mount electron microscopy of squash chromosomes. Our results revealed that the metaphase II chromosome contains a longitudinal, helical coiling core structure. Probably the two last organizational levels of the core packaging are achieved by helical coiling. The core structure retains the morphological characteristics of the original metaphase chromosome, surrounded by a halo of dispersed materials, which may be composed mainly of nonhistone proteins. The kinetochore is found to be connected with the chromosome core. The present findings combined with our previous observations on the helical structure of metaphase II chromosomes suggest that the folding path of the internal core structure in metaphase chromosomes is consistent with the final helical arrangement of the chromosome itself. These observations also imply that in condensed metaphase chromosomes nonhistone protein may form a compact network structure with helical appearance, which extends throughout the entire chromosome.
Molecular analysis of opaque-2 alleles from Zea mays L. reveals the nature of mutational events and the presence of a hypervariable region in the 5′ part of the gene
Authors: Hartings Hans , Lazzaroni Nadia , Rossi Vincenzo , Riboldi Giorgia R. , Thompson Richard D. , Salamini Francesco , Motto Mario
Published: September 2009

Ten recessive Opaque-2 (O2) alleles of independent origin were characterized at the molecular level. The results revealed a high level of polymorphism at the O2 locus. In addition, our data suggest the possible cause for the recessive character of some of the alleles investigated, and allow us to infer some conclusions concerning the degree of relationship between the o2 mutations. Comparison of genomic sequences spanning the first exon and obtained from a series of wild-type and recessive alleles revealed the presence of a hypervariable region, involving different dipeptides, in the N-terminal part of the O2 protein.
Genotype-specific modifiers of transgene methylation and expression in the zebrafish,Danio rerio
Authors: Martin C. Cristofre , McGowan Ross
Published: September 2009

Previous reports involving mammalian systems, particularly mice, have demonstrated the existence ofcis- andtrans-acting modifiers of transgene methylation. These modifiers are thought to be important in dominance modification, genome imprinting and cellular expression mosaicism. Their potential role in the penetrance and severity of many complex human diseases could be of even greater significance. In the present investigation we demonstrate that modifiers that act in a similar fashion to those identified in mice also exist in a non-mammalian vertebrate, the zebrafishDanio rerio. We also provide evidence that the transgene methylation pattern may be influenced by the sex of the individual and environmental modulators such as temperature and sodium butyrate. These data support the theory that this type of dominance modification is mechanistically similar to position effect variegation inDrosophila. Furthermore, these data suggest evolutionary conservation of the modifiers, at least within vertebrates, and imply that they and their actions are important in normal vertebrate development.
A maternal genetic effect on the composition of mouse aggregation chimaeras
Authors: West John D. , Flockhart Jean H. , Kissenpfennig Adrien
Published: September 2009

Two series of 12½ day mouse chimaeric conceptuses were produced by aggregating (C57BL × CBA)F2strain preimplantation embryos with embryos that differed at theGpi-1slocus that encodes glucose phosphate isomerase, GPI-1. The composition of individual issues was evaluated by quantitative electrophoresis to estimate the % GPI-1A in the chimaeric tissue containing GPI-1A and GPI-1B. In one series of chimaeras, the GPI-1A cells were derived from a backcross between inbred BALB/c strain females and (BC × BALB/c)F1males, where BC is the partly congenic strain C57BL/Ola.AKR-Gpi-lsa,c/Ws. In the other series of chimaeras, the GPI-1A cells were derived from the reciprocal backcross between (BC × BALB/c)F1females and inbred BALB/c strain males. The [(BC × BALB/c)F1female × BALB/c male] ↔ (C57BL × CBA)F2series of chimaeras was reasonably balanced so that GPI-1 A and GPI-1B cells were fairly equally represented in the foetuses, placentas and extraembryonic membranes (tissue means: 37–51 % GPI-1A). This series did not differ significantly in composition from an earlier series of (BC × BALB/c)F2↔ (C57BL × CBA)F2chimaeras. However, the [BALB/c female × (BC × BALB/c)F1male] ↔ (C57BL × CBA)F2series of chimaeras was unbalanced, with mean tissue compositions (28–33% GPI-1A) that were intermediate between the above two balanced series and the unbalanced (BALB/c × BALB/c) ↔ (C57BL × CBA)F2series (tissue means: 14–22% GPI-1 A), that was studied previously. Thus, both (BALB/c×BALB/c) and [BALB/c×(BC x BALB/c)F1embryos contributed less to the tissues of chimaeric conceptuses than either (BC × BALB/c)F2or [(BC × BALB/c)F1× BALB/c] embryos. This implies that embryos from BALB/c mothers contributed less to the tissues of chimaeric conceptuses than embryos from (BC × BALB/c)F1mothers. We, therefore, conclude that a maternal genetic effect is responsible for some of the differences in composition among the four groups of chimaeras. This maternal effect must act before the 8-cell stage but it is not yet known whether it is mediated via cytoplasmic inheritance, genomic imprinting or by the reproductive tract. Evidence that a maternal effect retards preimplantation development of embryos from BALB/c females is reviewed and the possibility that this might cause them to contribute poorly to chimaeric conceptuses when aggregated with more precociously developing embryos is discussed.
Dynamics of polygenic variability under stabilizing selection, recombination, and drift
Authors: Gavrilets Sergey , Hasting Alan
Published: September 2009

We study the transient dynamics of the genotypic variance of an additive trait under stabilizing selection, recombination and random drift. We show how interaction of these factors determines the form and the rates of change of different components of the genotypic variance. LetVgbe the genie variance of the trait andCLbe the contribution of linkage disequilibrium to the genotypic variance. We demonstrate that the dynamics of the system on the plane (Vg,CL) are typically characterized by a quick approach to a straight line with slow evolution along this line afterwards. We show that the number of loci,n, and the population size,N, affect the expected dynamics ofVgmainly through the ratioN/n. We use our analytical and numerical results in interpreting the published results of artificial stabilizing selection experiments. The analysis suggests that it is drift and not selection that most likely led to the reduction of genetic variability in most of these experiments. Even very strong stabilizing selection only slowly removes polygenic variability from populations.
Linkage analysis of the gene encoding precursor protein of diapause hormone and pheromone biosynthesis-activating neuropeptide in the silkmoth, Bombyx mori
Authors: Pinyarat Waraporn , Shimada Toru , Xu Wei-Hua , Sato Yukihiro , Yamashita Okitsugu , Kobayashi Masahiko
Published: September 2009

We have determined the map position of the gene encoding a common precursor protein for diapause hormone and pheromone biosynthesis-activating neuropeptide (the DH-PBAN gene, Dh)in the silkmoth, Bombyx mori. First we compared the structure of introns in the DH-PBAN gene by the polymerase chain reaction, and found that the Dh locus carried three alleles, DhA1, DhA2 and DhB. The DhA1 and DhA2 alleles contained a fourth intron consisting of 740 bp, whereas DhB had a longer fourth intron of 770 bp. DhA1 and DhA2 contained a fifth intron consisting of 940 bp, whereas the fifth intron in DhB was much longer and consisted of 1700 bp. DhA1 was distinguished from DhA2 by an RFLP in the fifth intron after digestion with Rsa I. Linkage analyses using these polymorphisms showed that Dh was linked to the bp gene on chromosome 11, and independent of markers on chromosomes 1, 2, 3, 4, 5, 6, 7 and 13. To determine the map position, we obtained F1 hybrids between the n501 strain (K DhA1) and the w30 strain ( + KDhB), and backcrossed the F1 hybrid to females of the w30 strain. From the segregation of K and Dh in 864 individuals in the next generation, the recombination value was calculated as 25·5 % between K and Dh. Similarly we obtained backcross progeny between the No. 744 strain (BuDhA1) and the w30 strain ( + BuDhB), and calculated the recombination value between Bu and Dh as 30·4% from 487 progeny. Because k and Bu had already been mapped at positions 11–23·2 cM and 11–28·7 cM, respectively, we mapped Dh at 11--2·2 cM. The Dh locus is different from any loci which are known to control diapause, development or growth.
A general model for the evolution of recombination
Authors: Barton N. H.
Published: September 2009

A general representation of multilocus selection is extended to allow recombination to depend on genotype. The equations simplify if modifier alleles have small effects on recombination. The evolution of such modifiers only depends on how they alter recombination between the selected loci, and does not involve dominance in modifier effects. The net selection on modifiers can be found explicitly if epistasis is weak relative to recombination. This analysis shows that recombination can be favoured in two ways: because it impedes the response to epistasis which fluctuates in sign, or because it facilitates the response to directional selection. The first mechanism is implausible, because epistasis must change sign over periods of a few generations: faster or slower fluctuations favour reduced recombination. The second mechanism requires weak negative epistasis between favourable alleles, which may either be increasing, or held in check by mutation. The selection (si) on recombination modifiers depends on the reduction in additive variance of log (fitness) due to linkage disequilibria (υ1< 0), and on non-additive variance in log (fitness) (V′2,V′3,.. epistasis between 2, 3.. loci). For unlinked loci and pairwise epistasis,si= − (υ1+ 4V2/3)δr, where δris the average increase in recombination caused by the modifier. The approximations are checked against exact calculations for three loci, and against Charlesworth's analyses of mutation/selection balance (1990), and directional selection (1993). The analysis demonstrates a general relation between selection on recombination and observable components of fitness variation, which is open to experimental test.
Mating system, bottlenecks and genetic polymorphism in hermaphroditic animals
Authors: Jarne Philippe
Published: September 2009

A loss of neutral genetic polymorphism is theoretically expected for many reasons in inbreeding organisms when compared to outbreeders. The first reason derives from the decrease of the effective population size, down to a halving, in purely selfing species. Other genetical reasons include hitchhiking and background selection. A loss can also be caused by ecological processes, that is by any kind of process provoking a genetic bottleneck. These theoretical expectations have been empirically confirmed in hermaphroditic plants for which selfing species exhibit both a lower gene diversity and number of alleles per population. Here I extend the analysis to hermaphroditic animals, mainly terrestrial and freshwater snails. The decrease of variability in selfers is far greater than what is expected under the halving of the effective size of populations only. Hitchhiking and background selection certainly cannot be rejected as causes of this extra loss. Bottlenecks can clearly be invoked in tropical freshwater snails. However a crude theoretical analysis using Ewens's sampling formulae shows that the relative loss of variability estimated by the number of alleles is smaller in inbreeders than in outbreeders assuming populations with the same number of individuals. This suggests that bottlenecks contribute less to the loss in selfers than in outcrossers. Variability lost within selfing populations of hermaphroditic animals is also lost at the level of a group of populations (metapopulation). This is theoretically not always expected. Indeed, I calculate the ratio of the effective size of a selfing metapopulation to be greater than that of an outcrossing one using previously derived equations. The large variation of this ratio which depends on both migration and effective size of subpopulations prevents prediction of the relative amount of genetic variability stored by selfing and outcrossing metapopulations.
Mouse endogenous X-linked genes do not show lineage-specific delayed inactivation during development
Authors: Lebon Jeanne M. , Tam Patrick P. L. , Singer-Sam Judith , Riggs Arthur D. , Tan Seong-Seng
Published: September 2009

X chromosome inactivation (XCI) has been assumed to be complete in all cells of female mouse embryos at about 6 d post coitum (dpc). However, a recent study on β-galactosidase expression of an X-linkedlacZtransgene suggests that XCI is probably not complete several days after this time in some lineages. To help resolve this issue, we analysed XCI in embryos which carry the T(X;16)16H (Searle's) translocation and are heterozygous at the X-linkedHprtandPgk-1genes. The quantitative RT-PCR single nucleotide primer extension (SNuPE) assay was used to measureHprtandPgk-1allele-specific transcripts in embryos 9·5 dpc. No transcripts from the normal X chromosome were found in any of the tissues tested, indicating that inactivation was complete for these endogenous genes.
The unexpected recovery of hybrids in aDrosophilaspecies cross: a genetic analysis
Authors: Orr H. Allen
Published: September 2009

The species cross betweenDrosophila melanogasterandD. simulanswas first described by Sturtevant in the 1920s. According to his description, the hybridization ofD. simulans femalesandD. melanogastermales produces only (or almost only) male progeny. Female hybrids are embryonic lethal. Here it is shown that these traditional results no longer hold. Instead,D. simulansis polymorphic for factor(s) that qualitatively affect the outcome of species crosses toD. melanogaster. Remarkably, many, if not most, strains ofD. simulansproduce abundant female hybrids when crossed toD. melanogastermales. Genetic analysis of the difference betweenD. simulansstrains that produce many versus few hybrid females shows that recovery of hybrid females depends on autosomal, maternally acting gene(s).
Recombination load associated with selection for increased recombination
Authors: Charlesworth B. , Barton N. H.
Published: September 2009

Experiments 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

The 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

The 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

An 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

Equal 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

7-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

Currently 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

In 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

Thet-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

Using 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

Previous 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

Material 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

The 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

InDrosophila 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

This 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

We 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.
Background selection and patterns of genetic diversity inDrosophila melanogaster
Authors: Charlesworth Brian
Published: September 2009

Theoretical models of the effects of selection against deleterious mutations on variation at linked neutral sites (background selection) are used to predict the relations between chromosomal location and genetic variability at the DNA level, inDrosophila melanogaster. The sensitivity of the predictions to variation in the mutation, selection and recombination parameters on which they are based is examined. It is shown that many features of the observed relations between chromosomal location and level of genetic diversity inD. melanogastercan be explained by background selection, especially if the weak selective forces acting on transposable elements are taken into account. In particular, the gradient in diversity in the distal portion of the X chromosome, and the lack of diversity on chromosome 4 and at the bases of the major chromosomes, can be fully accounted for. There are, however, discrepancies between predicted and observed values for some loci inD. melanogaster, which may reflect the effects of forces other than background selection.
The effect of population size on effective population size: an empirical study in the red flour beetleTribolium castaneum
Authors: Pray Leslie A. , Goodnight Charles J. , Stevens Lori , Schwartz James M. , Yan Guiyun
Published: September 2009

Despite the increasing number of studies on the magnitude ofNe/Nratios, much remains unknown about the effects of demographic and environmental variables onNe/N. We determinedNe/Nfor seven population size treatments, ranging fromN= 2 toN= 960, in the red flour beetle Tribolium castaneum.Ne/Ndecreased with increasingN, as evidenced by a significant negative relationship between logNandNe/N. Our results are consistent with other published data on the relationship betweenNe/NandN. Effective population sizes in large populations may be much smaller than previously recognized. These results have important implications for conservation and evolutionary biology.