bluuebunny/crossref_metadata_2025_split 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

SummaryTo 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

SummaryIn 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

SummaryWe 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

SummaryMarker 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

SummaryTime-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

SummaryThe 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

SummaryThe 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

SummaryTen 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

SummaryPrevious 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

SummaryTwo 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

SummaryWe 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

SummaryWe 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

SummaryA 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

SummaryA 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

SummaryX 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

SummaryThe 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).