bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evolution of the mitochondrial ATPase 6 gene in Drosophila: unusually high level of polymorphism in D. melanogaster
Authors: Kaneko Maki , Satta Yoko , Matsuura Etsuko T. , Chigusa Sadao I. 
Published: September 2009

SummaryWe have determined 1990 bp mitochondrial DNA sequence which extends from 3′ end of the cytochrome oxidase subunit I (COI) gene to 5′ end of the COIII gene from two sibling species of Drosophila, D. simulans and D. mauritiana. Analyses of the sequences and part of the NADH dehydrogenase subunit 2 gene and the COI gene together with those from D. melanogaster and D. yakuba revealed that amino-acid substitution rate of the ATPase 6 gene seems to be higher in some strains of D. melanogaster than in the other species. High level of amino-acid polymorphism in this gene was observed in D. melanogaster. Synonymous substitution rate is relatively constant in all the genes examined, suggesting that mutation rate is not higher in the ATPase 6 gene of D. melanogaster. The amino-acid substitutions found specifically in D. melanogaster are at the sites which are not conserved among mammals, yeast and E. coli. These sites of the ATPase 6 gene might lose the selective constraint in D. melanogaster, and the amino-acid substitutions can be explained by neutral mutations and random genetic drift.
Directional selection and the evolution of sex and recombination
Authors: Charlesworth Brian 
Published: September 2009

SummaryModels of the evolutionary advantages of sex and genetic recombination due to directional selection on a quantitative trait are analysed. The models assume that the trait is controlled by many additive genes. A nor-optimal selection function is used, in which the optimum either moves steadily in one direction, follows an autocorrelated linear Markov process or a random walk, or varies cyclically. The consequences for population mean fitness of a reduction in genetic variance, due to a shift from sexual to asexual reproduction are examined. It is shown that a large reduction in mean fitness can result from such a shift in the case of a steadily moving optimum, under light conditions. The conditions are much more stringent with a cyclical or randomly varying environment, especially if the autocorrelation for a random environment is small. The conditions for spread of a rare modifier affecting the rate of genetic recombination are also examined, and the strength of selection on such a modifier determined. Again, the case of a steadily moving optimum is most favourable for the evolution of increased recombination. The selection pressure on a recombination modifier when a trait is subject to strong truncation selection is calculated, and shown to be large enough to account for observed increases in recombination associated with artificial selection. Theoretical and empirical evidence relevant to evaluating the importance of this model for the evolution of sex and recombination is discussed.
The genetics of the Luria–Latarjet effect in bacteriophage T4: evidence for the involvement of multiple DNA repair pathways
Authors: Hyman Paul 
Published: September 2009

SummaryThe Luria-Latarjet effect is an increase in resistance of a virus to DNA damage during infection of a host. It has often been assumed to involve recombinational repair, but this has never been demonstrated experimentally. Using nine bacteriophage (phage) T4 mutants, I present evidence indicating that, for phage T4, the Luria-Latarjet effect is due to three repair pathways-excision repair, post-replication-recombinational-repair (PRRR) and multiplicity reactivation (MR) (a second form of recombinational repair). The results also show that the Luria-Latarjet effect develops in two stages. The first stage starts soon after infection. Damage which occurs during the first stage can be repaired by excision repair or PRRR. The second stage appears to start after the first round of DNA replication is complete. DNA damage which occurs during this stage can apparently be repaired by MR as well as the other two repair pathways. The results of this study support the hypothesis that recombinational repair has been selected to ensure that the progeny phage genomes which are packaged have minimum DNA damage. Since other viruses which infect bacterial, animal and plant cells show a Luria-Latarjet effect similar to that in phage T4, the conclusions from this study may have wide applicability.
Correction of chlorophyll deficiency in alloplasmic male sterileBrassica junceathrough recombination between chloroplast genomes
Authors: Kirti P. B. , Narasimhulu S. B. , Mohapatra T. , Prakash S. , Chopra V. L. 
Published: September 2009

SummaryBrassica junceacv. Pusa Bold carryingB. oxyrrhinacytoplasm (oxycytoplasm) was male sterile and chlorotic under field conditions at low temperature (Prakash & Chopra, 1990). Leaf protoplasts of the chlorotic male sterile alloplasmic line (2n = 36) were fused with hypocotyl protoplasts of green male fertile,B. junceacv. RLM-198 (2n = 36) using polyethylene glycol. Of the 1043 plants regenerated from 10 fusion experiments, 123 had ‘gigas’ features and were identified as presumptive fusion products. Among field-grown population, one plant was dark green even at low temperatures and male sterile. It possessed 72 chromosomes which formed 36 bivalents at late diakinesis of meiosis-I. This plant was back-crossed toB. junceacv. Pusa Bold (the maintainer line) for three successive generations. One male sterile, normal green BC3 progeny plant with 2n = 36 was analyzed for organelle constitution. Probing its total DNA with the mitochondrial gene for cytochrome oxidase subunit I revealed that it possessed mitochondria ofB. oxyrrhina. Southern hybridization pattern with the gene for ribulose bisphosphate carboxylase oxygenase-large subunit (rbcL) revealed that the chloroplast genome of the chlorophyll deficiencycorrected plant had characteristics of bothB. junceaandB. oxyrrhina. The deficiency correction has been attributed to recombination between chloroplast genomes of the two species.
Dosage dependent modifiers ofwhitealleles inDrosophila melanogaster
Authors: Sabl Joy F. , Birchler James A. 
Published: September 2009

SummaryAs part of a study to identify dosage-sensitive modifiers of thewhiteeye colour locus and the retrotransposon, copia, a segmental aneuploid screen was conducted. It surveys the autosomal complement of the genome for dosage dependent modifiers ofwhite, including ones effective upon retrotransposon insertion-induced alleles. Several regions were found which, when present as a segmental trisomy, affected one or more of the alleles tested in a strong and consistent fashion. Two of these regions have been identified as containing previously described modifiers,Darkener of-apricotandInverse regulator-a. The remainder identify newwhiteallele modifiers. Selected segmental monosomics were also tested where possible for regions exhibiting a trisomic effect. At least three regions were found to have a dosage-dependent effect in one, two and three copies.
Heritabilities of growth curve parameters and age-specific expression of genetic variation under two different feeding regimes in Japanese quail (Coturnix coturnix japonica)
Authors: Gebhardt-Henrich Sabine G. , Marks Henry L. 
Published: September 2009

SummaryThis study investigated genetic variation in growth and final size in relationship to differences in heritabilities under good and poor feeding conditions. Heritabilities of growth and final size were estimated for several traits underad libitumand restricted feeding conditions. A 30% feed restriction from hatching to 44 days of age in Japanese quail chicks decreased body weight and tarsus length at 44 days of age and the length of the third primary covert feather at 24 days of age relative to controls fedad libitum. Wing length at 44 days of age was not significantly different forad libitumfed and restricted quail. Genetic variances for body weight and tarsus length were very large throughout growth which resulted in heritability estimates close to one for these traits. The genetic correlations among feeding treatments were low, indicating that different genes were affecting growth under the two treatments. Growth was described by the components: asymptote, growth period, and shape of the growth curve following the modified Richards growth curve model (Brisbinet al.1986). Tarsus length, which had high heritability of the parameter ‘growth period’ of the model, tended to display a higher heritability under the restriction than underad libitumfeeding. Body weight and feather length, which had either no heritable or low heritable ‘growth periods’ estimates, tended to be more heritable underad libitumfeeding. The shape parameter of the growth curve was not heritable for any trait, except tarsus length under restricted feeding.
Do self-fertilization and genetic drift promote a very low genetic variability in the allotetraploidBulinus truncatus(Gastropoda: Planorbidae) populations?
Authors: Njiokou Flobert , Bellec Christian , Berrebi Patrick , Delay Bernard , Jarne Philippe 
Published: September 2009

SummaryBulinus truncatus, one of the intermediate hosts of the genusSchistosomais an hermaphrodite freshwater snail species occupying a variety of environments over almost all Africa. These environments are subjected to large variations in water availability.B. truncatusis allotetraploid and its populations exhibit various frequencies of aphallic individuals (unable to reproduce as male). Both traits probably favour a reproduction by self-fertilization. Here we investigate the genetic structure of populations ofB. truncatusof Niger and Ivory Coast using protein electrophoresis to analyse the influence of the environment and of both the last traits. To obtain an estimate of the true heterozygosity in this allotetraploid species, we analyse independently the two diploid loci at each tetraploid locus. Our study indicates (i) an extremely low intrapopulation polymorphism with most alleles fixed and the total absence of heterozygotes and (ii) low differentiation between populations. These results indicate high gene flow between populations. However, the existence of private alleles sometimes at high frequency, the low polymorphism and the lack of heterozygotes point to the role of both genetic drift and self-fertilization, the second amplifying the genetic consequences of the first.
The use of retrotransposons as markers for mapping genes responsible for fitness differences between relatedDrosophila melanogasterstrains
Authors: Nuzhdin Sergey V. , Keightley Peter D. , Pasyukova Elena G. 
Published: September 2009

SummaryHitch-hiking of dispersed mobile elements serving as molecular markers was used as a new tool for mapping quantitative trait loci inDrosophila melanogaster. TwoDrosophilastrains with high fitness (HA) were backcrossed repeatedly to a closely related strain with low fitness (LA) to initiate experimental populations with expected HA gene frequencies of 1/32. The frequencies of 19 insertion sites of the retrotransposonsmdg1andcopiawere analyzed after 11 to 17 generations. Frequencies of sites from the HA line increased substantially in the pericentromeric region, indicating that one or more loci responsible for the fitness difference between the strains were located there. A maximum likelihood (ML) procedure was applied to estimate selection coefficients associated with the markers, and this indicated a broad, strongly selected region of the chromosome. At least one additional locus was localized in the middle of the 2L arm. Possible applications of this method are discussed.
The probability of fixation of a favoured allele in a subdivided population
Authors: Barton N. H. 
Published: September 2009

SummaryIn a stably subdivided population with symmetric migration, the chance that a favoured allele will be fixed is independent of population structure. However, random extinction introduces an extra component of sampling drift, and reduces the probability of fixation. In this paper, the fixation probability is calculated using the diffusion approximation; comparison with exact solution of the discrete model shows this to be accurate. The key parameters are the rates of selection, migration and extinction, scaled relative to population size (S = 4Ns, M = 4Nm, Λ = 4Nλ); results apply to a haploid model, or to diploids with additive selection. If new colonies derive from many demes, the fixation probability cannot be reduced by more than half. However, if colonies are initially homogeneous, fixation probability can be much reduced. In the limit of low migration and extinction rates (M, Λ ≪ 1), it is 2s/{1 + (Λ/MS)(1 −exp(−S))}, whilst in the opposite limit (S≪ 1), it is 4sM/{Λ(Λ +M)}. In the limit of weak selection (M, Λ ≫ 1), it is 4sM/{Λ(Λ +M)}. These factors are not the same as the reduction in effective population size (Ne/N), showing that the effects of population structure on selected alleles cannot be understood from the behaviour of neutral markers.
Inheritance of a meiotic abnormality that causes the ovulation of primary oocytes and the production of digynic triploid mice
Authors: West John D. , Webb Sheila , Kaufman Matthew H. 
Published: September 2009

SummaryPrevious studies have demonstrated that the LT/SvKau strain of mice ovulates a high proportion of oocytes as diploid primary oocytes rather than secondary oocytes. These ovulated primary oocytes are arrested at meiotic metaphase I but may be fertilized to produce digynic triploid embryos. In the present study, 40·4% of eggs analysed from LT/SvKau females were ovulated as primary oocytes, compared to 1·2% from control C57BL/Ws strain mothers. These two inbred strains were intercrossed to produce eight sets of Fl, F2 and backcross females and the frequency of triploidy was investigated. The results are compatible with segregation of a co-dominant, autosomal gene that has a major influence on the incidence of triploidy. We suggest that the provisional gene symbolPoo(primary oocyte ovulation) be assigned to this gene, with allelesPool(the ‘mutant’ allele present in the LT/SvKau strain) andPoob(the normal allele present in C57BL/Ws mice).Poois incompletely penetrant and has variable expressivity because the proportion of oocytes ovulated as primary oocytes by LT/SvKau mice was variable and, in some cases, nil. In putativePool/Poobheterozygotes the frequency of ovulated primary oocytes was increased only marginally (from 1·2% to 66%) by the presence of one copy of thePoolallele, but this increase was found consistently (in two reciprocal Fl crosses) and was statistically significant. No evidence was found for tight genetic linkage betweenPooand two Mendelian loci (brown on chromosome 4 and glucose phosphate isomerase on chromosome 7), that were segregating in the crosses. ThePoolmutant in the LT/SvKau strain of mice provides a valuable resource to study the cell and molecular biology of mammalian oocyte maturation and the control of meiosis.
Detection of quantitative trait loci from frequency changes of marker alleles under selection
Authors: Keightley Peter D. , Bulfield Grahame 
Published: September 2009

SummaryA method was developed to estimate effects of quantitative trait loci (QTL) by maximum likelihood using information from changes of gene frequency at marker loci under selection, assuming an additive model of complete linkage between markers and QTL. The method was applied to data from 16 molecular and coat colour marker loci in mouse lines derived from the F2of two inbred strains which were divergently selected on 6-week weight for 21 generations. In 4 regions of the genome, marker allele frequencies were more extreme than could be explained by sampling, implying selection at nearby QTL. An effect of about 0·5 standard deviations was located on chromosome 11, and accounted for nearly 10% of the genetic variance in the base population. QTL with effects as small as 0·2 phenotypic standard deviations could be detected. For typing of a given number of individuals, the power of detection of QTL is very high compared to, for example, analysis of an F2 population. The joint effects of linkage and selection were investigated by Monte Carlo simulation. Marker gene frequencies change little as a consequence of selection at a QTL unless the marker and QTL are less than about 20 cM apart.
Prediction of long-term contributions and inbreeding in populations undergoing mass selection
Authors: Woolliams J. A. , Wray N. R. , Thompson R. 
Published: September 2009

SummaryFor a population undergoing mass selection, derived from an unselected base population in generation zero, the expected long-term contribution to the population of an ancestor from generation 1 was shown to be equal to that expected during random selection multiplied by(whereis one half the breeding value of the ancestor for the trait under selection standardized by the phenotypic standard deviation,ithe intensity of selection, andis the competitiveness which is defined bythe heritability in generation 2 andkthe variance reduction coefficient). It was shown that the rate of inbreeding (ΔF) could be partitioned into three components arising from expected contributions, sampling errors and sampling covariances respectively. Using this result ΔFwas derived and shown to be dominated by terms that describe ΔFby variance of family size in a single generation plus a term that accounts for the expected proliferation of lines over generations from superior ancestors in generation 1. The basic prediction of ΔFwas given bywhereMandFare the numbers of breeding males and females,Tthe number of offspring of each sex,ρmand ρtare correlations among half-sibs in generation 2 for males and females respectively, andKis a function of the intensity and competitiveness.
Differences inPelement population dynamics between the sibling speciesDrosophila melanogasterandDrosophila simulans
Authors: Kimura Kiyoshi , Kidwell Margaret G. 
Published: September 2009

SummaryPatterns ofPelement establishment and evolution were compared in populations of D.melanogasterand D.simulans. For each species, mixed populations were initiated withMstrain flies lackingPelements together withPstrain flies having similarPelement copy numbers and phenotypes. The mixed populations were subsequently maintained under similar environmental conditions. On the basis of gonadal sterility assays,Pelements tended to be significantly more active inD.melanogasterthan inD.simulanspopulations. This activity difference between the two species was positively associated withPelement copy number, determined by restriction enzyme analysis, and transposition frequency, as determined by a transposition assay. Host factors are the most likely explanation for the observed species variation. Difficulty of establishment may be a factor determining the absence ofPelements in natural populations ofD.simulans.
Sources of information for estimating heritability from selection experiments
Authors: Thompson R. , Atkins K. D. 
Published: September 2009

SummaryMaximum likelihood estimation methods with an individual animal model were used to analyse a bi-directional selection experiment, with control, for cannon bone length in Scottish Blackface sheep. A method is described for partitioning the likelihood to allow within- and between-line estimates of genetic variance. It is concluded that both sources of information made substantial contributions to the precision of the base population heritability estimate. The implications for different experimental designs and varying heritability are discussed.
Error thresholds and stationary mutant distributions in multi-locus diploid genetics models
Authors: Higgs Paul G. 
Published: September 2009

SummaryWe study multi-locus models for the accumulation of disadvantagenous mutant alleles in diploid populations. The theory used is closely related to the quasi-species theory of molecular evolution. The stationary mutant distribution may either be localized close to a peak in the fitness landscape or delocalized throughout sequence space. In some cases there is a sharp transition between these two cases known as an error threshold. We study a multiplicative fitness landscape where the fitness of an individual withjhomozygous mutant loci andkheterozygous loci iswjk= (1 −s)j(1 −hs)k. For a sexual population in this landscape there are two types of solution separated by an error threshold. For a parthenogenetic population there may be three types of solution and two error thresholds for some values ofh. For a population reproducing by selfing the solution is independent ofh, since the frequency of heterozygous individuals is negligible. The mean fitnesses of the populations depend on the reproductive method even for the multiplicative landscape. The sexual may have a higher or lower fitness than the parthenogen, depending on the values ofhandu/s. Selfing leads to a higher mean fitness than either sexual reproduction or parthenogenesis. We also study a fitness landscape with epistatic interactions withwjk= exp(−s(2j+k)α). The sexual population has a higher fitness than the parthenogen when α > 1. This confirms previous theories that sexual reproduction is advantageous in cases of synergistic epistasis. The mean fitness of a selfing population was found to be higher than both the sexual and the parthenogen over the range of parameter values studied. We discuss these results in relation to the theory of the evolution of sex. The fitness of the stationary distribution in cases where unfavourable mutations accumulation is one factor which could explain the observed prevalence of sexual reproduction in natural populations, although other factors may be more important in many cases.
Evolution ofCastanea sativaMill, in Turkey and Europe
Authors: Villani F. , Pigliucci M. , Cherubini M. 
Published: September 2009

SummaryThe evolution of sweet chestnut (Castanea sativaMill.) appears to be a complex mixture of long-range gene flow, natural and artificial selection, and local effects of isolation by distance. In this paper we present the most complete analysis to date on the genetic structure and variability of 52 populations of chestnut spanning the entire European area of distribution. The study is based on the use of isozyme data. Our samples came from four major zones, possibly representing relevant steps in the evolution and spread of sweet chestnut in Europe: (i) eastern Turkey, the supposed center of origin of the species; (ii) western Turkey, the area in which human domestication started; (iii) Italy, where domesticated chestnut was first introduced to the rest of Europe by the Romans; and (iv) France, representing the latest phases of the expansion, close to the northern limit of the taxon.As previous studies based only on Italian and some Turkish populations suggested, the electrophoretic data are consistent with a series of episodes of west- and north-ward migration. The early expansion from the center of origin was probably slow, resulting from natural diffusion of the species. Most of the original genetic variation has been conserved during this phase. Successive episodes of colonization of western Turkey and then of the rest of Europe were probably the more rapid result of human activity. These later stages were associated with genetic drift that reduced the overall heterozygosity of the extant populations. No evidence for selection could be found at the large geographical scale of this study, although previous regional works have shown spatial patterns of allelic frequencies at a few loci and phenotypic differentiation consistent with the action of past selective pressures.