bluuebunny/crossref_metadata_2025_split huggingface dataset:
Do Eve's Alleles Live On?
Authors: Watterson G. A. , Donnelly P. 
Published: September 2009

SummaryConsider a random sample of genes at a locus, drawn from a population evolving according to the infinitely many, neutral, alleles model. The sample will have a most recent common ancestor gene, which we shall call ‘Eve’. The probability distribution, for the number of genes of oldest allelic type in a sample, is known and has a neat form. Rather less is known about the distribution for the number of genes in the sample which are of the same allelic type as Eve possessed. If the latter number is positive, then these genes are automatically of the oldest type in the sample. But Eve may have no non-mutant descendants in the sample; then, the oldest allele will be a mutant arising in a line of descent after Eve. The paper studies the number of non-mutant descendants from Eve, its distribution and moments. It seems that there may be few neat results. In large samples, the proportion of genes of Eve's type has an approximate β-like density, together with a discrete probability atom at zero, if the mutation rate parameter is low. Extinction of the allele of even the population's common ancestor is possible, but not certain, and bounds are obtained for its probability. Some comments are made about the applications and implications of the results for human mitochondrial DNA.
Mutation accumulation in finite outbreeding and inbreeding populations
Authors: Charlesworth D. , Morgan M. T. , Charlesworth B. 
Published: September 2009

SummaryWe have carried out an investigation of the effects of various parameters on the accumulation of deleterious mutant alleles in finite diploid populations. Two different processes contribute to mutation accumulation. In random-mating populations of very small size and with tight linkage, fixation of mutant alleles occurs at a high rate, but decreases with extremely tight linkage. With very restricted recombination, the numbers of low-frequency mutant alleles per genome in randommating populations increase over time independently of fixation (Muller's ratchet). Increased population size affects the ratchet less than the fixation process, and the decline in population fitness is dominated by the ratchet in populations of size greater than about 100, especially with high mutation rates. The effects of differences in the selection parameters (strength of selection, dominance coefficient), of multiplicative versus synergistic selection, and of different amounts of inbreeding, are complex, but can be interpreted in terms of opposing effects of selection on individual loci and associations between loci. Stronger selection slows the accumulation of mutations, though a faster decline in mean fitness sometimes results. Increasing dominance tends to have a similar effect to greater strength of selection. High inbreeding slows the ratchet, because the increased homozygous expression of mutant alleles in inbred populations has effects similar to stronger selection, and because with inbreeding there is a higher initial frequency of the least loaded class. Fixation of deleterious mutations is accelerated in highly inbred populations. Even with inbreeding, sexual populations larger than 100 will probably rarely experience mutation accumulation to the point that their survival is endangered because neither fixation nor the ratchet has effects of the magnitude seen in asexual populations. The effects of breeding system and rate of recombination on the rate of molecular evolution by the fixation of slightly deleterious alleles are discussed.
Meiotic drive on aberrant chromosome 1 in the mouse is determined by a linked distorter
Authors: Agulnik Sergei I. , Sabantsev Igor D. , Orlova Galina V. , Ruvinsky Anatoly O. 
Published: September 2009

SummaryAn aberrant chromosome 1 carrying an inverted fragment with two amplified DNA regions was isolated from wild populations ofMus musculus. Meiotic drive favouring the aberrant chromosome was demonstrated for heterozygous females. Its cause was preferential passage of aberrant chromosome 1 to the oocyte. Genetic analysis allowed us to identify a two-component system conditioning deviation from equal segregation of the homologues. The system consists of a postulated distorter and responder. The distorter is located on chromosome 1 distally to the responder, between thelnandPep-3genes, and it acts on the responder when intransposition. Polymorphism of the distorters was manifested as variation in their effect on meiotic drive level in the laboratory strain and mice from wild populations.
Effect of sperm genotype on chromatid segregation in female mice heterozygous for aberrant chromosome 1
Authors: Agulnik Sergei I. , Sabantsev Igor D. , Ruvinsky Anatoly O. 
Published: September 2009

SummaryAn aberrant chromosome 1 with two large homogeneously staining insertions was isolated from wild populations of Mus musculus musculus. The specific features of the aberrant chromosome have been described elsewhere (Agulnik et al. 1990). These include its preferential entry into the oocyte of heterozygous females, increased mortality of homozygotes and decreased fertility of homozygous females. Here we present data indicating that chromatid segregation in heterozygous females depends upon which sperm enters the oocyte before the second meiotic division: meioticdrive is powerful when it is sperm bearing normal chromosome 1, and segregation normalizesduring Mil when it is sperm bearing chromosome 1 with the extra segment. Experimental data are adduced and explanations offered for the observed phenomenon.
Group selection and the ‘shifting balance’
Authors: Rouhani S. , Barton N. H. 
Published: September 2009

SummaryWe investigate the establishment and spread of new adaptive peaks within Wright's ‘shifting balance’. The third phase of the ‘shifting balance’ involves a kind of group selection, since demes in which a superior peak has been established contain more individuals, and so send out more migrants. We assume that population size,N, increases with mean fitness,, according to the exponential relation,. Here,kis a measure of the weakness of density-dependent regulation, and equals the inverse of the regression of log (fitness) on log(N). In the island model, we find that just as with soft selection (k= 0), two distinct types of behaviour exist: group selection makes no qualitative difference. With low numbers of migrants, demes fluctuate almost independently, and only one equilibrium exists. With large numbers of migrants, all the demes evolve towards the same adaptive peak, and so the whole population can move towards one or other of the peaks. Group selection can be understood in terms of an effective mean fitness function. Its main consequence is to increase the effect of selection relative to drift (Ns), and so increase the bias towards the fitter peak. However, this increased bias depends on the ratio betweenkand the deme size (k/N), and so is very small when density-dependence is reasonably strong.
Evidence for aWolbachiasymbiont inDrosophila melanogaster
Authors: Holden Peter R. , Jones Peter , Brookfield John F. Y. 
Published: September 2009

SummaryThe bacterial cell division gene,ftsZ, was used as a specific probe to show the presence of a symbiotic bacterium in two wild type strains ofDrosophila melanogaster. Under stringent hybridization conditions we have shown that the bacterium is transferred to the progeny of these strains from infected mothers and can be eradicated by treatment with the antibiotic tetracycline. We have characterized this bacterium, by amplifying and sequencing its 16S rRNA gene, as being a member of the genus Wolbachia, an organism that is known to parasitize a range of insects includingDrosophila simulans. In a series of reciprocal crosses no evidence was found that the symbiont causes cytoplasmic incompatibility (CI) which is known to occur in infected strains ofD. simulans. The implications of these findings are discussed.
Parental origin of mutant allele does not explain absence of gene dose in X-linked Hyp mice
Authors: Qiu Z. Q. , Tenenhouse H. S. , Scriver C. R. 
Published: September 2009

SummaryThe expectation for a gene dose effect in an X-linked phenotype is that the corresponding metrical trait in heterozygous females will lie between values for affected hemizygous males and unaffected males and females. We made sequential measurements (at 30, 60, 90, 120 and 150 days) of serum phosphate concentration and tail length in mice with X-linked hypophosphatemia (genotypes: Hyp/Y, Hyp/+ and Hyp/Hyp) and in their normal litter-mates (genotypes: +/Y, +/+). We also measured renal mitochondrial 25-hydroxyvitamin D3-24-hydroxylase (24-hydroxylase) activity in 5 to 7-month-old mice fed control and low phosphate diets and representing all five genotypes. The animals were obtained by controlled breeding under uniform environmental conditions. The mutant animals all had uniformly and significantly lower serum phosphate levels, shorter tail length and higher 24-hydroxylase activity relative to unaffected litter-mates. There was no evidence of a gene dose effect because values were not significantly different among the three mutant genotypes. We also studied the influence of gamete of origin on serum phosphate, tail length and renal mitochondrial 24-hydroxylase activity in the Hyp/+ offspring of affected males (Hyp/Y) or affected females (Hyp/+ or Hyp/Hyp). We found no effect on the distribution of trait values. We conclude that parental origin of mutant allele does not explain the absence of a gene dose effect in Hyp mice.
Evolutionary effects of density-dependent selection in plants
Authors: Namkoong G. , Bishir J. , Roberds J. H. 
Published: September 2009

SummaryThe evolution of traits that affect genotypic responses to density regulated resources can be strongly affected by population dynamics in ways that are unpredictable from individual viability or reproduction potentials. Genotypes that are most efficient in utilizing energy may not always displace less efficient ones, and the evolution of energy allocation strategies may not always favour reproductive fitness because of their effects on destabilizing population growth rates. Furthermore, genetic polymorphisms in single loci that affect such traits can be maintained in populations with stable, periodic changes in population size and gene frequencies in the absence of heterozygote superiority. In fact, in the models investigated in this paper, the polymorphism is maintained, even in the absence of equilibrium genotypic frequencies.
Temperature related fertility selection on body size and the sex-ratio gene arrangement inDrosophila pseudoobscura
Authors: Gebhardt M. D. , Anderson W. W. 
Published: September 2009

SummaryWe measured temperature-dependent fertility selection on body size inDrosophila pseudoobscurain the laboratory. One hundred single females of each of the three karyotypes involving the ‘sexratio’ (SR) and the standard (ST) gene arrangement on the sex chromosome laid eggs at either 18 or 24°C. The experiment addressed the following hypotheses: (a) Fertility selection on body size is weaker at the higher temperature, explaining in part why genetically smaller flies appear to evolve in populations at warmer localities, (b) Homokaryotypic SR females are less fecund than homokaryotypic ST females, possibly mediated by the effect of body size on fertility, explaining the low frequencies of SR despite its strong advantage due to meiotic drive. The data were also expected to shed light on a mechanism for the evolution of plasticity of body size through fertility selection in environments with an unpredictable temperature regime. Hypothesis (a) was clearly refuted because phenotypically larger ST females had an even larger fertility surplus at the higher temperature and, more importantly, the genetic correlation between fertility and body size disappeared at the lower temperature. As to (b), we found that temperature affects fertility directly and indirectly through body size such that ST and SR females were about equally fecund at both temperatures, although different in size and size-adjusted fertility. We observed heterosis for both size and fertility, which might stabilize the polymorphism in nature. The reaction norms of body size to the temperature difference were steeper for ST females than for SR females, implying that fertility selection could change phenotypic plasticity of body size in a population. Selection on body size depended not only on the temperature, but also on the karyotypes, suggesting that models of phenotype evolution using purely phenotypic fitness functions may often be inadequate.
The mouse t complex distorter-3 (Tcd-3) locus and transmission ratio distortion
Authors: Silver Lee M. , Buck Christine 
Published: September 2009

SummaryA novel central partialthaplotype was generated by screening for a recombination event between overlapping distal and proximal partial haplotypes. This haplotype contains just two elementsTcrtandTcd-3t—involved in thet-specific transmission ratio distortion phenotype. Breeding analysis of males that carry this chromosome provides evidence thatTcd-3is, indeed, a distorter locus and not a second responder. Furthermore, the data indicate that a single well-defined distorter locus is insufficient to overcome completely the self-destructive, low transmission ratio distortion phenotype expressed by the t allele at the t complex responder locus, although a small, but highly significant, effect was observed.
Artificial sexual selection alters allometry in the stalk-eyed flyCyrtodiopsis dalmanni(Diptera: Diopsidae)
Authors: Wilkinson Gerald S. 
Published: September 2009

SummarySelection for increased and decreased ratio of eye span to body length was exerted on male stalk-eyed flies (Cyrtodiopsis dalmanni) from Malaysia using replicate selected and unselected lines. Response to selection was symmetrical. After 10 generations high line male eye span increased to 1·3 body lengths while low line male eye span declined to 1·1 body lengths. Realized heritabilities for eye span to body length ratio, estimated using regressions of deviations from unselected controls on cumulative selection differentials, were greater than zero for all four selected lines with averageh2= 0·35 + 0·06. The static linear allometric relationship between eye span and body length diverged between selected lines and rotated among selected line males in the same direction as among males in other sexually dimorphic diopsid species. Crosses between lines after 13 generations of selection indicate that the genes which influence relative eye span combine additively and do not exhibit sex linkage or maternal effects. The genetic correlation between the sexes, 0·29 + 0·05 as estimated by the regression of female on male change in eye span, did not prevent sexual dimorphism in eye span from diverging between lines. These results suggest that the exaggerated eye span of maleC. dalmanni is maintainedby natural selection opposing sexual selection rather than by lack of or asymmetry in additive genetic variation. Furthermore, the variation in sexual dimorphism for eye span-body length allometry observed among extant diopsid species is consistent with sexual selection of variable intensity acting on relative eye span.
Population dynamics of DNA fingerprint patterns within and between populations
Authors: Jin Li , Chakraborty Ranajit 
Published: September 2009

SummaryDNA fingerprint is a pattern of a variable number of bands (DNA fragments) with different sizes on a Southern gel for each individual, generated by one or many VNTR loci. Genetic divergence between individuals within and between populations can be studied in terms of number of shared bands between individuals. Using a population genetic model we show that the expectations of measures of genetic distance between populations based on band sharing data from DNA fingerprint patterns are functions of composite parametersM= 4Nv, and time of divergence (t) between populations, whereNis the effective size of the populations, and ν, the mutation rate. The expected genetic distance remains linear with time of divergence at least up toNgenerations as long as the average heterozygosity at the DNA fingerprint loci remains at or below 90%. Neither incomplete knowledge of the allele frequencies at each locus, nor the unknown number of loci underlying DNA fingerprint pattern, compromise these evolutionary dynamics of DNA fingerprint patterns. Applications of this theory to data on three human populations, and review of literature indicate that co-migration of alleles, and the presence of syntenic loci underlying the fingerprint pattern have little impact of the reliability of evolutionary conclusions from DNA fingerprint studies.
Genetic basis and evolution of species-specific courtship song in theDrosophila aurariacomplex
Authors: Tomaru Masatoshi , Oguma Yuzuru 
Published: September 2009

SummaryThe interpulse interval (IPI) of courtship song in theDrosophila aurariacomplex is the only parameter that is consistently species-specific among the several courtship elements examined within the complex. The genetic basis of the species-specific courtship song was examined by analysing the song of interspecific hybrids and of backcross progeny. IPI of all interspecific hybrids except two showed intermediate values, suggesting autosomal control of species-specific IPI. However, significant deviation for shorter IPI from midparent was found in thirteen out of 20 crosses. The chromosomal analysis betweenD. aurariaandD. biaurariarevealed that the two major autosomes had significantly large effects on IPI, but the sex chromosome and cytoplasm had no effect. Since no interaction was detected, it is concluded that each autosome acts additively in the determination of species-specific IPI. The common ancestors of theD. aurariacomplex may also have had autosomal control of IPI, which has been conserved during speciation in the complex.
Simulation of marker assisted selection in hybrid populations
Authors: Gimelfarb A. , Lande R. 
Published: September 2009

SummaryA computer model is developed that simulates Marker Assisted Selection (MAS) in a population produced by a cross between two inbred lines. Selection is based on an index that incorporates both phenotypic and molecular information. Molecular markers contributing to the index and their relative weights are determined by multiple regression of individual phenotype on the markers. The model is applied to investigate the efficiency of MAS as affected by several factors including total number of markers in the genome, number of markers contributing to the index, population size and heritability of the character. It is demonstrated that selection based on genetic markers can effectively utilize the linkage disequilibrium between genetic markers and QTLs created by crossing inbred lines. Selection is more efficient if markers contributing to the index are re-evaluated each generation than if they are evaluated only once. Increasing the total number of markers in the genome as well as the number of markers contributing to the index does not necessarily result in a higher efficiency of selection. Moreover, too many markers may result in a weaker response to selection. Population size is shown to be the most important factor affecting the efficiency of MAS.
Effects of autosomal inversions on meiotic exchange in distal and proximal regions of the X chromosome in a natural population ofDrosophila melanogaster
Authors: Sniegowski Paul D. , Pringle Anne , Hughes Kimberly A. 
Published: September 2009

SummaryWe have investigated the interchromosomal effect of the naturally-occurring paracentric inversionsIn(2L)tandIn(3R)Pon meiotic recombination in two regions of the X chromosome inDrosophila melanogaster. Previous authors have suggested that the rate of recombination at the tip of the X chromosome may be substantially higher in some natural populations than values measured in the laboratory, due to the interchromosomal effect of heterozygous autosomal inversions. This suggestion was motivated by observations that transposable elements are not as common at the tip of the X chromosome as predicted by recent research relating reduced meiotic exchange to increased element abundance inD. melanogaster. We examined the effects of heterozygousIn(2L)tandIn(3R)Pon recombination at both the tip and base of the X chromosome on a background of isogenic major chromosomes from a natural population. Both inversions substantially increased the rate of recombination at the base; neither one affected recombination at the tip. The results suggest that the presence of inversions in the study population does not elevate rates of crossing over at the tip of the X chromosome. The relevance of these results to ideas relating transposable element abundance to recombination rates is discussed.
Phenotypic conversion of mating type specificity induced by transplantation of macronucleoplasm inParamecium caudatum
Authors: Hori Manabu , Takahashi Mihoko 
Published: September 2009

SummaryAccording to the classical genetic analysis inParamecium caudatumby Tsukii & Hiwatashi (1983), the E mating type of each syngen is expressed when the cell bears alleles specific for syngen at theMtlocus. The O mating type is expressed when cells are homozygous for the null allele,mt, at theMtlocus. In suchmt/mtcells the O syngen specificity is determined by alleles at two other loci calledMAandMB. Inthe study reported here, macronucleoplasmic transplantation technique was used to test the above hypothesis. When macronucleoplasm of type E3(mating type E of syngen 3) was injected into a macronucleus of type O12(mating type O of syngen 12), some recipients changed to type E of the donor syngen but some others changed to type E of the recipient syngen. Thus, syngen specificity of donor macronucleoplasm controlling type E was converted into that of the recipients, even though the latter has no gene that controls type E. When this transformant expressing type E of the recipiexnt syngen was re-injected back into E of the other syngen, the expression of the converted mating type in some way continued in the recipient. This suggests that syngen specificity of geneMtof the donor was changed to that of the recipients by intersyngenic transplantation of macronucleoplasm. We also obtained results suggesting that the gene dosage ratio ofMttomtorMttoMAandMBmay be important for syngen specific expression of type E.
Mapping studies of the distal imprinting region of mouse Chromosome 2
Authors: Peters J. , Beechey C. V. , Ball S. T. , Evans E. P. 
Published: September 2009

SummaryThe known limits of the distal imprinting region of mouse Chromosome (Chr) 2 are defined by the breakpoints of the translocations T(2;8)2Wa, (T2Wa), and T(2;16)28H, (T28H), in distal H3, and proximal H4 respectively. We have shown that T2Wa and T(2;4)1Go, (T1Go), which has a breakpoint in central H3 map close toa, non-agouti.Ada, adenosine deaminase, lies very near the proximal boundary andRa, ragged, maps very close to the distal boundary, and is less than 0-2 cM from wasted,wst. From the current dataAdacan be taken as the proximal, andRaas the distal gene marker of the imprinting region on the linkage map. From consensus maps twenty three other markers, including fourteen genes, lie betweenAdaandRa, some of which may be useful in investigations of imprinting. Of the markers included in the study reported here, four,Ada,ls, lethal spotting,Raandwstlie or probably lie within the region but none display any evidence of imprinting. We suggest that recombination frequency is elevated in distal Chr 2, because in none of the crosses could the most closely linked marker be ordered in relation to the translocation breakpoint due to the high frequency of double crossovers.