bluuebunny/crossref_metadata_2025_split huggingface dataset:
Genome size variation in the North American sunfish genusLepomis(Pisces: Centrarchidae)
Authors: Ragland Chara J. , Gold John R. 
Published: September 2009

SummaryGenome sizes (nuclear DNA contents) were documented spectrophotometrically from individuals of each of nine species of the North American centrarchid (sunfish) genusLepomis. The distributions of DNA values within and among the nine species were essentially normal and continuous, suggesting that changes in DNA quantity inLepomisare small in amount, involve both gains and losses of DNA, and are cumulative and independent in effect. Significant differences in mean genome size were found between individuals within populations in all nine species and between species. Nested analysis of variance and comparisons of average genome size difference or distance between individuals drawn from different levels of taxonomic organization revealed that the majority of genome size divergence inLepomisoccurs above the hierarchical level of individuals within populations. TheLepomisdata when compared to similar data from North American cyprinid fishes appear to suggest that: (i) genome size evolution in these fishes at least follows a continuous rather than a discontinuous mode; (ii) the general predictions of hypothetical models relating genome size variation as a function of organismal position along adaptive continua may be oversimplified, or not applicable to complex, higher eukaryotes; and (iii) changes in genome size in these fishes may be concentrated in speciation episodes.
X-inactivation of theStslocus in the mouse: an anomaly of the dosage compensation mechanism
Authors: Jones Janet , Peters Josephine , Rasberry Carol , Cattanach Bruce M. 
Published: September 2009

SummaryThe behaviour of theX- andY-borneStslocus has been studied in male and female mice. There was considerable heterogeneity in STS activity between inbred mouse strains, with a four fold difference in activity between the highest (101/H) and lowest (Ju/Ct) activity strains, which can be interpreted in terms of allelic differences. In all inbred strains male STS levels were higher than those of female STS levels and in the majority of strains tested male STS levels were nearly twice as high as female levels. Reciprocal crosses between C3H/HeH and the STS-deficient substrain, C3H/An, demonstrated that activities of theX- andY-borne genes in males are essentially the same and this suggested that the lower STS level in females derives fromX-inactivation of the locus. The possibility that hormonal differences could instead be responsible for the lower activity in females was ruled out by the findings that (a) castration of males did not reduce their STS levels and (b) sex-reversed males,X/X Sxr, had STS levels typical of females. Final proof that the mouseStslocus can be subject to theX-inactivation process was provided by the observation thatXXfemales had STS levels that were only slightly (20%) higher than those ofXOfemales. The difference may indicate incomplete inactivation of the locus. Linkage data verifying the location ofStson the distal end of theXchromosome are provided.In total, the results of this study show that the murineStslocus can be subject to theX-inactivation process and this, together with the existence of functional loci of near-equal activities on theXandYchromosomes, results in an imbalance of STS levels between the sexes.X-inactivation does not therefore serve as a dosage compensation mechanism for theStslocus in the mouse. All of these findings were made in C3H/HeH mice or in animals carrying C3H/HeH functionalStsalleles, and it is pointed out that the diverse results previously obtained by other investigators may be attributable to their use of different strains and crosses between strains but could also be complicated by technical factors.
Age differences between distributions of genotypes among pregnant women: evidence of fertility selection
Authors: Gimelfarb A. , Bottini E. 
Published: September 2009

SummaryThe number of children produced by a modern woman is usually below her total reproductive capacity and is determined by circumstances other than natural selection. It is, therefore, practically impossible to detect differences in natural fertilities associated with different types (e.g. phenotypes, genotypes) of women. This does not mean, however, that natural selection at the reproductive level cannot at all be detected today. If women of a particular type have high natural fertility, this usually means that they reproduce (become pregnant) at a higher rate than women of a type with lower natural fertility. Hence, when there is a limit on the number of children, women of the first type will reach the limit at an earlier age than women of the second type. As a result, types that have a higher natural fertility should be overrepresented among pregnant women of younger ages and, consequently, underrepresented among older ones, as compared to types with a lower natural fertility. Based on this notion, a model of age-related differences between distributions of types among pregnant women is suggested. The model is applied to data on MNSs-blood group and PGM1 (phosphoglucomutase) types in a sample of pregnant women and an evidence of natural selection at the reproduction level associated with these genetic markers is obtained.
The divergence of a polygenic system subject to stabilizing selection, mutation and drift
Authors: Barton Nick 
Published: September 2009

SummaryPolygenic variation can be maintained by a balance between mutation and stabilizing selection. When the alleles responsible for variation are rare, many classes of equilibria may be stable. The rate at which drift causes shifts between equilibria is investigated by integrating the gene frequency distributionW̅2NΠ(pq)4Nμ−1. This integral can be found exactly, by numerical integration, or can be approximated by assuming that the full distribution of allele frequencies is approximately Gaussian. These methods are checked against simulations. Over a wide range of population sizes, drift will keep the population near an equilibrium which minimizes the genetic variance and the deviation from the selective optimum. Shifts between equilibria in this class occur at an appreciable rate if the product of population size and selection on each locus is small (Nsα2< 10). The Gaussian approximation is accurate even when the underlying distribution is strongly skewed. Reproductive isolation evolves as populations shift to new combinations of alleles: however, this process is slow, approaching the neutral rate (≈ μ) in small populations.
Somatic reversion of P transposable element insertion mutations in thesingedlocus ofDrosophila melanogasterrequiring specific P insertions and atrans- acting factor
Authors: Brookfield John F. Y. , Lewis Alan P. 
Published: September 2009

SummaryDestabilization in somatic cells of P-element insertions in the X-linkedsingedgene ofDrosophila melanogasterhas been studied. We have shown that some but not all unstable P-element insertions insingedcan form mosaics. The cause of this variation is not clear from studies of the restriction maps of the mutations tested. The transposable element movements occur early in development and require, in addition to an appropriate P-element insertion insinged, atrans-acting maternal effect component. Movements appear to occur preferentially in attached-X stocks. However, the maternal effect component maps to the central region of chromosome 2.
The occurrence of long ribosomal transcripts homologous to type I insertions in bobbed mutants ofDrosophila melanogaster
Authors: Makni Mohamed , Marrakchi Mohamed , Prud'Homme Nicole 
Published: September 2009

SummaryInDrosophila melanogasterup to two thirds of the rDNA genes contain insertion sequences of two types in the 28S coding region. Comparison of the ribosomal insertion transcripts in the wild type and in two bobbed mutants reared at two temperatures showed that the level of type I transcripts is dependent on both the number of genes with type I insertions in the bobbed loci and the intensity of bobbed phenotype. Importantly, a long transcript of 8·7 kb hybridized to the ribosomal probe, the INS I probe and also to the restriction fragment of the rDNA downstream of the point of insertion was found in one bobbed mutant. This result and also those from sandwich hybridization indicate that some interrupted ribosomal genes are functional.
Restriction map and α-amylase activity variation amongDrosophilamutation accumulation lines
Authors: Tachida H. , Harada K. , Langley C. H. , Aquadro C. F. , Yamazaki T. , Cockerham C. C. , Mukai T. 
Published: September 2009

SummaryThe specific activities of α-amylase were measured for two sets of mutation accumulation lines, each set having originated from a different lethal-carrying second chromosome andSM1(Cy) chromosome and having been maintained by a balanced lethal system for about 300 generations. Significant variation was found to have accumulated among lines of both sets. Because of dysgenic crosses in the early generations of mutation accumulation, insertions or deletions of transposable elements in theAmygene region were suspected of being the cause of this variation. In order to test this possibility, the structural changes in the 14 kb region of these chromosomes that includes the structural genes for α-amylase were investigated by restriction map analysis. We found that most part of the activity variation is due to replacements of a chromosomal region ofSM1(Cy), including the structural genes for α-amylase, by the corresponding regions of the lethal chromosomes. One line also contained an insertion in this region but this line has an intermediate activity value. Thus, insertions of transposable elements into theAmygene region were not found to be responsible for the new variation observed in α-amylase activity. If we remove those lines with structural changes from the analysis, the genetic variance of α-amylase specific activity among lines becomes non-significant in both sets of chromosomes.
Paternal inheritance of egg traits in mice: a case of genomic imprinting
Authors: Bander S. A. A. , Watson S. C. , Shire J. G. M. 
Published: September 2009

SummaryEggs from reciprocal hybrids between the C57BL/6By and BALB/cBy strains were tested for their susceptibility to attack by hyaluronidase and pronase. There were significant reciprocal differences between the F1females in the responses of their unfertilized eggs to both enzymes. The F1hybrids from BALB mothers showed the increased susceptibility characteristic of C57BL whilst the F1hybrids with C57BL mothers were more resistant to both enzymes, like BALB mice. Eggs from the four kinds of reciprocal F2hybrid females also showed patroclinous patterns of susceptibility. A patroclinous difference was found between reciprocal crosses of the CXBD and CXBE recombinant inbred strains but not in crosses between recombinant inbred strains with similar phenotypes. Cross fostering did not alter the phenotypes of the C57BL and BALB females or those of their reciprocal F1hybrids. The findings are interpreted in terms of differential genomic imprinting of paternally inherited information. The possible general usefulness of patroclinous differences between reciprocal F1females in revealing differences in imprinting is noted.
Relative growth of the skull and postcranium in giant transgenic mice
Authors: Shea Brian T. , Hammer Robert E. , Brinster Ralph L. , Ravosa Matthew R. 
Published: September 2009

SummaryCross-sectional allometric growth patterns of the cranial and postcranial skeleton were compared between giant transgenic (MT-rGH) mice and their normal littermate controls. Body weights, external body dimensions, and a series of cranial and postcranial linear dimensions of the skeleton were determined for samples of known age. Comparative bivariate and multivariate allometric analyses were completed in order to determine whether (1) the larger transgenic mice differed significantly from the normal controls in aspects of body and skeletal proportions, and (2) any such proportion differences resulted from general allometric effects of overall weight or skeletal size increase. Results demonstrate that the transgenic mice do exhibit significantly different body and skeletal proportions than normal control adults. Allometric comparisons of the skeletal dimensions relative to body weight reveal similar coefficients of growth allometry but several differences iny-intercept values in the transgenicvs.control groups. The comparisons among the skeletal dimensions of the skull and postcranium generally reveal the sharing and differential extension of common growth allometries in the two groups. Thus, the elevated levels of growth hormone (GH) and insulin-like growth factor I (IGF-I) in the transgenic mice appear to result in increased overall growth for the various skeletal elements, but in the relative proportions determined by intrinsic growth controls within that system.
Tissue specific effects of ommochrome pathway mutations inDrosophila melanogaster
Authors: Tearle Rick 
Published: September 2009

SummaryThe tissue-specific effects of 17 mutations affecting the synthesis of brown eye pigment (xanthommatin) have been investigated by combining them withchocolateandred cells, two mutations causing ectopic pigmentation of the Malpighian tubules and larval fat body (which normally only synthesize pigment precursors). The majority of mutations block the pigmentation of four organs: the normally pigmented eyes and ocelli, and ectopically pigmented tubules and fat body. They represent genes that would appear to be required for the normal operation of the pathwayper seand are likely to encode structural proteins. Mutations at 5 loci affect pigmentation of a subset of organs:cdandpoaffect only the eyes and ocelli;karaffects the eyes, ocelli and fat body;carcauses excretion of pigment from tubules; and z affects pigmentation of the eyes alone. Of these loci, only z has been shown to encode a regulatory protein and the role of the remaining four gene products is not clear. Two mutations affecting the red eye pigments (drosopterins),bwandmal, do not substantially perturb brown pigment synthesis in any of the four organs.
Analysis of lines of mice selected for fat content: 3. Flux through thede novolipid synthesis pathway
Authors: Asante Emmanuel A. , Hill William G. , Bulfield Grahame 
Published: September 2009

SummaryThe flux through thede novofatty acid synthesis pathway was estimated in lines of mice which differed substantially in fat content following 26 generations of selection at 10 weeks of age. Previous estimates of lipogenic enzyme activities had indicated an increase in the capacity for lipogenesis in the Fat compared to the Lean line. Therefore thein vivoflux in lipogenesis was measured in both liver and gonadal fat pad (GFP) tissues of males at 5 and 10 weeks of age, using the rat of incorporation of3H from3H2O and14C from acetate and citra te into total lipids. AT both ages and in both tissues the Fat line had a higher flux, about 20% increase in the liver and up to three-fold increase (range 1·2- to 3·4-fold) in the GFP. We conclude that direct selection for fatness in mice has resulted in metabolic changes in the ratio ofde novofatty acid synthesis, and that the changes are largely detectable before 10 weeks, the age of selection.
Genetic variance and fixation probabilities at quantitative trait loci in mutation-selection balance
Authors: Keightley Peter D. 
Published: September 2009

SummaryGenetic variance and fixation probabilities are evaluated for a model of a quantitative trait at a balance between mutation, selection and drift in which many alleles can segregate at each locus. If the distribution of effects of new mutant alleles is such that mutations are unconditionally deleterious, as might be the case in natural populations, genetic variance maintained is proportional to the number of mutations occurring in the genome per generation, but is independent of the number of loci at which they appear. If selectively advantageous alleles can occur these tend to interfere to a greater extent with each others' fixation and increasing mutation rate leads to a decrease in the genetic variance as a fraction of the variance maintained in the absence of selection. Fixation probabilities of new mutant alleles approach that for neutral alleles with increasing mutation rate at a locus irrespective of their effects on fitness. The additive genetic variance contributed by the locus may appear to be ‘decoupled’ from the fixation rate of mutant alleles.
Modification of the suppressor phenotype of thymine requiring strains ofEscherichia coli
Authors: Herrington Muriel B. , Basso Johnny , Faraci Maria , Autexier Chantal 
Published: September 2009

SummaryThymine requiring strains ofEscherichia colisuppress nonsense and frameshift mutations during translation. Strains with different genetic backgrounds exhibited different nonsense suppression spectra and showed differences in the apparent suppression efficiency. Part of this strain difference is due to a presumably novel gene (tsmA) mapping near 39 min. This gene affects the spectrum and apparent efficiency of suppression, and appears to affect the utilization of thymidine.
Recent evolutionary history of the metallothionein geneMtninDrosophila
Authors: Theodore Laurent , Ho Ann-Shu , Maroni Gustavo 
Published: September 2009

SummaryA new allele of one of the metallothionein genes ofD. melanogaster,Mtn•3, sheds light on the recent evolution of this gene. In comparison to the previously studiedMtnlallele found in Canton S, this new allele,Mtn•3, produces a transcript that is 49 bases longer and 65–70 % less abundant. We detectedMtn•3in several laboratory strains as well as in isofemale lines derived from natural populations. Sequence comparison showed thatMtn•3differs fromMtnlin that it has: (a) base-pair substitution and an extra 49 bp-segment in the 3' untranslated region, (b) a substitution in the coding region that replaces the terminal Glu40 inMtnlwith Lys40, and (c) two base-pair substitutions in the promoter region. TheMtn•3-type was detected in six species of themelanogastergroup by restriction analysis, and this result was confirmed by sequencing the D. simulans Mtn gene. ThusMtn•3, which produces a less abundant transcript, appears to be the oldest of the two alleles. We also found that the duplications previously isolated from natural populations all derived fromMtnl, the more recent allele. Thus, two evolutionary steps: Mtn•3 toMtnlandMtnltoDp(Mtnl), are accompanied by an overall 5- to 6-fold increase of RNA accumulation. The two changes seem to have occurred in non-African populations since Mtn•3 but notMtnlwas detected in our sample from tropical Africa, whileMtnlandDp(Mtnl) are prevalent in European and North American samples.
Characterization ofMR(P) strains ofDrosophila melanogaster: the number of intact P elements and their genetic effect
Authors: Eeken Jan C. J. , Romeyn Ron J. , De Jong Anja W. M. , Yannopoulos George , Pastink Albert 
Published: September 2009

SummaryTo study the effect of mutagenic/carcinogenic agents on P-element transposition, the P strains used should be denned, especially with respect to the number of intact and functional P elements present. In this investigation, the relation between the number of complete P elements present in dysgenic males and P-insertion mutagenesis was studied in severalMR(P) strains. The main conclusions from this investigation are: (1) Complete P elements can be present in the genome without genetic activity (even in a ‘dysgenic’ cross). As a consequence, the number of complete P elements present in particular dysgenic flies, is not necessarily an indication of their dysgenic genetic activity. (2) TheMR-h12/Cystrain carries two complete P elements, one on the X chromosome without and one on theMRchromosome with genetic activity (making this strain most suitable for studies on P-transposition mechanisms).
Expression ofcis-regulatory mutations of thewhitelocus in metafemales ofDrosophila melanogaster
Authors: Birchler James A. 
Published: September 2009

SummaryAt thewhite eyecolour locus, there are a number of alleles that have altered expression between males and females. To test these regulatory mutations of thewhite eyecolour locus for their phenotypic expression in metafemales (3X; 2A) compared to diploid females and males, eleven alleles or transduced copies ofwhitewere analysed. Two alleles that exhibit dosage compensation between males and females (apricot, blood) also exhibit dosage compensation in metafemales.White-ivoryandwhite-eosin, which fail to dosage compensate in males compared to females, but that are distinct physical lesions, also show a dosage effect in metafemales. Two alleles with greater expression in males than females (spotted, spotted-55) exhibit even lower expression in metafemales. Lastly, five transduced copies ofwhite carryingthree different lengths of the white promoter, but that all exhibit higher expression in males, show reduced expression in metafemales, exhibiting an inverse correlation between the level of expression and the dosage of the X chromosome. Because these alleles ofwhiterespond to dosage compensation in metafemales as a continuum of the male and female responses, it is concluded that the same basic mechanism of dosage compensation is involved and that the dosage of the X chromosome conditions the sexually dimorphic expression.
Regulation of fitness in yeast overexpressing glycolytic enzymes: parameters of growth and viability
Authors: Rosenzweig R. F. 
Published: September 2009

SummaryCurrent models predict that large increases over wild-type in the activity of one enzyme will not alter an organism's fitness. This prediction is tested in Saccharomyces cerevisiae through the use of a high copy plasmid that bears one of the following: hexokinase B (HEXB), phosphoglucose isomerase (PGI), phosphofructokinase (PFKAandPFKB), or pyruvate kinase (PYK). Transformants containing these plasmids demonstrate a four to ten-fold increase in enzyme specific activity over either the parent strain or transformants containing the plasmid alone. Haploid and diploid transformants derived from independent backgrounds were grown on both fermentable and non-fermentable carbon sources and evaluated for several components of fitness. These include growth rate under non-limiting conditions, maximum stationary phase density, and viability in extended batch culture. Cell viability is not affected by overproduction of these enzymes. Growth rate and stationary phase density do not differ significantly among strains that overexpressHEXB, PGIor contain the vector alone.PFKA, Btransformants show reduced growth rate on glucose in one background only. For these loci the current model is confirmed. By contrast, when grown on glucose, yeast overexpressingPYKdemonstrate reduced growth rate and increased stationary phase density in both backgrounds. These effects are abolished in cells containing plasmids with a Tn5 disrupted copy of thePYKgene. Our results are consistent with reports that the PYK locus may exert control over the yeast cell cycle and suggest that it will be challenging to model relations between fitness and activity for multifunctional proteins.