bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of selection on brain and body size association in rats
Authors: Atchley William R.
Published: September 2009

Changes in brain size, body size and their co variance are reported from a long-term replicated directional selection experiment on body weight gain in rats. Two strains had been selected for increased and two for decreased weight gain between 3 and 9 weeks of age, and there were two randomly selected control lines. Selection produced significant changes in body weight in all selected lines. Divergence from the controls occurred in brain size in those strains selected for increased weight gain; no significant divergence was found for the strains selected for decreased weight gain. Divergence among unselected control lines suggests that genetic drift occurred in expression of brain size. Sexual dimorphism in response to selection results from sex differences in heritabilities and genetic correlations in relevant traits. In spite of considerable change in body size and brain size, no significant change in their covariation occurred either between the selection lines or between sexes. The relevance of these results to a brain and body size ‘scaling effect’ during evolutionary divergence is discussed.
Organization of polygenic systems: Cell death modifiers from natural populations ofDrosophila melanogaster
Authors: Thompson James N. , Spivey William E.
Published: September 2009

Expression of three wing-cell death mutants inDrosophilamelanogaster was used to survey cryptic polygenic modifiers of cell death in wild type strains. Females carrying the X-linked mutants Beadex-3, notchoid and scalloped were crossed to males from each of 20 isofemale strains. Phenotypic variation in the amount of cell death was measured in F1mutant males that were heterozygous for polygenic loci segregating in the wild strains. As expected, each mutant uncovered a broad range of polygenic variation among strains. Yet, when cluster analyses were used to evaluate the degree of correlation among the expressions ofBx3,sdandnd, the isofemale strains could be partitioned into a small number of groups that were similar in the effects they had upon the severity of cell death. Chromosome mapping of one cell death suppressor strain demonstrated that different polygenic loci could produce the same phenotype in different mutant backgrounds.
Evidence for a major gene for rapid postweaning growth in mice
Authors: Bradford G. E. , Famula T. R.
Published: September 2009

Mice gaining 3 or more standard deviations above the mean were noted beginning in generation 25 in a line selected for high 21–42 day weight gain. The exceptional growth rate appears to be due to an autosomal recessive gene, based on the following: (1) the exceptional individuals appeared suddenly, in only one of 2 closely related sublines; (2) mating high growth individuals to unrelated, normal size strains produces relatively uniform F1's with mean gains below the mid-parent average; (3) F2's have a distribution markedly skewed towards high gain and a coefficient of variation approximately double that of F1's; (4) true breeding high growth strains can be established in one generation by intermating the largest F2's; (5) intermating normal F2's produces progenies with a distribution similar to the F1except for a few large segregates; (6) high growth segregates have been obtained in F2's from each of 4 successive backcrosses to the C57BL/6 inbred line. The symbolhg(high growth) is proposed for the postulated gene, which appears to be completely recessive. Frequency of positively identified segregates in F2's and backcrosses is on average less than 25 and 50%, due probably to some overlap ofHg- andhghgdistributions. Gain ofhghgindividuals from 21–42 days is 30–50% higher than ofHg- contemporaries; mature weight is also much higher, while 21-day weight ofhghgindividuals in segregating litters is slightly lower. Fertility of homozygotes ranges from normal to as much as 40% lower than for comparableHg- mice;hghgmice are not obese. The gene may provide a useful model for study of regulation of mammalian growth.
A latitudinal cline inP–Mgonadal dysgenesis potential in AustralianDrosophila melanogasterpopulations
Authors: Boussy Ian A.
Published: September 2009

Isofemale lines ofDrosophila melanogasterfrom six localities along the east coast of Australia, spanning 2900 km and 26 degrees of latitude, were assayed for their gonadal dysgenesis characteristics in theP–Msystem of hybrid dysgenesis. A strong clinal pattern with latitude was discovered. From north to south, the first two populations were typical strongPpopulations, and the next population was moderateP. The next population to the south was neutral (Q), with some weakPand weakMcharacteristics. The two southernmost populations were typicalMpopulations. Much variance inPactivity inPpopulations and in susceptibility toPactivity inMpopulations was detected among isofemale lines. This clinal pattern with latitude of theP–Msystem is paralleled by similar clinal patterns for frequencies of common cosmopolitan inversions and of certain allozymes in Australia. A model of introductions of flies with different characteristics in the north and south could account for theP–Mclinal pattern, but cannot account for an intermediateQpopulation, nor establish the inversion and isoenzyme dines at the same time. Current models of transposable element population dynamics are limited to single population dynamics, and are therefore inadequate for these clinal data.
Damage in DNA of an infecting phage T4 shifts reproduction from asexual to sexual allowing rescue of its genes
Authors: Bernstein Carol
Published: September 2009

The selective advantage of sexual reproduction is widely regarded as a major unsolved problem in biology. Recently, it has been proposed that the fundamental selective advantage of sex is its promotion of recombinational repair and hence survival of DNA in the germ line of organisms. A bacteriophage T4 system was set up to test this theory. After a phage T4 injects its DNA into anEscherichia colicell it quickly establishes a barrier, through its immunity function, to infection by a second phage T4, arriving at a later time. This barrier causes phage T4 to reproduce asexually. The immunity barrier has a selective advantage in preserving the host cell as a sole resource for the first phage. If the first phage's DNA is damaged by UV irradiation, however, it has a reduced probability of being able to survive in the host cell when it is there alone. It was found that UV irradiation, in addition to reducing the first phage's viability, also prevents the first phage from raising an effective immunity barrier. This UV-induced reduction in immunity now allows sexual interaction with later-arriving secondary phage or sexual reproduction. It was found that these secondary phage enhanced survival of genes of the UV-damaged first phage. This supports the theory that under DNA-damaging conditions, which should be prevalent in nature, sex would have a selective advantage.
The fitness consequences ofPelement insertion inDrosophila melanogaster
Authors: Eanes Walter F. , Wesley Cedric , Hey Jody , Houle David , Ajioka James W.
Published: September 2009

In this study we estimate the frequency at whichP-element insertion events, as identified byin situhybridization, generate lethal and mild viability mutations. The frequency of lethal mutations generated per insertion event was 0·004. Viability dropped an average of 1% per insertion event. Our results indicate that it is deletions and rearrangements resulting from the mobilization ofPelements already in place and not the insertionsper sethat cause the drastic effects on viability and fitness observed in most studies of P–M dysgenesis-derived mutations. Elements of five other families (I, copia,412,B104, andgypsy) were not mobilized in these crosses. Finally, we contrast the density ofPelements on theXchromosome with the density on the four autosomal arms in a collection of thirty genomes from an African population. The relative number ofPelements on theXchromosome is too high to be explained by either a hemizygous selection or a neutrality model. The possible reasons for the failure to detect selection are discussed.
A correlation between development time and variegated position effect inDrosophila melanogaster
Authors: Michailidis John , Murray Neil D. , Graves Jennifer A. Marshall
Published: September 2009

Position-effect variegation is a phenomenon in which cell-autonomous genes, normally expressed in all cells of a tissue, are expressed in some cells but not in others, leading to a mosaic tissue. Variegation occurs when a normally euchromatic gene is re-positioned close to heterochromatin by chromosome rearrangement. The extent of variegation is known to be influenced by a number of environmental and genetic factors. In the courss of investigations of the influence of the pH of larval medium on the extent of eye-colour variegation in In(1)ωm4Drosophila melanogaster, we have found that the extent of variegation depends on development time. Flies reared at pH 2·6 develop slowly and show more extreme variegation than those reared at higher pH. This effect, as well as variations within the pH treatments, can be accounted for by differences in development time. The observed regression relationship between variegation and development time also appears to accommodate the influences of temperature on both variables. We suggest that development time may account causally for the reported influences of a number of environmental agents (temperature, crowding, chemicals) on variegation. Ways in which this might occur are discussed in the context of models of the molecular basis of differential gene activity.
The coalescent in two partially isolated diffusion populations
Authors: Takahata Naoyuki
Published: September 2009

Then0coalescent of Kingman (1982a,b) describes the family relationships among a sample ofn0individuals drawn from a panmictic species. It is a stochastic process resulting fromn0− 1 independent random events (coalescences) at each of whichn(2 ≤n≤n0) ancestral lineages of a sample are descended fromn− 1 distinct ancestors for the first time. Here a similar genealogical process is studied for a species consisting of two populations with migration between them. The main interest is with the probability density of the time length between two successive coalescences and the spatial distribution ofn− 1 ancestral lineages over two populations whennton− 1 coalescence takes place. These are formulated based on a non-linear birth and death process with killing, and are used to derive several explicit formulae in selectively neutral population genetics models. To confirm and supplement the analytical results, a simulation method is proposed based on the underlying bivariate Markov chain. This method provides a general way for solving the present problem even when an analytical approach appears very difficult. It becomes clear that the effects of the present population structure are most conspicuous on 2 to 1 coalescence, with lesser extents onnton− 1 (3 ≤n) coalescence.This implies that in a more general model of population structure, the number of populations and the way in which a sample is drawn are important factors which determine then0coalescent.
On the role of unequal exchange in the containment of transposable element copy number
Authors: Langley Charles H. , Montgomery Elizabeth , Hudson Richard , Kaplan Norman , Charlesworth Brian
Published: September 2009

A population genetics model of the role of asymmetric pairing and unequal exchange in the stabilization of transposable element copy number in natural populations is proposed and analysed. Monte Carlo simulations indicate that the approximations incorporated into the analysis are robust in the relevant parameter ranges. Given several simple assumptions concerning transposition and excision, equal and unequal exchange, and chromosome structure, predictions of the relative numbers of transposable elements in various regions of theDrosophila melanogastergenome are compared to the observed distribution ofroo/B104elements across chromosomal regions with differing rates of exchange, and betweenXchromosomes and autosomes. There is no indication of an accumulation of elements in the distal regions of chromosomes, which is expected if unequal exchange is reduced concomitantly with normal crossing over in the distal regions. There is, however, an indication of an excess of elements relative to physical length in the proximal regions of the chromosomes, which also have restricted crossing over. This observation is qualitatively consistent with the model's predictions. The observed distribution of elements between the mid-sections of theXchromosomes and autosomes is consistent with the predictions of one of two models of unequal exchange.
Evidence of a unique developmental mechanism specifying both wool follicle density and fibre size in sheep selected for single skin and fleece characters
Authors: Moore G. P. M. , Jackson N. , Lax J.
Published: September 2009

Skin and fleece traits have been characterized in four lines of Merino sheep selected for high- and low-fibre diameter (D±) and staple length (L±) from a medium-woolled flock. Over a period of 20 years, each line responded in the desired direction, producing fleeces composed of thick or thin fibres and long or short wool staples. However, variations in the amounts of wool grown that might be expected from these procedures were compensated by changes in unselected characters. Thus a predicted difference in fleece weights between high and low staple length lines was reduced by an increase in fibre crimp frequency in L− sheep. Similarly, changes induced in fibre diameter in the D lines resulted in small effects on fleece weight in comparison to the large (and inverse) effects on follicle numbers. Towards the end of the selection regime, mean follicle density in D− sheep was twice that of D+ sheep. This intriguing response within the follicle population was examined further: an analysis of the relationship between follicle density and fibre diameter amongst the four lines revealed a highly significant, negative linear correlation. The implication of this statistical association is that the numbers of follicles initiated in skin during foetal life had a direct bearing on the sizes of wool fibres eventually produced. It was concluded that both features must be under the control of a single developmental mechanism. Since the expression of each of the characters is separated in time, the mechanism must be activated during the earlier event, i.e. at or before the phase of follicle initiation.
Structure, frequency and distribution of P elements in relation to P—M hybrid dysgenic male recombination inDrosophila melanogaster
Authors: Exley K. A. , Eggleston P.
Published: September 2009

The frequency and distribution of P elements were investigated in the third chromosomes of two wild-type strains ofDrosophila melanogasterusingin situhybridization of biotinylated probes to the polytene chromosomes. The relationship between these data and the extent of hybrid dysgenesis was determined through assays of egg production, egg hatchability (F2embryo lethality),snwdestabilization and male recombination along the third chromosome. The results suggest that P-element distribution, frequency and structure are all contributory factors in the regulation of hybrid dysgenesis. Texas 6 was shown consistently to be a stronger P strain than Texas 1, eliciting greater reductions in fertility, more extensivesnwdestabilization and higher frequencies of male recombination. Clustering of male recombination events, arising from pre-meiotic crossing over, was evident among the dysgenic progeny of each strain. Male recombination andsnwdestabilization were independently distributed among the dysgenic males studied, suggesting that these traits represent separate P-mediated functions. The third chromosome male recombination maps produced by the two strains differed significantly from each other and from the published female meiotic and polytene chromosome maps. Male recombination breakpoints were associated with the original distribution of P sequences in the two strains and the results suggest that this relationship may be closer for potentially complete P factors than for P sequences in general. An analysis of sub-lines derived from individual recombinant males revealed that chromosomal breakpoints could also be associated with novel insertions following P-element transposition.
Genome size variation in the North American sunfish genusLepomis(Pisces: Centrarchidae)
Authors: Ragland Chara J. , Gold John R.
Published: September 2009

Genome 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

The 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

The 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

Polygenic 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

Destabilization 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

InDrosophila 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

The 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

Eggs 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

Cross-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

The 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

The 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

Genetic 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

Thymine 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

A 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

To 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

At 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

Current 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.
The role oforiTintra-dependent enhanced recombination between mini-F-lac-oriTand λplac5
Authors: Carter Jeffrey R. , Patel Dipty R. , Porter Ronald D.
Published: September 2009

Recombination between F42lacand λplac5is typically 20- to 50-fold more efficient than recombination between chromosomallacand λplac5. This enhancement of recombination isrecBCD-dependent and requires the expression of genes from thetraregulon of the F factor. Also required isoriT, the origin of F factor conjugational transfer, which must be located in-cisto the cellular copy oflac. In this study we show that enhanced recombination is not supported by anoriTpoint mutant that reducesoriTfunction in conjugation. We also present evidence that the activation oforiTfor recombination enhancement involves the same strand-specific nick that is required for conjugal DNA transfer. Although it is thought that the role oforiTin recombination enhancement is related to the facilitated entry of RecBCD enzyme into the DNA duplex, we were unable to detect any double-strand breakage atoriT.
Allelism tests of 15 dominant cataract mutations in mice
Authors: Kratochvilova J. , Favor J.
Published: September 2009

Fifteen autosomal dominant mutations that cause cataract of lenses in mice were tested for allelism. The outcrosses of double mutants revealed three allelism groups, consisting of 5, 4 and 2 mutations as well as 4 mutations which segregated independently. The results indicated 7 different cataract loci in the sample of 15 mutations. The biomicroscopic examination of the eyes showed that phenotypically similar as well as very distinct cataract mutations can be alleles of the same gene. Conversely, phenotypically similar mutations were shown to be non-allelic.
Phenotypic plasticity for life-history traits inDrosophila melanogaster. III. Effect of the environment on genetic parameters
Authors: Gebhardt M. D. , Stearns S. C.
Published: September 2009

We estimated genetic and environmental variance components for developmental time and dry weight at eclosion inDrosophila melanogasterraised in ten different environments (all combinations of 22, 25 and 28°C and 0·5, 1 and 4% yeast concentration, and 0·25% yeast at 25°C). We used six homozygous lines derived from a natural population for complete diallel crosses in each environment. Additive genetic variances were consistently low for both traits (h2around 10%). The additive genetic variance of developmental time was larger at lower yeast concentrations, but the heritability did not increase because other components were also larger. The additive genetic effects of the six parental lines changed ranks across environments, suggesting a mechanism for the maintenance of genetic variation in heterogenous environments.

The variance due to non-directional dominance was small in most environments. However, there was directional dominance in the form of inbreeding depression for both traits. It was pronounced at high yeast levels and temperatures but disappeared when yeast or temperature were decreased. This meant that the heterozygous flies were more sensitive to environmental differences than homozygous flies. Because dominance effects are not heritable, this suggests that the evolution of plasticity can be constrained when dominance effects are important as a mechanism for plasticity.
Supernova(spno), a new maternal mutant producing variable-sized cleavage nuclei inDrosophila
Authors: Webster M. , Moretti P. , Brink N. G.
Published: September 2009

This paper describes a new recessive maternal lethal which disrupts normal nuclear division and migration during cleavage inDrosophila. We have named this gene locussupernova. Deletion mapping andin situhybridization have located this gene to 88 F9/89 A1 on the polytene chromosome map. The terminal mutant phenotype is characterized by the presence of many variable-sized nuclei scattered throughout the cytoplasm of the unhatched egg. Following fertilization, the initial cleavage divisions appear delayed and are often accompanied by the formation of ring-like association of chromosomes and/or chromosome bridges. Although the polymerization of tubulin into spindles occurs during the initial cleavage divisions, there appears to be both a spatial and temporal uncoupling of DNA replication from the formation and proper functioning of spindles. Eventually no functional spindles are formed, but nuclei continue to increase in size and number with increasing age of the embryo following fertilization.
The segregation ratio inwaxy-heterozygous barley plants
Authors: Frykman Ingrid , Bengtsson Bengt O.
Published: September 2009

In seven experiments the segregation ratio in barley plants heterozygous for thewaxy-gene was studied. Each experiment entailed the scoring of more than 40000 iodine-stained pollen grains from ten spikes. A significant over-representation of blue pollen grains was found in all experiments, with the segregation distortion (measured as a conversion force) ranging from 0·0063 to 0·0143. The distortion was unaffected by which of two mutations was used and which genetic background the plants had, but was stronger in 1988 than in 1987. Different statistical, methodological and biological explanations of the results are discussed.
Expression of theEscherichia coli ftsZgene: trials and tribulations of gene fusion studies
Authors: Robin Aline , D'Ari Richard
Published: September 2009

TheftsZgene ofEscherichia coli, which codes for an essential cell division protein, is subjected to multiple regulation, as shown in part with studies using anftsZ::lacZoperon fusion located on phage λJFLIOO. Using this same fusion, we sought to isolate regulatory mutants overexpressingftsZby selecting mutants able to grow on lactose. One Lac+mutant was obtained which overexpressed theftsZ::lacZfusion 70-fold. The mutation responsible for the overexpression lies in a new gene,cot, located near 56 min on theE. coligenetic map. Thecotmutation probably affects the transcription of a chromosomal open reading frame, 0RF1, lying downstream of thebioAgene and adjacent to theftzZ::lacZfusion of the λJFL100 prophage integrated atattλ. Using anftsZ84(Ts) strain, in which there was a double selection for overexpression of bothftsZ::lacZandftsZ+, no Lac+Tr mutants were obtained from 3·6 × 1010bacteria; the introduction of amutLallele, increasing spontaneous base substitution mutation rates 75-fold, did not permit us to isolate such a mutant. We conclude that Lac+ftsZ-constitutive mutations cannot be obtained in λJFL100 lysogens by a single base substitution.
Adaptation and the ‘shifting balance’
Authors: Barton N. H. , Rouhani S.
Published: September 2009

Wright proposed that there is a ‘shifting balance’ between selection within demes, random drift, and selection between demes at different ‘adaptive peaks’. We investigate the establishment and spread of new adaptive peaks, considering a chromosome rearrangement, and a polygenic character under disruptive selection. When the number of migrants (Nm) is small, demes fluctuate independently, with a bias towards the fitter peak. WhenNmis large, the whole population can move to one of two stable equilibria, and so can be trapped near the lower peak. These two regimes are separated by a sharp transition at a criticalNmof order 1. Just below this critical point, adaptation is most efficient, since the shifting balance greatly increases the proportion of demes that reach the global optimum. This is so even if one peak is only slightly fitter than the other (ΔW≈1/N), and for both strong and weak selection (Ns(Ns ≪ 1 or Ns ≫ 1). Provided thatNmvaries sufficiently gradually from place to place, the fitter peak can be established in regions whereNm≈1, and can then spread through the rest of the range. Our analysis confirms Wright's argument that if selection, migration and drift are of the same order, the ‘shifting balance’ leads to efficient evolution towards the global optimum.