bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mariner, Mosand associated aberrant traits inDrosophila mauritiana
Authors: Jacobson James W. 
Published: September 2009

SummaryA suite of aberrant genetic traits, including increased mutation rate, sex-limited mutation and distorted transmission ratios, was produced among progeny of genetic crosses between two strains ofDrosophila mauritianawhen a paternally contributedMosexcision factor is placed into a non-Mosgenetic background. In the reciprocal cross, involving maternally contributedMosandMosassociated cytoplasm, the same genetic abnormalities are not observed. Differential effects onmarinerexcision in germ-line versus somatic tissue are apparent. BecauseMosis known to influence the mobility of themarinertransposable element, these traits may be associated withmarinerexcision and/or transposition.
‘Exceptional sons’ fromDrosophila melanogastermothers carrying a balancerXchromosome
Authors: Hutter Pierre 
Published: September 2009

SummaryThis study reports on exceptional males which are obtained by usingDrosophila melanogastermothers carrying the balancersIn(l)FM6 orIn(l)FM7 as one of theirXchromosomes. The phenomenon was first observed in interspecific crosses betweenD. melanogasterfemales and males of its closest relatives which normally produce unisexual female hybrid progeny. Whereas hybrid sons from these crosses die as third instar larvae, the presence of the particularXbalancers in the mother allows a low percentage of sons to survive. Similar sterile males are also observed among non- hybrid flies. Data are presented which suggest that the males thus generated could be hyperploid for part of theirXchromosome as a result of a meiotic event in their mothers or else they could start life as female zygotes and change sex through a mitotic event at an early stage.
Segregation ratios withinSegregation Distorterlines ofDrosophila melanogasterconform to a beta-binomial distribution
Authors: Sharp Cecil B. , Hilliker Arthur J. 
Published: September 2009

SummarySegregation Distorter(SD) chromosomes are preferentially recovered fromSD/SD+males due to the dysfunction of sperm bearing theSD+chromosome. The proportion of offspring bearing theSDchromosome is given the symbolk. The nature of the frequency distribution ofkwas examined by comparing observedkdistributions produced by six differentSDchromosomes, each with a different mean, withkdistributions predicted by two different statistical models. The first model was one where thekof all males with a givenSDchromosome were considered to be equal prior to the determination of those gametes which produce viable zygotes. In this model the only source of variation ofkwould be binomial sampling. The results rigorously demonstrated for the first time that the observedkdistributions did not fit the prediction that the only source of variation was binomial sampling. The next model tested was that the prior distribution of segregation ratios conformed to a beta distribution, such that the distribution ofkwould be a beta-binomial distribution. The predicted distributions of this model did not differ significantly from the observed distributions ofkin five of the six cases examined. The sixth case probably failed to fit a beta-binomial distribution due to a major segregating modifier. The demonstration that the prior distribution of segregation ratios ofSDlines can generally be approximated with a beta distribution is crucial for the biometrical analysis of segregation distortion.
Reduction of wild-typeXchromosomes with theYbb−chromosome ofDrosophila melanogaster
Authors: Palumbo Gioacchino , Endow Sharyn A. , Hawley R. Scott 
Published: September 2009

SUMMARYTheYbb−chromosome has been previously shown to induce reduction ofXchromosome ribosomal genes inXbb/Ybb−orXbb+/Ybb−flies. These reduction events are presumed to arise as one of the two products of unequal sister chromatid exchanges, which result in both magnified and reduced products. Bobbed reduced chromosomes may also arise as products of other recombinative events such as intrachromatid deletions. In this report we use theYbb−chromosome to reduce the number of ribosomal genes present onXchromosomes from two wild-type stocks under ‘non-magnifying’ conditions. We then show that the bobbed reducedXchromosomes show no detectable difference in their Southern blot rDNA patterns when compared with the parental wild-typeXchromosome. This indicates that reduction events do not preferentially delete certain repeat classes, and supports previous observations that the repeat types present in theD. melanogaster Xchromosome nucleolus organizer are not significantly clustered.
Position and orientation in the metaphase equator of an interchange quadrivalent of Allium triquetrum
Authors: Rickards Geoffrey K. 
Published: September 2009

SUMMARYThe position and orientation of an interchange quadrivalent in flattened, lateral views of metaphase I were studied in pollen-mother-cells of an interchange heterozygote of Allium triquetrum. The quadrivalent is most often located in marginal rather than central positions in the equator. Moreover, when positioned marginally the quadrivalent is more often than expected found in adjacent orientation, whilst when positioned centrally it is more often than expected found in alternate orientation. Consequently, the frequency of alternate (genetically balanced) orientation in the quadrivalent varies sharply according to whether data are obtained from more marginal or more central positions in the metaphase plate.
Evidence for a nonsense mutation at theniaDlocus ofAspergillus nidulans
Authors: Martinelli S. D. , Roberts T. J. , Sealy-Lewis H. M. , Scazzocchio C. 
Published: September 2009

SUMMARYTwo mutations at theniaDlocus (structural gene for nitrate reductase apo-protein) are genotypically suppressible. Both mutations result in loss of nitrate reductase enzyme activity and cross reacting material and are non complementing, nonleaky and highly revertible. They have the properties of nonsense mutations. This implies that some of the allele specific suppressors, which act on these and alleles at several other loci, are nonsense suppressors.
The effect of selection on brain and body size association in rats
Authors: Atchley William R. 
Published: September 2009

SUMMARYChanges 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

SUMMARYExpression 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

SUMMARYMice 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

SummaryIsofemale 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

SummaryThe 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

SummaryIn 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

SummaryPosition-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

SummaryThen0coalescent 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

SummaryA 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

SummarySkin 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

SummaryThe 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.