bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dominance is not necessary for heterosis: a two-locus model
Authors: Minvielle Francis 
Published: September 2009

SummaryUnder a two-locus model with additive genes which combine multiplicatively to determine a quantitative trait, heterosis is generally observed in the F1 It is positive only if both frequencies of the best allele at each locus are not higher in the same parental population. In the F2, heterosis depends on the rate of recombination between the two loci. If linkage is tight, F1 superiority is nearly halved in the F2. But if the two genes are independent, heterosis is maintained in the F2 at the same level as in the F1.
Quantitative genetic variability maintained by mutation-stabilizing selection balance in finite populations
Authors: Keightley Peter D. , Hill William G. 
Published: September 2009

SummaryModels of variability in quantitative traits maintained by a balance between mutation and stabilizing selection are investigated. The effects of mutant alleles are assumed to be additive and to be randomly sampled from a stationary distribution. With a two-allele model the equilibrium genetic variance in an infinite population is independent of the distribution of mutant effects, and dependent only on the total number of mutants appearing per generation. In a finite population, however, both the shape and standard deviation of the distribution of mutant effects are important. The equilibrium variance is lower when most of the mutational variance is contributed by few genes of large effect. Genes of small effect can eventually contribute substantially to the variance with increasing population size (N.) The equilibrium variance can be higher in a finite than an infinite population since near-neutral alleles can drift to intermediate frequencies where selection is weakest. Linkage leads to a reduction in the maintained variance which is small unless linkage is very tight and selection is strong, but the reduction becomes greater with increasingNsince more mutants segregate. A multi-allele model is simulated and it is concluded that the two-allele model gives a good approximation of its behaviour. It is argued that the total number of loci capable of influencing most quantitative traits is large, and that the distribution of mutant effects is highly leptokurtic with the effects of most mutants very small, and such mutants are important in contributing to the maintained variance since selection against them is slight. The weakness of the simple optimum model is discussed in relation to the likely consequences of pleiotropy.
Genomic organization inCaenorhabditis elegans: deficiency mapping on linkage group V(left)
Authors: Rosenbluth Raja E. , Rogalski Teresa M. , Johnsen Robert C. , Addison Linda M. , Baillie David L. 
Published: September 2009

SummaryIn this study we genetically analyse a large autosomal region (23 map units) inCaenorhabditis elegans.The region comprises the left half of linkage group V [LGV(left)] and is recombinationally balanced by the translocationeT1(III; V). We have used rearrangement breakpoints to subdivide the region from the left end of LGV todaf-11into a set of 23 major zones. Twenty of these zones are balanced byeT1.To establish the zones we examined a total of 110 recessive lethal mutations derived from a variety of screening protocols. The mutations identified 12 deficiencies, 1 duplication, as well as 98 mutations that fell into 59 complementation groups, significantly increasing the number of available genetic sites on LGV. Twenty-six of the latter had more than 1 mutant allele. Significant differences were observed among the alleles of only 6 genes, 3 of which have at least one ‘visible’ allele. Several deficiencies and 3 alleles oflet-336were demonstrated to affect recombination. The duplication identified in this study issDp30(V;X). Lethal mutations covered bysDp30were not suppressed uniformly in hermaphrodites. The basis for this non-uniformity may be related to the mechanism ofXchromosome dosage compensation inC. elegans.
Phenotypic characterization and genetic analysis of twenty dominant cataract mutations detected in offspring of irradiated male mice
Authors: Kratochvilova Jana , Favor Jack 
Published: September 2009

SummaryTwenty autosomal dominant cataract mutations were detected among the offspring of male mice irradiated with γ- or X-rays. The single or fractionated doses ranged from 5.34 to 10.2 Gy. The phenotypic manifestation and penetrance of the mutations as well as fertility and viability of the mutants were studied by extensive breeding. Manifestation of 4 mutations was limited to the lens. Sixteen mutations were characterized by multiple ocular anomalies, of which 4 mutations also affected other organs of the body. Seventy per cent of the mutations caused severe opacity of the lens or lens and cornea. Homologous hereditary diseases in man would be juvenile cataracts with serious impairment of vision or blindness. Expressivity of the lens opacities was almost constant whereas the accompanied defects varied with respect to their severity in different individuals as well as in eyes of an individual. Phenotypic differences dependent on the genetic background could not be observed. Fourteen mutations were classified as mutations with complete penetrance without any effect on viability and fertility of heterozygotes. Four other mutations were shown to be fully penetrant but the viability of the heterozygotes was impaired. Two mutations had incomplete penetrance with no viability or fertility effects. Of the 14 mutations with complete penetrance and normal viability and fertility 6 were shown to be homozygous viable, 1 semi-lethal and 7 lethal.
Age-related reactivation of an X-linked gene close to the inactivation centre in the mouse
Authors: Brown Sheila , Rastan Sohaila 
Published: September 2009

SummaryAge-related reactivation of an X-linked gene which maps close toXce, the X chromosome inactivation centre, has been observed. In five female mice which carried the X-linked coat colour geneMobloon the reciprocal translocation T(X;16)16H (Searle's translocation), and the wild-type gene on the normal X chromosome, and therefore expressed theMoblophenotype due to the non-random inactivation characteristic of Searle's translocation, progressive darkening of the coat was observed as the animals aged. This is due to reactivation of the previously inactivated wild-type gene at theMolocus on the normal X chromosome. As theMolocus is located 4 cM distal toXce, the X chromosome inactivation centre, these observations provide evidence of age-related instability of inactivation of an X-linked gene close to the inactivation centre.
A transposable genetic element associated with positive regulation of G6PD gene expression inDrosophila melanogaster
Authors: Itoh Masanobu , Iwabuchi Mari , Yorimoto Naoki , Hori Samuel H. 
Published: September 2009

SummaryThe DNA structures around the G6PD coding region in three high-G6PD activity mutants and their low-activity revertants ofDrosophila melanogasterwere analysed by Southern blot using a cloned G6PD gene as a probe. As a result, two kinds of insertion sequences were found; one was present just 5′ to exon I (Ins1), and the other within the intron (Ins2). The Ins1 sequence was 3·5 Kb in two mutants and 2·9 Kb in one mutant. In both cases, it consisted of a core sequence either 1·2 or 0·6 Kb long flanked by terminal repeats. On the other hand, low-activity revertants possessed either a defective Ins1 or no Ins1. The Ins2 sequence was found in all mutants and revertants, but not in Canton S. Although a recombinant phage carrying the DNA fragment spanning the entire Ins1 has not been obtained, sequencing data of the clone containing only the terminal repeats demonstrated that the repeats are defective P elements. Comparison of the genomic DNA structures of mutants and revertants suggested that the element responsible for the positive regulation of the G6PD gene in the mutants would probably be the core sequence, but not the flanking defective P elements. It was also conjectured that the 1·2 Kb core sequence might be composed of two identical elements, which might transpose independently.
The epistasis ofAdhandGpdhallozymes and variation in the ethanol tolerance ofDrosophila melanogasterlarvae
Authors: McKechnie Stephen W. , Geer Billy W. 
Published: September 2009

SummaryThe role of epistatic interaction of allozymes in the determination of variation in larval ethanol tolerance ofDrosophila melanogasterwas examined. Isofemale lines from the Tahbilk Winery were made homozygous for different common alleles of alcohol dehydrogenase (Adh) and sn-glycerol-3-phosphate dehydrogenase (Gpdh). When fed 6% ethanol, all the lines had reduced survival and, in the survivors, reduced body weight and lengthened development time. A strong positive correlation between tolerance and development time suggested that alleles responsible for slowing development on ethanol also increased ethanol tolerance. Analysis of larval ethanol tolerance over four generations showed that larvae of theAdhffGpdhff, andAdhssGpdhssallelic combinations were more tolerant than larvae with the other combinations. However, these genotypes were not associated with the slowing of development nor the weight loss on ethanol. Hence, larvae with certain combinations ofAdhandGpdhallozymes may have a greater capacity to metabolize ethanol and be more tolerant to its toxic effects.
A steep cline for mitochondrial DNA in Danish mice
Authors: Vanlerberghe F. , Boursot P. , Nielsen J. T. , Bonhomme F. 
Published: September 2009

SummaryOne hundred and ninety-eight mice trapped along a south–north transect through the Danish hybrid zone betweenMus musculus domesticusandM. m. musculuswere typed for mitochondrial DNA (mtDNA), theYchromosome and ten autosomal loci encoding diagnostic proteins. The southern (domesticus) populations display two mtDNA variants (S1 and S2) and the northern (musculus) have a third mtDNA variant (N) ofdomesticusorigin. Across the hybrid zone defined by ten autosomal loci, there is a steep dine between the southern and northern types of mtDNA. As well as confirming an earlier finding that Danishmusculusall have adomesticusmtDNA (Ferriset al.1983a, &b), our results show that this mtDNA takeover is not the result of a persistent mitochondrial gene flow between the two subspecies. While the coincident dines for the ten autosomal loci and the abrupt dine for theYchromosome can be explained by selection, it is less likely to be the case for the mtDNA exchanges. We discuss the possible role of sex-linked migration and genetic drift to account for the distribution of the mitochondrial variants.
The localization ofG6pd, glucose-6-phosphate dehydrogenase, andmdx, muscular dystrophy in the mouseXchromosome
Authors: Peters J. , Ball S. T. , Charles D. J. , Pretsch W. , Bulfield Grahame , Miller D. , Chapman V. M. 
Published: September 2009

SummaryA low activity mutant of glucose-6-phosphate dehydrogenase,G6pda-m1Neuhas been used to positionG6pdin the mouseXchromosome. Linkage tests withtabby,Taandharlequin,Hq, indicate a likely gene order ofHq–G6pd–Ta. Muscular dystrophy,mdx, has been located by two-and three-point crosses usingHprt,Pgk-1andMobloand suggest a gene order ofHprt–mdx–Pgk-1–Moblo. Together with existing linkage data a tentative order for the seven loci isHq–Hprt–G6pd–mdx–Ta–Pgk-1–Moblo. The relative positions ofG6pdandmdxhave not been directly tested andG6pdis assigned provisionally proximal tomdx. In the three point test usingHq,G6pdandTathe recombination frequency found betweenHqandTawas 9·9 ± 2·6%, substantially less than the value of 20·5 ± 2·1% reported by Isaacsonet al.(1974).
Insertion-deletion variation at theyellow-achaete-scuteregion in two natural populations ofDrosophila melanogaster
Authors: Beech Robin N. , Brown Andrew J. Leigh 
Published: September 2009

SummaryWe have surveyed the region of theXchromosome ofDrosophila melanogasterwhich encodes theyellow, achaeteandscutegenes for restriction map variation. Two natural populations, one from North Carolina, U.S.A. and the other from southern Spain were screened for variation at about 70 restriction sites and for variation due to DNA insertion or deletion events in 120 kilobases of DNA. Mean heterozygosity per nucleotide was estimated to be 0·0024 and 15 large insertions were found in the 49 chromosomes screened. Extensive disequilibrium between polymorphic sites was found across much of the region in the North Carolina population. The frequency of large insertions, which usually correspond to transposable genetic elements, is significantly lower than has been observed in autosomal regions of the genome. This is predicted forX-linked loci by certain models of transposable element evolution, where copy number is restricted by virtue of the recessive deleterious effects of the insertions. Our results appear to support such models. The deficiency of insertions may in this case be enhanced by hitch-hiking effects arising from the high level of disequilibrium.
Thein vivoandin vitrotransmission frequencies of thetw5-haplotype in mice
Authors: Garside William , Hillman Nina 
Published: September 2009

SummaryThe recessivetω5-haplotype, a complete haplotype, is transmitted by heterozygous male mice at very high frequencies (> 0·90) in normal matings. The present studies were undertaken to determine the effects of delayed matings andin vitrofertilizations on this phenotypic expression. Males carrying thetω5-haplotype ( + /tω5) were first tested for their frequencies of transmission of the mutant 17th chromosome in both normal and delayed matings. Spermatozoa obtained from these same males were then used to fertilize eggsin vitro.Thein vivoandin vitrotransmission frequencies were found to be statistically equivalent in all types of inseminations. Anin vitrofertilization time course study showed that the same percentages of eggs are fertilized bytω5- bearing spermatozoa when the gametes are coincubated for either 2 or 6 h. The data lead to the conclusion that the transmission frequency of thetω5-haplotype is not affected either by the length of time elapsing between insemination and fertilization or by the environment in which fertilization occurs.
The mutational load of a multigene family with uniform members
Authors: Ohta Tomoko 
Published: September 2009

SummaryThe mutational load of a multigene family with uniform members was studied by computer simulations. Two models of selection, truncation and exponential fitness, were examined, by using a simple model of gene conversion. It was found that the load is much smaller than the Haldane–Muller prediction under the truncation selection, and that it becomes approximately equal to the value calculated by the formula,nv(1 −q)/(m−nq), wherenis the copy number,vis the rate of detrimental mutation per gene copy,mis the truncation point in terms of the number of detrimental genes eliminated, andqis the equilibrium frequency of detrimental mutation. However the equilibrium frequency cannot be analytically obtained. For the exponential fitness model, the load is close to the Haldane–Muller value. When there is no gene conversion, the load becomes larger than the cases with conversion both for the truncation and the exponential fitness models. Thus, gene conversion or other mechanisms that are responsible for contraction–expansion of mutants on chromosomes helps eliminating deleterious mutations occurring in multigene families.
Mutant alleles of the meiotic locus,mei-9, differ in degree of effects on rod chromosome magnification and ring chromosome transmission inDrosophila
Authors: Komma Donald J. , Graves Heath , Endow Sharyn A. 
Published: September 2009

SummaryTwo mutant alleles of the meiotic locus,mei-9, have been examined for their effect on magnification of a rodXbbchromosome and transmission of a ringXbbchromosome under magnifying conditions. Our results indicate that the effects of these two mutations are allele-specific:mei-9astrongly inhibits both rod chromosome magnification and ring chromosome loss under magnifying conditions, whilemei-9bhas a smaller inhibitory effect on rod chromosome magnification and on the transmission of ring chromosomes under magnifying conditions. These observations can be explained by a difference in leakiness between the two alleles. Our results demonstrate that mutants defective in excision repair and repair replication inhibit ribosomal gene magnification. This suggests that a component of the excision repair pathway is involved in the process of magnification.
Responses to divergent selection for plasma concentrations of insulin-like growth factor-1 in mice
Authors: Blair H. T. , McCutcheon S. N. , Mackenzie D. D. S. , Gluckman P. D. , Ormsby J. E. , Brier B. H. 
Published: September 2009

SummaryA divergent selection experiment with mice, using plasma concentrations of insulin-like growth factor-1 (IGF-1) at 42 days of age as the selection criterion, was undertaken for 7 generations. Lines were not replicated. To obtain sufficient plasma for the IGF-1 assay, blood from four individuals was volumetrically bulked to obtain a litter mean IGF-1 concentration. This necessitated the use of between family selection. Although inbreeding accumulated in a linear fashion in each of the high, control and low lines, the rates were different for each line (3·6, 1·6 and 5·3% per generation for the high, control and low lines, respectively). As a consequence, the effects of selection and inbreeding are confounded in this experiment. Divergence between the high and low lines in plasma concentrations of IGF-1 continued steadily until generation 5. In generations 6 and 7, there was a reduced degree of divergence and this contributed towards the low realized heritability value of 0.15 ± 0.12. Six-week liveweight showed a steady positive correlated response to selection for or against plasma concentrations of IGF-1 until generation 4 (high-low difference = 1·7 g = 12%). In generation 5, a substantial drop in 6-week liveweight in the low line relative to both the high and control lines occurred (high-low difference, 3·9; g, 25%). This difference was maintained until generation 7.This experiment suggests that genetic variation exists at 6 weeks of age in plasma concentrations of IGF-1 in mice. Furthermore, genetic covariation between plasma IGF-1 concentrations and liveweight at 6 weeks of age is likely to be positive. Further experiments have been initiated to examine these theories.
A genetic model of interpopulation variation and covariation of quantitative characters
Authors: Zeng Zhao-Bang 
Published: September 2009

SummaryEvolutionary consequences of natural selection, migration, genotype–environment interaction, and random genetic drift on interpopulation variation and covariation of quantitative characters are analysed in terms of a selection model that partitions natural selection into directional and stabilizing components. Without migration, interpopulation variation and covariation depend mainly on the pattern and intensities of selection among populations and the harmonic mean of effective population sizes. Both transient and equilibrium covariance structures are formulated with suitable approximations. Migration reduces the differentiation among populations, but its effect is less with genotype–environment interaction. In some special cases of genotype–environment interaction, the equilibrium interpopulation variation and covariation is independent of migration.
Isolation ofBacillus subtilistransformation-deficient mutants and mapping of competence genes
Authors: Mastromei Giorgio , Barberio Claudia , Pistolesi Stefania , Polsinelli Mario 
Published: September 2009

SummaryWe have isolated and characterized 48Bacillus subtiliscompetence-deficient mutants. The mutants, obtained by nitrososoguanidine mutagenesis or by insertional mutagenesis with transposon Tn917, had a reduced transformation frequency and a wild-type transduction frequency. Thecommutations were mapped by PBS1 transduction and at least four newcomgenes have been identified. The mutants were also characterized for their capacity to bind and take up the transforming DNA.
Differences in allele frequencies ofAatbetween high- and mid-rocky shore populations ofLittorina saxatilis(Olivi) suggest selection in this enzyme locus
Authors: Johannesson Kerstin , Johannesson Bo 
Published: September 2009

SummarySamples of the intertidal prosobranchLittorina saxatiliswere collected along vertical transects from high- to mid-store levels at five different geographic locations of western Europe. Electrophoretic screening of ten metabolic enzymes revealed five highly polymorphic loci. Four of these showed no or few significant differences in allele frequencies between high- and mid-shore samples ofLittorina saxatilis. The fifth locus,Aat(aspartate aminotransferase, EC 2.6.1.1), showed clinal variation in allele frequencies over the few metres of each transect, suggesting that this locus, or a coupled locus, is under selection with a slow allele (Aat100) favoured in mid-shore habitats and a faster allele (Aat120) selected for in the high littoral fringe.
Comparison of the regulation of P elements in M and M′ strains ofDrosophila melanogaster
Authors: Ronsseray Stéphane , Lehmann Monique , Periquet Georges 
Published: September 2009

SummaryM and M′ strains ofDrosophila melanogasterin the P-M system of hybrid dysgenesis were compared in two series of tests, with the following results. (1) Thesinged-weakhypermutability regulation test showed that M′ strains had lower P excision rates than M strains, suggesting that P-elements repression must occur in M′ strains although it is not detectable by gonadal dysgenesis assays. (2) The evolution of mixed P + M and mixed P + M′ populations was compared, using a strong P strain. The P + M cultures invariably evolved in a few generations into strong P cultures, while the P + M′ cultures evolved into P-type cultures with reduced P-factor potentials. However, after 30 generations of culture, both these types of mixed cultures had similar P copy numbers, suggesting that regulation of copy number had occurred in them.
Non-additive inheritance of glucose phosphate isomerase activity in mice heterozygous at theGpi-1sstructural locus
Authors: West John D. , Flockhart Jean H. 
Published: September 2009

SummaryThe activity of blood glucose phosphate isomerase (GPI-1) in mice heterozygous for various alleles at theGpi-1sstructural locus (heterozygotesa/b, a/candb/c) was significantly higher than expected, on the basis of additive inheritance, from the levels in parental homozygotes. Moreover, the GPI-1 activity was higher ina/bheterozygotes than in either parent (heterosis). Studies of heat stability with kidney homogenates revealed that the relative stabilities of GPI-1 dimers was AA > AB > BB > AC ≥ BC > CC. Differences in dimer stabilitiesin vivowould affect the total GPI-1 levels in heterozygotes and could account for non-additive inheritance but would be insufficient to explain heterosis for GPI-1 activity. Other possible contributing factors include unequal production or stability of monomers, or higher catalytic activity of heterodimers. Monomers could also associate non-randomly but this would not be sufficient to explain heterosis. It is clear that non-additive inheritance patterns may be produced by variants of either structural or regulatory genes.