bluuebunny/crossref_metadata_2025 huggingface dataset:
The accumulation of P-elements on the tip of theXchromosome in populations ofDrosophila melanogaster
Authors: Ajioka James W. , Eanes Walter F.
Published: September 2009

Little information exists about the mechanisms that determine the fate of mobile elements in natural populations. In this study we catalogue the distribution of 638 P-elements across 114Xchromosomes in samples drawn from three natural populations ofDrosophila melanogaster. There is an extremely high occurrence of elements at the tip relative to the rest of the euchromatic chromosome. We demonstrate that the distribution ofde novoinsertions of the P-element on a specific laboratory chromosome is markedly different; no P-elements were recovered at the tip in the 243 insertion events recorded. In contrast, insertion data for the π2chromosome suggests an elevated rate associated with the tip site although it does not appear sufficient to explain the large differential accumulation on wild chromosomes. This raises the issue of inter chromosome (or tip) variation in relative rates, as well as the possibility that rates of elimination are lower at the tip.
Genic differentiation and origin of Robertsonian populations of the house mouse (Mus musculus domesticusRutty)
Authors: Britton-Davidian Janice , Nadeau Joseph H. , Croset Henri , Thaler Louis
Published: September 2009

This paper examines the relation between chromosomal and nuclear-gene divergence in 28 wild populations of the house mouse semi-species,Mus musculus domesticus, in Western Europe and North Africa. Besides describing the karyotypes of 15 of these populations and comparing them to those of 13 populations for which such information was already known, it reports the results of an electrophoretic survey of proteins encoded by 34 nuclear loci in all 28 populations. Karyotypic variation in this taxon involves only centric (or Robertsonian) fusions which often differ in arm combination and number between chromosomal races. The electrophoretic analysis showed that the amount of genic variation within Robertsonian (Rb) populations was similar to that for all-acrocentric populations, i.e. bearing the standard karyotype. Moreover, divergence between the two types of populations was extremely low. These results imply that centric fusions in mice have not modified either the level or the nature of genic variability. The genetic similarity between Rb and all-acrocentric populations is not attributed to the persistence of gene flow, since multiple fusions cause marked reproductive isolation. Rather, we attribute this extreme similarity to the very recent origin of chromosomal races in Europe. Furthermore, genic diversity measures suggest that geographically separated Rb populations havein situand independent origins. Thus, Rb translocations are probably not unique events, but originated repeatedly. Two models are presented to explain how the rapid fixation of a series of chromosomal rearrangements can occur in a population without lowering variability in the nuclear genes. The first model assumes that chromosomal mutation rates are between 10−3and 10−4and that populations underwent a series of transient bottlenecks in which the effective population size did not fall below 35. In the second model, genic variability is restored following severe bottlenecks, through gene flow and recombination.
Correlation between genetic distances based on single loci and on skeletal morphology in inbred mice
Authors: Festing Michael F. W. , Roderick Thomas H.
Published: September 2009

Genetic and morphometric distances between 12 inbred strains of mice ranging from closely related substrains to a sub-species were estimated using published data on single locus polymorphisms, and on the basis of up to 44 measurements on seven different bones, respectively. Simulation was also used to investigate sampling effects for the single loci. There were strong and statistically highly significant correlations among all measures of genetic distance ranging from 0·58 for the comparison of single loci with the logarithm of the Mahalanobis distance based on 24 measurements on four bones, to 0·72 for estimates of genetic distance based on single loci and the morphology of the mandible. These findings are in sharp contrast with those of Wayne & O'Brien (1986) who claimed that ‘structural gene and morphometric variation of mandible traits are uncoupled between mouse strains’. Their failure to find such a correlation is probably because their sample of inbred strains included only a single pair of closely related substrains, and no substrains separated for less than 40 years, and because they failed to correct for non-linearity between morphometric and single-locus measurement scales. Simulations and regression analysis suggested that genetic distances could be estimated with approximately equal precision using morphological data on bone measurements or about 10 cladistically informative single loci, which would usually involve sampling about 50 loci. Data based on single-gene markers is usually more informative than morphometric data for studying the similarity of independently-derived strains. However, similarities among closely related populations such as sublines of an inbred strain can usually be studied more efficiently using morphometry.
Effects of identity disequilibrium and linkage on quantitative variation in finite populations
Authors: Tachida Hidenori , Cockerham C. Clark
Published: September 2009

Identity disequilibrium, ID, is the difference between joint identity by descent and the product of the separate probabilities of identity by descent for two loci. The effects of ID on the additive by additive (a * a) epistatic variance and joint dominance component between populations and in the additive, dominance and a * a variance within populations, including the effects on covariances of relatives within populations, were studied for finite monoecious populations. The effects are formulated in terms of three additive partitions, ηb, ηa and ηd of the total ID, each of which increases from zero to a maximum at some generation dependent upon linkage and population size and decreases thereafter. ηd is about four times the magnitude of the other two but none is of any consequence except for tight linkage and very small populations. For single-generation bottleneck populations only d is not zero. With random mating of expanded populations ηb remains constant and ηa and ηd go to zero at a rate dependent upon linkage, very fast with free recombination. The contributions of joint dominance to the genetic components of variance within and between populations are entirely a function of the η's while those of a * a variance to the components are functions mainly of the coancestry coefficient and only modified by the η's. The contributions of both to the covariances of half-sibs, full-sibs and parent-offspring follow the pattern expected from their contributions to the genetic components of variance within populations except for minor terms which most likely are of little importance.
The influence of the Robertsonian translocation Rb(X.2)2Ad on anaphase I non-disjunction in male laboratory mice
Authors: Adler I.-D. , Johannisson R. , Winking H.
Published: September 2009

A Robertsonian translocation in the mouse between theXchromosome and chromosome 2 is described. The male and female carriers of the Rb(X.2)2Ad were fertile. A homozygous/hemizygous line was maintained. The influence of theX-autosomal Robertsonian translocation on anaphase I non-disjunction in male mice was studied by chromosome counts in cells at metaphase II of meoisis and by assessment of aneuploid progeny. The results conclusively show that the inclusion of Rb2Ad in the male genome induces non-disjunction at the first meoitic division. In second metaphase cells the frequency of sex-chromosomal aneuploidy was 10·8%, and secondary spermatocytes containing two or no sex chromosome were equally frequent. The Rb2Ad males sired 3·9% sex-chromosome aneuploid progeny. The difference in aneuploidy frequencies in the germ cells and among the progeny suggests that the viability of XO and XXY individuals is reduced. The pairing configurations of chromosomes 2, Rb2Ad andYwere studied during meiotic prophase by light and electron microscopy. Trivalent pairing was seen in all well spread nuclei. Complete pairing of the acrocentric autosome 2 with the corresponding segment of the Rb2Ad chromosome was only seen in 3·2% of the cells analysed in the electron microscope. The pairing between theXand theYchromosome in the Rb2Ad males corresponded to that in males with normal karyotype. Reasons for sex-chromosomal non-disjunction despite the normal pairing pattern between the sex chromosomes may be seen in the terminal chiasma location coupled with the asynchronous separation of the sex chromosomes and the autosomes. The Rb2Ad chromosome can be useful for studies ofXinactivation, as a marker for parental derivation of theXchromosome and for mapping loci byin situhybridization.
Genetic studies on nucleolus organizer regions (NORs) in cattle
Authors: Mayr B. , Gruber K. , Brem G. , Mayrhofer G.
Published: September 2009

Experimentally produced monozygotic twins, natural opposite sex blood chimeras (freemartins), and several pedigrees were used to evaluate the genetic influences on the nucleolus organizer region (NOR) patterns in cattle. In monozygotic twins, the NOR patterns of both twins are extremely similar. In chimeras, NOR patterns of genetically identical, peripheral blood lymphocytes (PBL) from the two partners resemble each other. In contrast, genetically different PBL (sib organ) differ significantly in the same environment. A high heritability of the individual NOR patterns is also demonstrated in our 23 pedigrees. In conclusion, our data demonstrate that variation in NOR expression is predominantly due to genetic factors.
Analysis of lines of mice selected for fat content. 1. Correlated responses in the activities of NADPH-generating enzymes.
Authors: Asante Emmanuel A. , Hill William G. , Bulfield Grahame
Published: September 2009

Estimates of the activities (Vmax) of four enzymes that generate the coenzyme NADPH, an absolute requirement for tissue fatty-acid synthesis, and of the concentration of NADP plus NADPH were made in lines of mice differing in fat content. These lines had been selected from the same base population for 20 generations, and 3 high, 3 low replicates and 1 unselected control were used. Analyses were performed on liver and gonadal fat pad (GFP) of males at 5 and 10 weeks of age. In both the liver and the GFP, measurable activities of the four enzymes: glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), isocitrate dehydrogenase (IDH) and malic enzyme (ME) expressed per mg soluble protein were, with minor exceptions, higher in the Fat (F) than in the Lean (L) lines at both ages; the highest ratio being 2–2 for ME in the GFP. The relationships between these measurable activities (Vmax) andin vivolipogenesis are not however known. When expressed per gram tissue, the ratios for F to L in the GFP were less than 1 in most cases, presumably because of the very different adipocyte numbers and/or sizes between the lines. There were no significant differences between the lines in the concentration of NADP plus NADPH per gram tissue in liver or GFP, suggesting that F lines converted NADP to NADPH faster than L lines. It is predicted that selection on the enzyme activities would be less efficient than direct selection at changing fat content.
Reconstruction of allopolyploid Brassicas through non-homologous recombination: introgression of resistance to pod shatter inBrassica napus
Authors: Prakash Shyam , Chopra V. L.
Published: September 2009

Pod shattering of rapeseed (Brassica napus) causes serious yield loss. Genetic resistance to shattering has been introgressed intoB. napusfromB. juncea. This followed from allosyndetic pairing between chromosomes of B and C genomes in the interspecific F1 hybrid,B. juncea×B. napus(2n= 37, AABC). The reconstitutedB. napusplant showed regular meiosis with 19 bivalents and had pollen and seed fertility of 84 and 23% respectively. An approach is suggested for achieving introgression from monogenomic diploids to digenomic allopolyploids that exploits non-homologous recombination.
Are responses to artificial selection for reproductive fitness characters consistently asymmetrical?
Authors: Frankham R.
Published: September 2009

Non-linear offspring-parent regressions and heritabilities are expected for characters showing genetic asymmetry due to directional dominance and/or asymmetrical gene frequencies. Since reproductive fitness characters exhibit these characteristics, they should show consistently nonlinear heritabilities, with greater heritabilities in the direction of lower fitness. As a consequence, responses to bi-directional selection on fitness traits should be asymmetrical in the same direction. This prediction has been tested by an analysis of published bi-directional selection experiments for reproductive fitness traits. Significant asymmetry (24 of 30 studies) in the predicted direction was found. For studies reporting realized heritabilities, the means were 0·173 and 0·259 for lines selected for higher and lower reproductive fitness, respectively, the high lines being 33% less than the low lines. Asymmetry was evident for studies reporting realized heritabilities and for those with random mating controls of the same size as the selection lines. Consequently, it is argued that the asymmetry results from genetic asymmetries. This asymmetry has important implications in the improvement of reproductive fitness traits in plant and animal breeding.
Time-dependent changes in gene conversion inAscobolus immersus
Authors: Helmi Shacker , Lamb Bernard C.
Published: September 2009

The stability of conversion frequencies with time was investigated inAscobolus immersus. There were usually marked reductions in gene conversion frequencies at locuswlas crosses matured, to about one third of the initial values. This applied to all sixwlalleles tested, irrespective of their molecular nature, and at all temperatures used. Asci dehiscing early from an apothecium had much higher conversion frequencies than those dehiscing late, but there were no differences between apothecia maturing at different times within a cross. Alleles at four loci unlinked towlwere also tested. All four showed significant changes, though not in all crosses; three loci showed decreases in conversion frequency with time, while one showed an increase. The relative frequencies of different conversion classes often changed with time. These changes appear to result from alterations in locus-specific recombination initiation and in repair of base mispairs in hybrid DNA, not from differential maturation rates of different ascal segregation classes. These effects could cause misinterpretation of quantitative tests of recombination models from gene conversion data.
A mutation resulting in increased triosephosphate isomerase activity inMus musculus
Authors: Merkle Siegbert , Reitmeir Peter , Pretsch Walter
Published: September 2009

A mutation resulting in increased triosephosphate isomerase (TPI) activity in blood was recovered in offspring of procarbazine hydrochloride-treated male mice. Breeding experiments indicated a codominant mode of expression. Compared to the wild type, heterozygous and homozygous mutants have mean erythrocyte TPI activities of approximately 140 and 190%, respectively. Besides blood and erythrocytes the increased activity is expressed to a similar degree in spleen, and to a lesser degree in liver, lung, kidney, muscle and brain. Enhanced activity was absent in the heart. Heterozygous and homozygous mutants are viable, fully fertile and exhibit no significant differences in haematological or other physiological traits studied. Biochemical investigations of TPI in both mutant genotypes revealed neither physicochemical nor kinetic differences compared to the wild type. Moreover, immunoinactivation studies showed no difference in the amount of antiplasma required to inactivate a constant amount of TPI activity in all three genotypes, strongly suggesting that the differences in enzyme activity are attributable to differing amounts of enzyme protein expressed per cell. Mapping studies indicated that the mutation is closely linked to theGapdlocus and consequently is located either adjacent to or within theTpi-1structural locus. It is hypothesized that the mutation affected a regulatory element contiguous to theTpi-1structural locus which acts by increasing the amount of TPI expressed.
Nucleolus organizer-suppressed position-effect variegation inDrosophila melanogaster
Authors: Spofford Janice B. , DeSalle Rob
Published: September 2009

Thewhitelocus is inactivated in a cell-by-cell variegated pattern when juxtaposed with the proximal or distal parts of the nucleolus organizer region (NO) by X chromosome inversion. Recombinants for two such inversions,wm51bandwm4, were obtained and randomized for genetic background.Whitelocus activity was much higher in thewm4recombinant duplicated for most of theNOand much lower in thewm51brecombinant deficient for it. Although there may be other molecular differences between the heterochromatic regions of the recombinants, the most obvious is the dosage ofNO.Suppression of aNOregion-evoked variegated phenotype by additionalNOdoses is discussed in relation to four different classes of models for position-effect variegation (PEV): chromatin structure, nuclear geometry, incomplete transposition of mobile elements, and heterochromatin promoter-driven transcription. A corollary of the structural model is functional subdivision of heterochromatin, which would enable the use of PEV as a tool for its study.
Population genetics of the Y chromosome ofDrosophila melanogaster: rDNA variation and phenotypic correlates
Authors: Clark Andrew G. , Szumski Frances M. , Lyckegaard Eva M. S.
Published: September 2009

One means of examining the evolutionary significance of molecular variation on the Y chromosome is to identify phenotypes specifically affected by Y-linked genes, and to quantify the phenotypic variation and its correlation to the molecular variation. The functional importance of the Y-linked array of rRNA genes is demonstrated by the ability of Y chromosome to rescue X-linkedbobbedlethal alleles, whose lethality is seen in homozygous females. Because low numbers of X-linked rDNA gene copies result in increased developmental time and shortened bristles, and because there is considerable natural variation in Y-linked copy number, a careful examination of Y-linked variation in these two traits may uncover a mode of selection acting on the multigene family. In this study, 36 Y-chromosome replacement lines were tested to detect subtle variation in bristle phenotypes and developmental rates. Correlations among these traits, rDNA gene copy number, and intergenic sequence length were quantified. The absence of significant correlations between phenotypic characters and rDNA copy number or intergenic sequence length suggests that the extant molecular variation in Y-linked rDNA can have at most very small selective effects.
Effect of ecd1 mutation on the expression of genes mapped at the Drosophila melanogaster 3C11-12 intermoult puff
Authors: Furia Maria , D'avino Pier Paolo , Digilio Filomena A. , Crispi Stefania , Giordano Ennio , Polito Lino C.
Published: September 2009

The Drosophila melanogasterecd1 mutation causes a severe temperature-sensitive deficiency in the titre of the steroid hormone eedysone. This mutation was used to investigate the role of eedysone in both the transcription of the genes mapped at the 3C11–12 intermoult puff region and the puff formation. Thoroughly synchronized ecd1 larvae were shifted to the non-permissive temperature at various times of the development; after 24 or 48 h, the levels of the transcripts derived from Sgs-4, Pig-1 and ng-1, the three genes located at the 3C11–12 polytene bands, were determined. The results showed that the levels of the transcripts encoded by Pig-1 and ng-1 are unaffected by the drop in the ecdysone titre occurring in non-permissive conditions whereas the amount of Sgs-4 mRNA is greatly reduced. These data clearly indicate that transcription of the three genes mapped within the puff region is affected differently by the hormone. Furthermore, ecd1 larvae cultured at the non-permissive temperature show a prominent puff at the 3C11–12 polytene bands, indicating that eedysone is not essential for puff induction and that puff size is not simply correlated with high-level Sgs-4 transcription.
The effect of linkage and population size on inbreeding depression due to mutational load
Authors: Charlesworth D. , Morgan M. T. , Charlesworth B.
Published: September 2009

Using a stochastic model of a finite population in which there is mutation to partially recessive detrimental alleles at many loci, we study the effects of population size and linkage between the loci on the population mean fitness and inbreeding depression values. Although linkage between the selected loci decreases the amount of inbreeding depression, neither population size nor recombination rate have strong effects on these quantities, unless extremely small values are assumed. We also investigate how partial linkage between the loci that determine fitness affects the invasion of populations by alleles at a modifier locus that controls the selfing rate. In most of the cases studied, the direction of selection on modifiers was consistent with that found in our previous deterministic calculations. However, there was some evidence that linkage between the modifier locus and the selected loci makes outcrossing less likely to evolve; more losses of alleles promoting outcrossing occurred in runs with linkage than in runs with free recombination. We also studied the fate of neutral alleles introduced into populations carrying detrimental mutations. The times to loss of neutral alleles introduced at low frequency were shorter than those predicted for alleles in the absence of selected loci, taking into account the reduction of the effective population size due to inbreeding. Previous studies have been confined to outbreeding populations, and to alleles at frequencies close to one-half, and have found an effect in the opposite direction. It therefore appears that associations between neutral and selected loci may produce effects that differ according to the initial frequencies of the neutral alleles.
Mapping and characterization of a ‘speciation gene’ inDrosophila
Authors: Orr H. Allen
Published: September 2009

Almost nothing is known about the identity of the genes causing reproductive isolation between species. As a first step towards molecular isolation of a ‘speciation gene’, I mapped and partly characterized a gene causing hybrid male sterility inDrosophila. This analysis shows that sterility ofD. melanogastermales who carry the ‘dot’ fourth chromosome fromD. simulansis due entirely to a very small region of theD. simulanschromosome (including only about 5 salivary gland bands or approximately 250 kb of DNA). Thus the hybrid sterility effect of theD. simulansfourth chromosome is almost surely due to a single gene of very large effect (here namedhms, hybrid male sterile).Hmsis zygotically acting, and theD. simulansallele ofhmsis completely recessive. Furthermore, complementation tests suggest thathmsis not an allele of any known locus inD. melanogaster.
Further observation of paternal transmission ofDrosophilamitochondrial DNA by PCR selective amplification method
Authors: Kondo Rumi , Matsuura Etsuko T. , Chigusa Sadao I.
Published: September 2009

By designing 3′ ends of primers in PCR (polymerase chain reaction), a specific DNA fragment was selectively amplified in the presence of a 103-fold excess of highly homologous (sequence differenceca.2 %) opponent DNA. This technique was applied in detecting paternal leakage of mitochondrial DNA (mtDNA) in intraspecific crosses ofDrosophila simulansand interspecific crosses ofDrosophila simulansandDrosophila mauritiana. The mtDNA types of their progeny were analysed by selective amplification of the paternal mtDNA fragment possessing a polymorphic restriction site and detecting its cleaved fragments. Paternal mtDNA was detected in the progeny of 14 out of 16 crosses. The present result indicates small but frequent inheritance of sperm mtDNA inDrosophila, which is supportive to our previous finding.
Regulation of fitness in yeast overexpressing glycolytic enzymes: responses to heat shock and nitrogen starvation
Authors: Rosenzweig R. F.
Published: September 2009

Current models based on the analysis of linear metabolic pathways at steady-state predict that large increases over wild type in the activity of one enzyme will not alter an organism's fitness. This prediction is tested at steps in a highly branched pathway under two conditions known to alter steady-state: heat shock and nitrogen starvation.Saccharomyces cerevisiaetransformants overproducing 1 of 4 enzymes in glycolysis (hexokinase B, phosphoglucose isomerase, phosphofructokinase, or pyruvate kinase) were subjected to heat shock in both exponential and stationary phases of growth. In neither phase does enzyme overexpression alter heat shock sensitivity. When starved for nitrogen in acetate medium, transformants overproducing hexokinase, phosphoglucose isomerase, and phosphofructokinase sporulate at the same rate and with the same frequency as cells harbouring only the plasmid vector. Current models therefore correctly predict the relationship between activity and components of fitness for 3 of 4 enzymes. By contrast, cells overexpressing pyruvate kinase sporulate poorly. This defect is not observed among cells transformed with a plasmid containing a Tn5 disrupted copy of thePYKgene. These findings are consistent with reports that implicate thePYKlocus in yeast cell cycle control and suggest that it may be challenging to model relations between fitness and activity for multifunctional proteins.
A particular P-element insertion is correlated to the P-induced hybrid dysgenesis repression inDrosophila melanogaster
Authors: Higuet Dominique , Anxolabéhére Dominique , Nouaud Danielle
Published: September 2009

Transposable P elements inDrosophila melanogastercause hybrid dysgenesis if their mobility is not repressed. The ability to regulate the dysgenic activity of the P elements depends on several mechanisms, one of which hypothesized that a particular deleted P element (the KP element) results in a non-susceptibility which is biparentally transmitted. In this study totally nonsusceptible lines, and susceptible lines containing exclusively KP elements (IINS2 line and IIS2 line) were isolated from a M' strain. We show that non-susceptibility is correlated with a particular insertion of one KP element located at the cytological site 47D1. The repression ability of the GD sterility is determined by a recessive chromosomal factor, and cannot be due to the KP-element number. Here the repression of the P mobility is associated with reduction of the P transcripts and the inhibition of P promoter activity.
Comparative evolution of P–M system and infection by the sigma virus in French and Spanish populations ofDrosophila melanogaster
Authors: Fleuriet Annie , Kalmes Robert , Pascual Luis , Periquet Georges
Published: September 2009

In 1983, an extensive survey of populations ofD. melanogasterwas started in a southern French region (Languedoc) in two non-Mendelian systems: the P–M system of transposable elements and the hereditary Rhabdovirus sigma. Unexpectedly fast-evolving phenomena were observed and interesting correlations were noted, giving similar geographical pattern to the region in both systems. For these reasons, the analysis was continued and extended towards the north (Rhône Valley) and the south (Spain). In the P–M system, all the Languedoc populations evolved from 1983 to 1991 towards the Q type which is characteristic of the Rhône Valley populations. In contrast, M′ strains are currently observed in the southernmost French populations and in all Spanish ones, so that there is a clear pattern in their geographical distribution.

The frequency of flies infected by the sigma virus dramatically increased from 1983 to 1988 in Languedoc; this increase was clearly correlated with some viral characteristics. But, in northern France, similar characteristics did not trigger any increase in the frequency of infected flies. The data presented here show that the distinctive features of Languedoc extend northwards through the Rhone Valley up to Lyon and disappears southwards before the Spanish border.
Chromosome interactions in P-M dysgenic male recombination ofDrosophila melanogaster
Authors: Eggleston P. , Exley K. A.
Published: September 2009

The frequency, distribution and structure of P elements on the second and third chromosomes of Texas 1, a wild-type inbred strain ofDrosophila melanogaster, were investigated byin situhybridization. These autosomes were isolated individually and used as P-element donors to study the frequency and distribution of male recombination events generated on recipient chromosomes which were originally devoid of P sequences. The P-element array of chromosome 2 was shown to generate higher male recombination frequencies on chromosome 3 than vice versa, despite having fewer P factors and fewer P elements in general. This is likely to be due to the presence and distribution of specific P-deletion derivatives, which vary in their ability to repress P mobility. The male recombination generated on recipient chromosomes is associated with the insertion of donated P sequences, but only in a small minority of cases could a novel P-element site be detected at, or near, the recombination breakpoint. The majority of such breakpoints appear to be associated either with unsuccessful P insertion, or with the action of P transposase attracted by P elements newly inserted elsewhere on the recipient chromosome. Recent evidence also suggests that a small proportion of the breakpoints may be associated with the action of P transposase alone. Male recombination breakpoints appear to be distributed effectively at random along the recipient autosomes, and their frequency of occurrence was shown to correlate with the physical length of DNA available between markers, as revealed by the polytene map distance.
The time of detection of recessive visible genes with non-random mating
Authors: Caballero Armando , Etheridge Alison M. , Hill William G.
Published: September 2009

Expressions for the probability and average time of detection of a recessive visible gene in populations where there is partial selfing or partial full-sib mating are presented. A small increase in the proportion of inbred matings greatly reduces the average time until detection and increases the proportion detected. Unless the proportion of inbred matings or the population size is very small, the time and proportion detected are approximately independent of the population size.
A deleted hobo element is involved in the unstable thermosensitive vgal mutation at the vestigial locus in Drosophila melanogaster
Authors: Bazin C. , Williams J. , Bell J. , Silber J.
Published: September 2009

We have described a new unstable mutant of the vestigial locus isolated from a natural population. From this mutant, vestigialalmost (vgal), wild-type (vgal+), and extreme (vgext), alleles arose spontaneously. The molecular analysis of vgal shows that the mutation is due to a 1874 bp hobo element inserted in a vestigial intron. Two distinct kinds of events lead a wild-type phenotype. Three independent vgal+ alleles result from an excision of the hobo element and two other vgal+ alleles have further deletions of hobo sequence. The sequence of one of them shows a 1516 bp hobo insertion at the same place and in the same orientation as the 1874 bp insertion. In the vgext alleles, we found a 5′ or 3′ variably sized deletion of vg sequences. One of them, which has been cloned and sequenced, has a deletion finishing exactly at the left terminal repeat′ hobo element. The genetic implications of these different genetic structures are discussed.
Identification of ornithine decarboxylase as a trait gene for growth in replicated mouse lines divergently selected for lean body mass
Authors: Gray A. , Tait A.
Published: September 2009

Studies of lines of mice selected for body mass have shown that there is a significant genetic component affecting this trait although the nature of the genes involved remains to be elucidated. Using replicate lines of mice, our studies have shown that two different variants of the mouse ornithine decarboxylase (ODCase) gene have been selected in replicate lines of mice selected for high and low lean body mass respectively. One variant is associated with an increased peak of ODCase activity in embryos (10–13 days of gestation) in all high mass lines and with a restriction fragment length polymorphism of the expressed gene. The increased ODCase activity coincides with increased ODCase mRNA levels in the high mass selected lines. These results provide evidence implicating ornithine decarboxylase as a major factor in cell growth, and as a candidate ‘trait gene’.
Linkage disequilibrium in thewhitelocus region ofDrosophila melanogaster
Authors: Miyashita Naohiko T. , Aguadé Montserrat , Langley Charles H.
Published: September 2009

Linkage disequilibrium between molecular polymorphisms in a 10 kb region in thewhitelocus ofDrosophila melanogaster, revealed with a battery of four-cutter restriction enzymes, was investigated in 266 lines sampled from seven natural populations around the world. A total of 73 (35 restriction site, 37 insertion/deletion and 1 inversion) polymorphisms were detected, of which 55 non-unique polymorphisms were analysed for linkage disequilibrium. Clustering of significant linkage disequilibrium was observed in the transcriptional unit of thewhitelocus as in Miyashita & Langley (1988). It was shown that about two thirds of the 2-locus combinations showing significant linkage disequilibrium have similar degree and direction of association over different populations. Despite lower divergence in allelic frequencies of molecular polymorphisms among populations, an increase in the proportion of 2-locus pairs showing significant linkage disequilibrium is observed in the transcriptional unit. Large values of Ohta'sDmeasure ratio (1982a, b) cluster in the transcriptional unit, and correspond to significant linkage disequilibria. Although the exact molecular mechanism is not clear, these results suggest that epistatic selection is responsible for significant linkage disequilibrium in the transcriptional unit of this locus
The genetic basis of response in mouse lines divergently selected for body weight or fat content. I. The relative contributions of autosomal and sex-linked genes
Authors: Hastings Ian M. , Veerkamp Roel F.
Published: September 2009

Lines of mice have been divergently selected for over forty generations on either body weight or fat content. Reciprocal crosses were made between the divergent lines and the offspring backcrossed to the parental lines. The resulting data allowed us to investigate the genetic basis of response, including two features of particular interest: (i) the relative contribution of autosomal and sex-linked genes and whether any significant Y chromosome or cytoplasmic effects were present (ii) the mechanism of gene action, whether predominantly additive or whether significant dominance effects were present. A large additive sex-linked effect was observed in lines selected on body weight which accounted for approximately 25% of the divergence. The remaining 75% of the divergence appeared to be autosomal. There was no apparent sex-linked effect in lines selected on fat content and the response appeared to be entirely autosomal and additive.
Genotypically unbalanced diploid ↔ diploid foetal mouse chimaeras: possible relevance to human confined mosaicism
Authors: West John D. , Flockhart Jean H.
Published: September 2009

Two series of mouse chimaeras were produced by aggregating pairs of eight-cell embryos that differed at theGpi-1slocus, encoding glucose phosphate isomerase (GPI-1); the paired embryos were respectively homozygousGpi-1sa/Gpi-1saandGpi-1sb/Gpi-1sb. Chimaeric blastocysts were transferred to pseudopregnant females, that were homozygousGpi-1se/Gpi-1seand produced only GPI-1 C enzyme. Quantitative electrophoresis of GPI-1 was used to estimate the contribution of each embryo (GPI-1 A and GPI-1B enzyme activity) to the foetus, placenta and other extraembryonic tissues of 12½ day chimaericconceptuses. For both series of chimaeras, the distributions of %GPI-1A in different tissues were classified as (1) balanced and typical, (2) balanced but atypical or (3) unbalanced. One series of chimaeras was clearly unbalanced, so that the cells derived from the (C57BL × CBA/Ca)F2embryo (Gpi-1sb/Gpi-1sb) predominated over those derived from the BALB/c inbred strain (Gpi-1sa/Gpi-1sa) in most foetuses. Two significant observations were made concerning this unbalanced series. Firstly, the mean composition of the placenta and other extraembryonic tissues was similar to that in the foetus i.e. also unbalanced with (C57BL × CBA/Ca)F2(abbreviated to BF2) cells predominating. Secondly, despite this generalizeddeficiency of BALB/c cells, there were differences in the frequency of non-chimaeric tissues between different developmental lineages. In 20/34 chimaeric conceptuses in the unbalanced series only BF2cells were detected in the foetus, whereas both BF2and BALB/c cells were present in at least one of the extraembryonic tissues. This group of chimaeras, therefore, shows some similarities to human confined mosaicism. Although chimaerism occurred more often in the primitive endoderm (hypoblast) lineage (yolk sac endoderm and parietal endoderm) than in the placenta, this may also be the case in human mosaics. The mosaic status of the human yolk sac endoderm is usually unknown so it is possible that mosaicism often occurs in the yolk sac endoderm as well as the trophectoderm in human ‘confined placental mosaicism’. The uniformly unbalanced phenotype seen in the mouse chimaeras may be a result of generalized cell selection against BALB/c cells in all tissues. As an alternative explanation, we propose that most of the BALB/c cells in the blastocyst are allocated to the mural trophectoderm, which has a limited mitotic potential and so contributes little to the mid-gestation conceptus. Further work is required to test these possibilities.
Polymorphism and linkage analysis of the prothoracicotropic hormone gene in the silkmoth,Bombyx mori
Authors: Shimada Toru , Hasegawa Tsuyoshi , Matsumoto Kayoko , Agui Noriaki , Kobayashi Masahiko
Published: September 2009

We looked for polymorphism of the prothoracicotropic hormone gene locus (Ptth) among inbred strains of the silkmoth,Bombyx mori, by invitroDNA amplification (polymerase chain reaction), and found three alleles,PtthA,PtthBandPtthC. ThePtthAallele contained a third intron consisting of 680 bp and a fourth intron of 350 bp.PtthBcontained the same size third intron but a longer fourth intron of 490 bp, while Ptthc had a longer third intron of 1080 bp and a shorter fourth intron of 350 bp. In 29 strains which we examined, 9 strains hadPtthA, 8 strains hadPtthB, and 2 strains had Ptthc. The other 10 strains had heterogeneous genotypes with the same 3 alleles.
IR hybrid dysgenesis increases the frequency of recombination inDrosophila melanogaster
Authors: Chaboissier Marie-Christine , Lemeunier Françoise , Bucheton Alain
Published: September 2009

The I factor is a LINE-like transposable element responsible for the I-R system of hybrid dysgenesis inDrosophila melanogaster. Inducer strains of this species contain several I factors whereas reactive strains do not. I factors are stable in inducer strains, but transpose at high frequency in the germ-line of females, known as SF females, produced by crossing reactive females and inducer males. Various abnormalities occur in SF females, most of which result from this high rate of transposition. We report here that recombination is increased in the germ-line of these females. This is a new characteristic of the I-R system of hybrid dysgenesis that might also be associated with transposition of the I factor.
Recent evolution of mousethaplotypes at polymorphic microsatellites associated with thetcomplex responder (Tcr) locus
Authors: Ardlie Kristin G. , Silver Lee M.
Published: September 2009

Microsatellites closely associated with each member of theTcp1Ogene family were amplified simultaneously fromthaplotype and wild-type forms of mouse chromosome 17, by PCR. Thetcomplex responder (Tcr) locus, which plays a central role in transmission ratio distortion, maps within theTcp10cluster on thethaplotype. Thus the amplified set of microsatellite loci (referred to collectively asTcp10ms) provides a direct marker for this central component of the meiotic drive system associated with all naturally occurringthaplotypes. A uniqueTcp10mspattern of microsatellite alleles was obtained for a number of independent, laboratory-maintained complete and partialthaplotypes. Independenttchromosomes found in wild mice from US populations also had unique patterns, even when they were classified within the same lethal complementation group. Wild and laboratory chromosomes in thetw5group showed similarly-sized but non-identical Tcp10ms patterns, suggesting they share a recent common ancestor. These chromosomes are likely to have derived from an ancestral chromosome within the founding population of North American house mice. The Tcp10ms pattern was also shown to be useful in field studies for distinguishing among independentthaplotypes, when more than one is present within a single population.
Models for mapping quantitative trait loci (QTL) in progeny of non-inbred parents and their behaviour in presence of distorted segregation ratios
Authors: Schäfer-Pregl R. , Salamini F. , Gebhardt C.
Published: September 2009

In plants, models for mapping quantitative trait loci (QTL) based on flanking markers have been mainly developed for progenies of inbred lines. We propose twoflanking marker models for QTL mapping in F1progenies of non-inbred parents. The first is based on the segregation of four different scorable alleles at a marker locus (the four-allele model) and the second (the commonallele model) on one scorable allele per marker locus segregating in both parents. These models are suitable for the majority of the allelic configurations which may occur in crosses between heterozygous parents. For both cases, when four scorable or one common-allele per marker locus segregate, additional algorithms were developed to estimate the recombination frequency between two marker loci. Tests carried out with simulated populations of various sizes indicate that the models provide a good estimate of QTL genotypic means and of recombination frequencies between flanking markers and between the marker loci and the QTL.The estimates of QTL genotypic means have a higher precision than the estimates of recombination frequencies. The four-allele model shows a higher ability to detect QTLs than the common-allele model. If segregation ratios are distorted, the power of both models and the precision of the estimates of recombination frequencies are reduced, whereas the accuracy of estimates of QTL genotype means is not affected by distorted segregation ratios. The power of the common-allele model is substantially reduced if QTL genotypic means depend on additive allelic interactions, whereas the four-allele model is less affected by the non-additive behaviour of QTL alleles.
Natural Repressors of P-induced hybrid dysgenesis inDrosophila melanogaster: a model for repressor evolution
Authors: Corish P. , Black D. M. , Featherston D. W. , Merriam J. , Dover G. A.
Published: September 2009

Type I repressors control P element transposition and comprise full length elements and elements with small 3′ deletions in the final exon. Using a sensitive assay for measuring the strength of repression of P element transposition in somatic and germline tissues, we have isolated and characterized a naturally occurring type I repressor element from a Q population ofDrosophila melanogaster. We demonstrate that the almost complete repression of transposition in this population is a mixture of KP elements with intermediate levels of repression, and the strong contribution of a single 2·6 kb P element deletion derivative, which we call SR (Strong Repressor). A deletion in the final intron of SR allows for the constitutive production of a putative 75 kDa repressor protein in germline tissues in addition to the production of the 66 kDa repressor in the soma, which would result in a biparental mode of inheritance of repression. Basedon the four observed classes of natural Q populations, we propose a model in which populations containing SR-like elements, capable of producing strong type I repressor constitutively, have a selective advantage over populations which rely either on maternally transmitted P cytotype or on KPinduced weak levels of repression. Such populations may subsequently spread and constitute an evolutionary stable strategy for the repression of hybrid dysgenesis inDrosophila melanogaster.
A quantitative test for developmental neutrality of a transgenic lineage marker in mouse chimaeras
Authors: West John D. , Keighren Margaret A. , Flockhart Jean H.
Published: September 2009

The mouse transgene, provisionally designated TgN(Hbb-b1)83Clo, was produced by Dr C. Lo by pronuclear injection of the cloned ß-major globin gene and comprises a highly reiterated sequence that is readily detected by DNAin situhybridization on histological sections. This fulfils many of the requirements of an ideal genetic cell marker and has been widely used for lineage studies with mouse chimaeras. However, it is not known whether it causes cell selection or influences developmental processes, such as cell mixing, in chimaeric tissues. In the present study, nontransgenic genetic markers (electrophoretic polymorphisms of glucose phosphate isomerase and differences in eye pigmentation) revealed no significant effect of the presence of hemizygous transgenic cells on the overall composition, size or gross morphology of 12½ d chimaeric foetuses, placentas or extraembryonic membranes. Also, a previously described maternal genetic effect on the composition of chimaeric tissues occurred in the presence or absence of the transgene. These tests have demonstrated that hemizygous cells are not at a significant selective disadvantage, when incorporated into mouse aggregationchimaeras with non-transgenic cells. Further studies are needed to test whether homozygous transgenic cells are also selectively neutral and to test whether hemizygous or homozygous transgenic cells influence developmental processes, such as cell mixing, that were not tested.
Behavioural changes as a correlated response to selection
Authors: Holmes Ingrid S. , Hastings Ian M.
Published: September 2009

Lines of mice have been selected for up to 50 generations on the following traits: high body weight, low body weight, high fat content or low fat content. The lines selected for high or low body weight differ by a factor of 2·5 and those selected for high or low fat content differ by a factor of five, both traits measured in 10 week old males. A set of behavioural traits was measured to ascertain whether this selection had caused correlated responses in behaviour: studies included feeding behaviour, open field behaviour, ultrasound calling rates of pups, and the response to the introduction of a novel physical object. Alterations in behavioural patterns which were expecteda prioriwere observed but there appeared to be no changes in behaviour associated with any one selection criterion. Estimates of the genetic correlations between selected and behavioural traits were, with one exception, generally less than 0·1 in magnitude and not significantly different from zero (the exception was food intake in lines selected on body weight). Assuming that mice are accurate models for commercial species, then these results have important implications for animal welfare: they demonstrate that large scale behavioural changes do not arise as an inevitable consequence of intense long-term selection on traits of economic importance in commercial species