bluuebunny/crossref_metadata_2025 huggingface dataset:
Can chromosomal heterosis inDrosophilabe explained by deleterious recessive genes? Negative results from a dichromosomal population test
Authors: Wilton Alan N. , Joseph Michael G. , Sved John A.
Published: September 2009

High levels of chromosomal heterosis have previously been detected inDrosophilausing the balancer chromosome equilibration (BE) technique, in which single wild-type chromosomes are introduced into population cages along with a dominant/lethal balancer chromosome. The balancer chromosome is rarely eliminated in such populations, showing that the fitness of chromosome homozygotes must be low by comparison with chromosomal heterozygotes. As with all cases of chromosomal heterosis, the underlying cause could either be deleterious recessives at various loci or generalized overdominance. The experiment of the present paper examines the first of these explanations. Population cages containing just two wild-type chromosomes (dichromosomal populations) were set up and allowed to run for many generations. Single chromosomes were then re-extracted from these populations, and their fitness measured using the BE technique. Our expectation was that the gradual elimination of recessive genes from the dichromosomal populations ought to result in an increase in the fitness of such re-extracted chromosome homozygotes. Yet in two replicated experiments we were unable to demonstrate an; unequivocal increase in fitness. We have estimated the rate of increase of fitness under multiple locus dominance and partial dominance models. The principal unknown parameter in these calculations is the selection intensity per locus,s. The expected increase is approximately proportional tos, and we estimate that values ofsaround 1/64 should be detectable in our experiments. However linkage is expected to reduce the efficiency of the dichromosomal procedure We show by computer simulation that this reduction is by a factor of approximately 2, thus increasing the detectable level ofsto approximately 1/32. Consideration of mutation-selection balance models shows that this is a feasible selection intensity only if dominance is nearly complete. Thus we are unable to rule out the notion that the genes responsible for heterosis are maintained by a simple mutation-selection balance, but the experimental results constrain the parameters of such a model to a narrow range.
Chromosomal localization of the mouse gene coding for vimentin
Authors: Mattei Marie-Genevieve , Lilienbaum Alain , Lin Li Zhen , Mattei Jean-François , Paulin Denise
Published: September 2009

The chromosomal location of the mouse gene coding for vimentin, one of the intermediate filament subunits, was determined by in situ hybridization using specific H3-labelled DNA probes. There is only one copy of the vimentin gene and it is located on chromosome 2 region A2.
Cytogenetic manifestations associated with the reversion, by gene amplification, at the HGPRT locus in V79 Chinese hamster cells
Authors: Di Leonardo A. , Agnese C. , Cavolina P. , Maddalena A. , Sciandrello G. , Randazzo R.
Published: September 2009

Some HGPRT spontaneous revertants were isolated from a mutant line (E2) of V79 Chinese hamster cells and phenotypically characterized. Dot–Blot hybridization with a32P-Iabelled HGPRT probe revealed an increase in the number of HGPRT sequences in some of these revertants, suggesting the occurrence of gene amplification. Cytogenetic analysis performed in three of these revertants showed a characteristic abnormally banding region (ABR) on the elongated p arm of theXchromosome.In Situhybridization in one revertant (RHE2) showed that the amplified sequences reside on the p+arm of theXchromsome in two different localizations. Because of the very probable clonal origin of the revertant, these features indicate that the amplified sequences might rearrange after their integration into the chromosome.
Interaction of Hairless, Delta, Enhancer of split and Notch genes ofDrosophila melanogasteras expressed in adult morphology
Authors: Siren Mariitta , Portin Petter
Published: September 2009

The interaction of three neurogenic lociviz.Delta, Enhancer of split and Notch, and a related gene, Hairless, ofDrosophila melanogasterwas investigated at the adult morphology level by measuring the effects of the mutations of the three other genes on the expression of the recessive lethal antimorphic Abruptex mutations of the Notch locus. The Abruptex mutations were also coupled incisortranswith facet-glossy or split mutations of the Notch locus. In some of the experiments, the genotype of the fly was homozygous for either facet-glossy or split mutation or their wild type alleles but heterozygous for the Abruptex. Facet-glossy is located in a large intron of the locus, whereas split is located in the same exon as Abruptex. In all compounds studied, Delta suppressed the expression of Abruptex while Hairless and Enhancer of split enhanced it. The interactions of the four genes studied were allele specific, suggesting an interaction at the protein level. The comparison of the results presented in this study on the interaction of the neurogenic genes with other results on the same subject suggests that the interactions are similar in embryonic and imaginal development.
Quantitative genetic variability maintained by mutation-stabilizing selection balance: sampling variation and response to subsequent directional selection
Authors: Keightley Peter D. , Hill William G.
Published: September 2009

A model of genetic variation of a quantitative character subject to the simultaneous effects of mutation, selection and drift is investigated. Predictions are obtained for the variance of the genetic variance among independent lines at equilibrium with stabilizing selection. These indicate that the coefficient of variation of the genetic variance among lines is relatively insensitive to the strength of stabilizing selection on the character. The effects on the genetic variance of a change of mode of selection from stabilizing to directional selection are investigated. This is intended to model directional selection of a character in a sample of individuals from a natural or long-established cage population. The pattern of change of variance from directional selection is strongly influenced by the strengths of selection at individual loci in relation to effective population size before and after the change of regime. Patterns of change of variance and selection responses from Monte Carlo simulation are compared to selection responses observed in experiments. These indicate that changes in variance with directional selection are not very different from those due to drift alone in the experiments, and do not necessarily give information on the presence of stabilizing selection or its strength.
Clonal analysis of thelacoperons fromKlebsiellaM5a1 and the Lac plasmid (pRE2) fromKlebsiellaV9A
Authors: Hitchin F. E. , Reeve E. C. R.
Published: September 2009

The chromosomallacregion of the coliform bacteriumKlebsiellaM5al was cloned into the multicopy plasmid pBR322 to give pHE7 and pHE8. pHE8 contains 12·6 kb of M5al DNA, including its completelacoperon, and pHE7 contains 2·5 kb of M5al DNA and includes the completelac Ygene and a small segment oflacZ. The M5al operon has the same gene order as theEscherichia coli lacoperon. Thelacgenes of the Lac plasmid ofKlebsiellaV9A were cloned into pBR322 to give pHE1 and pHE2, of approximately 39 and 43 kb. Both plasmids were unstable in anE. coli RecA- strain, in contrast to the stability of pHE8. Polyacrylamide gel electrophoresis tests suggested that the M5a1 β-galactosidase monomer is about 5% longer, i.e. has about 50 more amino acids, than that of theE. coli Zgene. Tests made on the enzymes coded by thelacoperons of M5a1, anotherKlebsiellastrain (V9A) and its resident Lac plasmid, and several Lac+Enterobacteria, led to the conclusion that onlyEscherichia coliamong the Enterobacteria contains an activelacAgene.
Characterization of third chromosome dominant α-methyl dopa resistant mutants (Tcr) and their interactions withl(2)amdα-methyl dopa hypersensitive alleles inDrosophila melanogaster
Authors: Bishop Clifton P. , Sherald Allen F. , Wright Theodore R. F.
Published: September 2009

InDrosophila melanogastertwo alleles at theThird chromosome resistancelocus (Tcr; 3–39·6) were isolated in a screen of EMS mutagenized third chromosomes for dominant resistance to dietary α-methyl dopa, α-MD, a structural analogue of DOPA. Both alleles ofTcrare recessive lethals exhibiting partial complementation. Almost half (48·3%) of theTcr40/Tcr45heterozygotes die as embryos but some survive past adult eclosion. Both the embryonic lethal phenotype and the adult phenotype suggest thatTcris involved in cuticle synthesis.Tcrmutants suppress the lethality of partially complementing alleles at the α-MD hypersensitive locus,l(2)amd. The viability ofTcr40/Tcr45, however, is not increased by the presence of al(2)amdallele. The possibility that theTcrandl(2)amdmutations reveal a catecholamine metabolic pathway involved in cuticle structure is discussed.
RelAmutation and pBR322 plasmid amplification in amino acid-starved cells ofEscherichia coli
Authors: Riethdorf Sabine , Schroeter Andreas , Hecker Michael
Published: September 2009

Plasmid pBR322 is amplified following amino-acid limitation inEscherichia coli relAhosts. InrelA+hosts there was no significant amplification or a much smaller one. Plasmid amplification is due to therelAmutation; when therelA+allele is transferred into therelAmutant CP79 this strain no longer amplifies plasmid DNA during amino acid starvation. It is concluded that ppGpp is a negative effector of plasmid replication. Amplification is temperature dependent, being maximal at 32 °C and negligible at 37 °C.
Wsp-1, a set of genes controlling water-soluble proteins in wheat and related species
Authors: Liu C. J. , Chao S. , Gale M. D.
Published: September 2009

Three water-soluble wheat endosperm proteins of the wheat variety Chinese Spring have been shown, by isoelectric focusing, to be the products of genes located on the long arms of chromosomes 7A, 7B and 7D. In the absence of any evidence of function these genes have been assigned the temporary symbol, Wsp-1.

Considerable intervarietal variation was found among a sample of 44 hexaploid wheat varieties. Five alleles at Wsp-A1, three at Wsp-B1 and two at Wsp-D1 were identified. Intrachromosomal mapping showed that Wsp-B1 is located distally on the long arm of chromosome 7B.

Alien homoeoloci were identified on chromosomes 7Hch of Hordeum chilense, 7H of H. vulgare, 7E of Agropyron elongatum, 7S1 of Aegilops sharonensis and 7V of Dasypyrum villosum. Some other loci encoding WSPs found in wheat and some alien species are also briefly described.
Genomic imprinting: normal complementation of murine chromosome 16
Authors: Berger Christoph N. , Epstein Charles J.
Published: September 2009

Parental imprinting effects for chromosome 16 were investigated using disomic animals which were obtained by mating (Rb32Lub × Rb2H) F1 mice. Two allelic forms of the enzyme CuZn-superoxide dismutase, Sod-1a and Sod-1c, were` used to identify maternally or paternally disomic animals. Both types of disomic animals were found with the expected frequencies and did not visibly differ from one another or from non-disomic animals. These results indicate that the genomic imprinting mechanism either does not act on chromosome 16, or, if it does, does not do so in a manner which affects normal development.
Localization of P elements, copy number regulation, and cytotype determination inDrosophila melanogaster
Authors: Biémont C. , Ronsseray S. , Anxolabéhère D. , Izaabel H. , Gautier C.
Published: September 2009

Seventeen highly-inbred lines ofDrosophila melanogasterextracted from an M′ strain (in the P/M system of hybrid dysgenesis) were studied for their cytotype and the number and chromosomal location of complete and defective P elements. While most lines were of M cytotype, three presented a P cytotype (the condition that represses P-element activity) and one was intermediate between M and P. All lines were found to possess K.P elements and only eight to bear full-sized P elements. Only the lines with full-sized P elements showed detectable changes in their P-insertion pattern over generations; their rates of gain and of loss of P-element sites were equal to 0·12 and 0·09 per genome, per generation, respectively. There was no correlation between these two rates within lines, suggesting independent transpositions and excisions in the inbred genomes. The results of both Southern blot analysis andin situhybridization of probes made from left and right sides of the P element strongly suggested the presence of a putative complete P element in region 1A of the X chromosome in the three lines with a P cytotype; the absence of P copy in this 1A region in lines with an M cytotype, favours the hypothesis that the P element inserted in 1A could play a major role in the P-cytotype determination. Insertion of a defective 2 kb P element was also observed in region 93F in 9 of the 13 M lines. The regulation of the P-element copy number in our lines appeared not to be associated with the ratio of full-length and defective P elements.
Direct and correlated responses to artificial selection on lipid and glycogen contents inDrosophila melanogaster
Authors: Clark Andrew G. , Szumski Frances M. , Bell Karen A. , Keith Lisa Esterling , Houtz Sharyn , Merriwether D. Andrew
Published: September 2009

A large outbred population ofDrosophila melanogasterwas subjected to artificial selection on lipid and glycogen storage. In three separate experiments, two replicates underwent sib selection for both increased and decreased storage. In the first study, flies were selected on the basis of total triacylglycerol for ten generations. This experiment resulted in no significant direct response, but there was a significant change in total body weight, underscoring the importance of concern for the allometric relationship between body weight and lipid content. In the second study, selection was performed for 15 generations on the percentage of body composition that was triacylglycerol. A significant direct response was obtained, and the two replicates revealed heritability estimates of 0·40 and 0·43. The third study selected glycogen content for 15 generations, and produced a significant response with heritabilities of 0·25 and 0·31. A series of 12 biochemical and enzyme kinetic traits was examined at five generation intervals in all experiments, and a number of correlated responses were detected. The results are interpreted with respect to the evolutionary constraints on energy storage evolution and the genetic basis of the allometric relationship between body weight and fat content.
Chromosomal fragment responsible for genetic mosaicism in larval body marking of the silkworm,Bombyx mori
Authors: Fujiwara Haruhiko , Ninaki Osamu , Kobayashi Masahiko , Kusuda Jun , Maekawa Hideaki
Published: September 2009

Several genetic mosaics for larval body marking of the silkworm,Bombyx mori, have been induced by X-ray irradiation. It is hypothesized that the occasional loss of chromosomal fragments carrying the genes for body marking during development may give rise to this type of mosaicism. Using pulsed field gel electrophoresis (PFGE), we find that a DNA molecule of about 2·5 megabases (Mb) is present in one type of mosaic (mottled striped strains pSm788 and pSm872), and not in any other strain. This DNA fragment hybridizes strongly with some chorion genes which are less than 6·9 cM away from thepslocus, and hence it corresponds to a chromosomal fragment containing genes for both striped marking (ps) and the chorion. In the non-mottled psstrain, the phenotype before X-ray irradiation, no band was detected either on a PFGE gel or after hybridization with the chorion probe. These results suggest that the mottled psstrains carry short chromosome fragments which are lost differentially during cell divisions.
Gene mapping and cross-resistance in cyclodiene insecticide-resistant Drosophila melanogaster (Mg.).
Authors: Ffrench-Constant R. H. , Roush R. T.
Published: September 2009

Resistance to the cyclodiene insecticide dieldrin maps to a single gene (Rdl) on the left arm of chromosome III in Drosophila melanogaster (Meigen). The gene was further mapped by the use of chromosomal deficiencies to a single letter sub-region, 66F, on the polytene chromosome. The cross-resistance spectrum of a backcrossed strain lacking elevated mixed function oxidase activity, a common resistance mechanism, was examined. Levels of resistance similar to those found in other insects were found to dieldrin, aldrin, endrin, lindane, and picrotoxinin. Strong similarity of this single major gene with that found in other cyclodiene resistant insects is suggested by its cross-resistance spectrum and chromosomal location, via homology with other Diptera. The significance of major genes in insecticide resistance is discussed.
Tich: a mutant causing disproportional growth in the mouse
Authors: Archer James R. , Archer Victoria A. , Festing Michael F. W. , Ghiraldini Mirian A.
Published: September 2009

A spontaneous mutation ‘tich’ (gene symbol tch) appeared as a recessive mutation in inbred mice of strain A. TL. Homozygotes are rather dumpy mice of approximately normal weight but with short limbs and tail. Skeletal measurements on backcross siblings show that the mandible bones are almost normal but long bones and some parts of the pelvic and pectoral girdles are short. Although tich resembles brachypodism phenotypically it is not linked to agouti, and does not match the description of any other skeletal mutation. There was some evidence for weak linkage with albinism on chromosome 7. The mutation has reappeared amongst the A. TL mice of a UK commercial breeder and may have been accepted as the norm for A. TL amongst some European users of this mouse.
Tpi-1andGapdare linked very closely on mouse chromosome 6
Authors: Pretsch Walter , Neuhäuser-Klaus Angelika , Merkle Siegbert
Published: September 2009

Mutations in the structural genes for triosephosphate isomerase and glyceraldehyde-3-phosphate dehydrogenase activity in the mouse, selected after mutagen treatment, were used to estimate the map distance between the two loci. It is shown thatTpi-1 andGapdare closely linked on chromosome 6, with a recombination frequency of 0·1±0·1%.
The effect of H-2 region and genetic background on hormone-induced ovulation rate, puberty, and follicular number in mice
Authors: Spearow J. L. , Erickson R. P. , Edwards T. , Herbon L.
Published: September 2009

We have examined the effects of major histocompatibility (H-2) haplotypes and genetic background (all loci other than the H-2 region) on hormone-induced ovulation rate in congenic strains of mice. In comparison with the H-2a haplotype, the H-2b haplotype increased hormone-induced ovulation rate 92% on the A/J (A) genetic background. However, H-2 haplotype did not affect hormone-induced ovulation rate on the C57BL/10J (C57) genetic background. The H-2b-linked gene(s) increased hormone-induced ovulation rate on the A/J genetic background largely by (1) enhancing the maturation of follicles in response to pregnant mare's serum gonadotrophin (PMSG) and (2) altering the stages of follicular development which can be induced to ovulate in response to human chorionic gonadotrophin (hCG). The observed effects of H-2 on hormone-induced ovulation rate were not explained by differences in the timing of puberty, the number of follicles present in untreated females, or the incidence of follicular atresia. The effect of genetic background on hormone-induced ovulation rate was much greater than was the effect of the H-2 region. We found that hormone-induced ovulation rate was five- to six-fold higher on the C57 genetic background than on the A genetic background. The C57 genetic background increased hormone-induced ovulation rate by (1) enhancing the induction of follicular maturation in response to gonadotropins and (2) by reducing the incidence of follicular atresia.
Mixed model analysis of a selection experiment for food intake in mice
Authors: Meyer K. , Hill W. G.
Published: September 2009

Data from 23 generations of mice selected for increased and reduced appetite were analysed by Restricted Maximum Likelihood fitting an animal model with litters as additional random effects. Traits considered were food intake between 4 and 6 weeks of age adjusted for 4-week body weight (AFI), the selection criterion, and body weight at 6 weeks (6WW). Selection was carried out within families. A high and a low selection line and a control were maintained in each of three replicates. Analyses were performed for each replicate separately taking subsets of the data spanning different numbers of generations. Overall estimates of heritabilities were 0·15 for AFI, which agreed well with realized heritability estimates, and 0·42 for 6WW. The litter variance, expressed as a proportion of the phenotypic variance, was 0·21 for both traits, yielding intraclass correlations of full-sibs of 0·29 and 0·42, respectively. Similar results were obtained for variances of each trait using univariate and multivariate analyses. From the latter, estimates of correlations between the two traits were 0·46 for additive genetic, −0·19 for litter and 0·31 for residual effects, resulting in a phenotypic correlation of 0·23. Analyses of data from generations 2–7, 8–13 and 14–23 separately showed a marked decrease in genetic variance and heritability in later generations for both traits. Heritabilities of AFI, for instance were 0·24, 0·10 and 0·07, respectively. These changes could not be attributed to the effects of inbreeding or of selection in an infinitesimal model and suggested that some change in variance due to change in gene frequency had occurred during the course of the experiment.
The coalescent process in models with selection, recombination and geographic subdivision
Authors: Kaplan Norman , Hudson Richard R. , Iizuka Masaru
Published: September 2009

A population genetic model with a single locus at which balancing selection acts and many linked loci at which neutral mutations can occur is analysed using the coalescent approach. The model incorporates geographic subdivision with migration, as well as mutation, recombination, and genetic drift of neutral variation. It is found that geographic subdivision can affect genetic variation even with high rates of migration, providing that selection is strong enough to maintain different allele frequencies at the selected locus. Published sequence data from the alcohol dehydrogenase locus ofDrosophila melanogasterare found to fit the proposed model slightly better than a similar model without subdivision.
Unequal crossing-over within theBduplication ofDrosophila melanogaster: a molecular analysis
Authors: Tsubota Stuart I.
Published: September 2009

TheBmutation is associated with a tandem duplication of 16A1–16A7. It is unstable, mutating to wild type and to a more extreme form at a frequency of one in 1000 to 3000. The reversion to wild type is associated with the loss of one copy of the duplication, whereas the mutation to extremeBis associated with a triplication of the region. The instability ofBhas been attributed to unequal crossing-over between the two copies of the duplication. Recent molecular data show that there is a transposable element,B104, between the two copies of the duplication and support the hypothesis that this element generated the duplicationviaa recombination event. These data suggest that unequal crossing-over within the duplication may not be the cause of the instability ofB. Instead, the instability may be caused by a recombination event involving theB104element. This issue was addressed using probes for the DNA on either side of theB104element at theBbreakpoint. All of the data indicate that theB104element is not involved in the instability ofBand support the original unequal crossing-over model.
Mitochondrial DNA heteroplasmy maintained in natural populations ofDrosophila simulansin Réunion
Authors: Matsuura Etsuko T. , Fukuda Haruyo , Chigusa Sadao I.
Published: September 2009

Mitochondrial DNA (mtDNA) variation inDrosophila simulanswas studied to determine whether the cytoplasmic state of mtDNA heteroplasmy persists in natural populations in Réunion. For this purpose, 172 isofemale lines, newly collected from two local populations, were examined, among which three types of mtDNA (siII,siIII andsiIII′) were found, based on theHpaII restriction pattern. Ten of the lines were heteroplasmic for a combination ofsiII and siIII, as determined by autoradiography. The same type of heteroplasmy had been noted in one of the two local populations 8 years before (Sattaet al.1988). The present results suggest that the heteroplasmic state occurs recurrently in natural populations ofD. simulansin Réunion.
Transposable elements in natural populations with a mixture of selected and neutral insertion sites
Authors: Charlesworth Brian
Published: September 2009

This paper examines models of the population dynamics of transposable elements when chromosomal sites vary with respect to the effect on fitness of mutations caused by element insertions. Element abundance is assumed to be stabilised solely by the joint results of transposition, excision, and selection against insertional mutations. When there are only two classes of site, selected and neutral, it is hard to find parameter values for which numbers of elements are maintained that match the findings from surveys ofDrosophilapopulations, as elements tend to accumulate at high frequencies at the neutral sites. It is similarly hard to produce realistic equilibria with three classes of site (strongly selected, weakly selected, and neutral), when elements can transpose out of the neutral sites. If transposition from neutral sites is impossible, as might be the case for elements inserted into centric heterochromatin, then realistic equilibria can be generated if there is very weak selection against elements inserted into the majority of non-neutral sites. This model predicts a modest over-representation of elements at the neutral sites. It also predicts that elements should be under-represented on the X chromosome compared with the autosomes, but this is not generally found to be the case. It is concluded that selection against insertional mutations is unlikely to be the major factor involved in the containment of element abundance.
Linkage between sperm abnormality level and major urinary protein phenotype in mice
Authors: Styrna Jozefa
Published: September 2009

Segregation of sperm abnormality level and the pattern of major urinary proteins (MUPs) were investigated in F2 and B1 hybrid males obtained from crosses involving two contrasting inbred strains of mice: CBA/Kw (Mup-1a1a, 3·3% abnormal sperm) and C57BL/Kw (Mup-1b1b, 21·9% abnormal sperm). In the progeny of both crosses mean levels of abnormal spermatozoa were significantly higher for males typed as Mup-1b1b than for heterozygous Mup-1a1b males. Moreover, all F2 hybrid males showing very high percentages of abnormal sperm were Mup-1b1bhomozygotes. Similarly, among B1 males with a high level of deformed spermatozoa, a statistically significant majority were Mup-1b1b genotypes. Our results suggest that at least two genes which influence sperm abnormality level are segregating in these crosses. Both appear to be recessive for high sperm abnormality level, and one shows weak linkage to Mup-1 on chromosome 4.
Thein vivoandin vitrotransmission ratio distortion of one complete and two partialthaplotypes in mice
Authors: Garside William , Ruangvoravat Christine , Dolan Patricia , Hillman Nina
Published: September 2009

The effects of different types of insemination (normal and delayed matings andin vitrofertilization) on the transmission ratio distortion (TRD) of threethaplotypes were determined. Thetw73haplotype which contains all of the loci known to affect TRD is transmitted at equivalent frequencies in normal matings and inin vitrofertilizations (0·84 and 0·85, respectively) but at a significantly lower frequency (0·62) in delayed matings. The distal partialth18haplotype is transmitted at equivalent frequencies in all types of insemination (0·66 to 0·70) while the proximal partialtw18haplotype is transmitted in Mendelian frequencies in normal matings and inin vitroinseminations but at a significantly lower frequency in delayed matings. The results are discussed with reference to the current genetic model for transmission ratio distortion.
An increased level of sperm abnormalities in mice with a partial deletion of the Y chromosome
Authors: Styrna Jozefa , Imai Hirotami T. , Moriwaki Kazuo
Published: September 2009

Two congenic lines of mice, one with a partial deletion of the Y chromosome, differ in the percentage of spermatozoa with abnormal heads: B10.BR/SgSn males give 22·6%; and B10.BR-Ydel/Ms males give 64·2%; abnormal sperm. The F1s resulting from crosses of B10.BR/SgSn males with females of five common inbred strains exhibited significantly lower levels of abnormal sperm than the parental strains, as opposed to F1 hybrids sired by B10.BR-Ydel/Ms mutant males, where very high levels of abnormal spermatozoa were found. About 30%; of abnormal spermatozoa, produced by males with deletion on the Y chromosome, were characterized by a flat acrosomal cap. This class of abnormality was never observed in non-mutant males, suggesting a mutant-specific defect. These results demonstrate the important role of the Y chromosome in spermatogenesis.
Genetic and molecular analysis of repression in the P–M system of hybrid dysgenesis inDrosophila melanogaster
Authors: Heath Ellen M. , Simmons Michael J.
Published: September 2009

Twelve inbred lines derived from an M′ strain ofDrosophila melanogasterwere used to study the repression of P-element-mediated hybrid dysgenesis. Initial assessments indicated that the lines differed in the ability to repress gonadal dysgenesis, and that this ability was highly correlated with the ability to represssnwhypermutability. Later assessments indicated that most of the lines with low or intermediate repression potential evolved to a state of higher repression potential; however, Southern analyses failed to reveal significant changes in the array of genomic P elements that could account for this evolution. In addition, none of the lines possessed the incomplete P element known as KP, which has been proposed to explain repression in someD. melanogasterstrains. One of the lines maintained intermediate repression potential throughout the period of study (52 generations), indicating that the intermediate condition was not intrinsically unstable. Genetic analyses demonstrated that in some of the lines, repression potential was influenced by factors that were inherited maternally through at least two generations; however, these factors were not as influential as those in a classic P cytotype strain. Additional tests with a dysgenesis-inducing X chromosome calledT-5indicated that repression itself was mediated by a combination of maternal effects and paternally inherited factors that were expressed after fertilization. These tests also suggested that in some circumstances, the P transposase, or its message, might be transmitted through the maternal cytoplasm.
Genetic and molecular analyses ofvgal: a spontaneous and unstable mutation at thevestigiallocus inDrosophila melanogaster
Authors: Bazin Claude , Lemeunier Françoise , Periquet Georges , Silber Joël
Published: September 2009

We describe herein, a new unstable mutant of thevestigiallocus, isolated from a French natural population. From this mutantvestigialalmost(vgal) wild-type flies (vgal+) and extremevgphenotypes (vge) arose spontaneously without genomic shock. The occurrence ofvgal+orvgealleles depends mostly on the breeding temperature;vgal+revertants arose principally at low temperature (21 °C) andvgeat 28 °C. These events occur mainly in the male germ line and the phenomenon appears to be premeiotic. Our results within situhybridization experiments and Southern blots show that thevgalmutation is due to a 2 kb DNA insertion, which is a deletedhoboelement. Genetic and molecular analyses show that two distinct events may underly the wild-type revertants. One is the excision of the residenthoboelement, the other a further deletion (about 300 bp in the example characterized herein). Thevgemutation is probably due to a deletion ofvestigialsequences flanking thehoboinsertion.
Muscle opacity(mo), a new mutant gene inXenopus laevis, linked to therustylocus
Authors: Droin Anne
Published: September 2009

A new developmental mutant is described inXenopus laevis(Amphibia, Anura):muscle opacity(mo). Homozygotes die at larval stage 48. The underlying defect, visible at stage 47, is a degeneration of cephalic musculature. Themogene is linked to therustylocus, with a map distance of 6·1%.
The synergistic effect of X-rays and deficiencies in DNA repair in P-M hybrid dysgenesis inDrosophila melanogaster
Authors: Margulies Lola , Griffith Carole S.
Published: September 2009

X-rays and deficiencies in DNA repair had a synergistic effect on genetic damage associated with P-element mobility inDrosophila melanogaster. These interactions, using sterility and fecundity as endpoints, were tested in dysgenic males deficient in either excision or post-replication DNA repair. Three sublines of the Harwich P strain were used for the construction of hybrid males. These sublines differ in P-induction ability based on gonadal dysgenesis sterility (GD) andsnwmutability tests, in P-element insertion site pattern, and in the types of defective P-elements, such as KP elements, they possess. A lower degree of gonadal dysgenesis was correlated with the presence of KP elements. GD sterility andsnwmutability were not always correlated. Dysgenic hybrids originating from the standard reference subline, Harwichwhite, were much more sensitive to the post-replication repair than the excision repair defect. In contrast, sterility of hybrids derived from the weak subline was least affected by, and that of hybrids of the strongest subline was most affected by either DNA repair deficiency. The exacerbation by X-rays of the effects of DNA repair deficiencies on genetic damage indicates that both repair mechanisms are required for processing DNA lesions induced by the combined effect of P activity and ionizing radiation.
Linkage of loci associated with two pigment mutations on mouse chromosome 13
Authors: Holcombe Randall F. , Stephenson Dennis A. , Zweidler Alfred , Stewart Ruby M. , Chapman Verne M. , Seidman J. G.
Published: September 2009

Progeny from one intra- and two inter-specific backcrosses between divergent strains of mice were typed to map multiple markers in relation to two pigment mutations on mouse chromosome 13, beige (bg) and pearl (pe). Both recessive mutants on a C57BL/6J background were crossed separately with laboratory strain PAC (M. domesticus) and the partially inbredM. musculusstock PWK. The intra- and inter-specific F1hybrids were backcrossed to the C57BL/6J parental strain and DNA was prepared from progeny. Restriction fragment length polymorphisms were used to follow the segregation of alleles in the backcross offspring at loci identified with molecular probes. The linkage analysis defines the association between thebgandpeloci and the loci for the T-cell receptor γ-chain gene (Tcrg), the spermatocyte specific histone gene (Hist 1), the prolactin gene (Prl), the Friend murine leukaemia virus integration site 1 (Fim-1), the murine Hanukuh Factor gene (Muhf/Ctla-3) and the dihydrofolate reductase gene (Dhfr). This data confirms results of prior chromosomal mapping studies utilizingbgas an anchor locus, and provides previously unreported information defining the localization of the prolactin gene on mouse chromosome 13. The relationship of multiple loci in relation topeis similarly defined. These results may help facilitate localization of the genes responsible for two human syndromes homologous withbgandpe, Chediak–Higashi syndrome and Hermansky–Pudlak syndrome.
Growth hormone and insulin-like growth factor-I measurements in high growth (hg) mice
Authors: Medrano J. F. , Pomp D. , Sharrow L. , Bradford G. E. , Downs T. R. , Frohman L. A.
Published: September 2009

Effects of a recessive gene causing high growth (hg) were studied on two major components of the growth axis in mice. Plasma and pituitary levels of growth hormone and plasma levels of insulin-like growth factor I (IGF-I) were measured in three lines homozygous forhg, each compared with a control line of alike genetic background but wild type for thehglocus (Hg). Line Gh (hghg) and line GH (HgHg) are from a line which had undergone long-term selection for high postweaning weight gain; line Ch (hghg) and line CH (HgHg) were extracted from the second backcross of Gh to C57BL/6J; line L54 (hghg) was from the sixth backcross to C57BL/6J (B6) (HgHg). Pituitary GH levels and plasma IGF-I levels were measured in both sexes at 3, 4·5, 6 and 9 wk of age. Plasma growth hormone was measured in 8- to 12-wk-old males at hourly intervals from 08.00 to 17.00. Body weight in lines homozygous forhgat 6 and 9 wk of age was 10–30% greater than in control lines. The ontogeny of this increased growth depended on genetic background. Pituitary growth hormone content was 52% lower in the twohghglines measured (lines Ch and Gh) than in control lines at 4·5, 6 and 9 wk. Plasma growth hormone levels were also much lower inhgmice, with values only 20–30% of those in their respective controls,hglines showed consistently low plasma growth hormone levels throughout the 9 hr sampling period, while control lines expressed the characteristic pulsatile hormone secretion. In contrast, plasma IGF-I levels were greater in line Ch (hghg) than in line CH (HgHg) at 3, 4·5 and 9 wk, and were also greater in line Gh (hghg)vs. line GH (HgHg) at 6 wk of age. The results suggest that the growth enhancing effect of thehggene occurs through an IGF-I-mediated process. In addition, the genetic background itself is also a factor in the phenotypic expression of the gene.
Genetic analysis of a switch in cell specificity of P lysozyme expression inmolossinusmice
Authors: Cortopassi Gino A. , Wilson Allan C.
Published: September 2009

An electrophoretic survey of concentrations of lysozymes M and P was carried out with seven species in the house mouse group (spretus, hortulanus, abbotti, musculus, castaneus, domesticusandmolossinus). In most species M is the predominant lysozyme in all tissues tested, except the small intestine, where P predominates if present. In inbred strains ofmolossinusmice P is more abundant than M in all tissues tested. The phenotypes of high expression of P lysozyme and low expression of M lysozyme in peritoneal and alveolar macrophages were examined genetically. Results of interspecific crosses and backcrosses todomesticusmice support the model that the phenotypes are caused by mutation(s) tightly linked to the lysozyme locus. Alleles at the regulatory loci show additive inheritance.
Two new X-autosome Robertsonian translocations in the mouse: I. Meiotic chromosome segregation in male hemizygotes and female heterozygotes
Authors: Tease Charles , Fisher Graham
Published: September 2009

Two new X-autosome Robertsonian (Rb) translocations, Rb(X.9)6H and Rb(X.12)7H, were found during the course of breeding the Rb(X.2)2Ad rearrangement at Harwell. The influence of these new Rbs on meiotic chromosome segregation was investigated in hemizygous males and heterozygous females and compared to that of Rb(X. 2)2Ad. Screening of metaphase II spermatocytes gave incidences of sex chromosome aneuploidy of 9·2% in Rb(X. 2)6H/Y and 9·6% in Rb(X.9)2Ad/Y males; no metaphase II cells were present in the testes of the Rb(X. 12)7H/Y males examined and no males with this karyotype have so far proved fertile. In breeding tests, 5% of the progeny of Rb(X.2)2Ad/Y males were sex chromosome aneuploids compared to 10% of the Rb(X. 9)6H/Y offspring. The difference was not significant, however. Cytogenetic analyses of metaphase II stage oocytes showed elevated rates of hyperhaploidy (n+ l) in Rb heterozygous females over chromosomally normal mice: 4·2% for Rb(X.2)2Ad/+; 2·1% for Rb(X.9)6H/+; 2·2% for Rb(X.12)7H/+ and 1·1% for normal females. There was, however, no statistically significant difference in the rates of hyperhaploidy between the three different Rb types, nor overall between Rb/ + and normal females. Karyotypic analyses of liveborn offspring of Rb heterozygous females revealed low incidences of X0 animals but no other type of sex chromosome aneuploidy. Intercrosses of heterozygous females and hemizygous males yielded 5·5% aneuploidy for Rb(X.2)2Ad and 5·4% for Rb(X.9)6H. In heterozygous females, there was evidence from the metaphase II and breeding test data for all three rearrangements, of preferential segregation of the Rb metacentric to the polar body resulting in a deficiency of cells and progeny carrying a translocation chromosome.
Strategies for increasing fixation probabilities of recessive mutations
Authors: Caballero A. , Keightley P. D. , Hill W. G.
Published: September 2009

Fixation probabilities and mean times to fixation of new mutant alleles in an isogenic population having an effect on a quantitative trait under truncation selection were computed using stochastic simulation. A variety of population structures and breeding systems were studied in order to find an optimal design for maximizing the fixation probability for recessive genes without impairing that for non-recessives or delaying times to fixation. Circular mating or cycles with repeated generations of close inbreeding alternating with combination of the families proved to be very inefficient. The most successful scheme found, considering fixation probabilities and times to fixation jointly, was to practise individual selection and mate full sibs whenever possible, otherwise mate at random. The benefit was directly proportional to the number of full-sib matings performed, which, in turn, almost exclusively depended on the number of selected individuals with very little effect of selection intensity or magnitude of gene effects. Fixation rates could be well approximated by diffusion methods. When selection was practised in only one sex and, therefore, the proportion of full-sib matings could be varied from zero to one, maximizing the amount of full-sib mating was found to maximize fixation probability, at least for single mutants.
A method for detecting effect of beneficial mutations in natural populations ofDrosophila melanogaster
Authors: Koga A. , Kusakabe S. , Tajima F. , Takano T. , Harada K. , Mukai T.
Published: September 2009

An experimental method is proposed for detecting the effects of positive natural selection on DNA polymorphisms. Since beneficial mutations are expected to increase in frequency faster than neutral mutations, variants which have reached high frequencies in a relatively short period could be linked to some beneficial mutation.D. melanogasterhas a cosmopolitan polymorphic inversion -In(2L)t- whose age in some local populations has been estimated. Setting the age ofIn(2L)tas the upper limit for the age of variants, we searched for variants whose frequencies were possibly influenced by positive natural selection. We detected a single candidate whose frequency and distribution met the requirements imposed by our method.
A theoretical test of the DNA repair hypothesis for the maintenance of sex in eukaryotes
Authors: Szathmáry Eörs , Kövér Szilvia
Published: September 2009

The DNA repair hypothesis for the maintenance of sex states that recombination is necessary for the repair of double-strand DNA damage. In a closed (mitotic) genetic system crossing-over generates homozygosity. This reduces fitness if deleterious recessive alleles become expressed. Thus, outcrossing is required to restore heterozygosity destroyed by recombination. The repair hypothesis is tested by comparing outcrossing sexuality with a hypothetical parthenogenic strategy (the Prudent Reparator) which destroys as little heterozygosity during repair as possible. In the Prudent Reparator, repair of double-strand DNA damage results in a small amount of homozygosity due to gene conversion only, since this process does not render outside markers homozygous. Diploidy, deleterious recessives, multiplicative fitness and linkage equilibrium in mutation-selection balance are assumed. The average fitness of this population increases, and complementation (i.e. masking of recessives in heterozygous form) decreases with the rate of damage per locus. The equilibrium fitness of the Prudent Reparator can be well above that of the sexual population. A lower complementation ability of parthenogens may not be an impenetrable barrier to their successful establishment if the invader's genome is relatively uncontaminated by mutant alleles: there are always such genotypes in the sexual population. Thus, the Prudent Reparator could solve the problem of repairing damage as well as that of invading an existing outcrossing population. As we do not see this strategy widely adopted instead of sexuality, the repair hypothesis is likely to miss some essential feature of the evolution of sex.
Inbreeding coefficients and coalescence times
Authors: Slatkin Montgomery
Published: September 2009

This paper describes the relationship between probabilities of identity by descent and the distribution of coalescence times. By using the relationship between coalescence times and identity probabilities, it is possible to extend existing results for inbreeding coefficients in regular systems of mating to find the distribution of coalescence times and the mean coalescence times. It is also possible to express Sewall Wright'sFSTas the ratio of average coalescence times of different pairs of genes. That simplifies the analysis of models of subdivided populations because the average coalescence time can be found by computing separately the time it takes for two genes to enter a single subpopulation and time it takes for two genes in the same subpopulation to coalesce. The first time depends only on the migration matrix and the second time depends only on the total number of individuals in the population. This approach is used to findFSTin the finite island model and in one- and two-dimensional stepping-stone models. It is also used to find the rate of approach ofFSTto its equilibrium value. These results are discussed in terms of different measures of genetic distance. It is proposed that, for the purposes of describing the amount of gene flow among local populations, the effective migration rate between pairs of local populations,M^, which is the migration rate that would be estimated for those two populations if they were actually in an island model, provides a simple and useful measure of genetic similarity that can be defined for either allozyme or DNA sequence data.
Nucleic acids in mummified plant seeds: biochemistry and molecular genetics of pre-Columbian maize
Authors: Rollo Franco , Venanzi Franco Maria , Amici Augusto
Published: September 2009

Nucleic acids fractions were isolated from pre-Columbian maize seeds and characterized using different approaches such as polyacrylamide gel electrophoresis, anti-DNA antibody binding, HPLC fractionation, molecular hybridization with cloned genes, and DNA amplification by the polymerase chain reaction. The nucleic acids were found to be very depolymerized (≤140 base pairs in length) and composed mainly of ribosomal RNA. Despite the very low amount and degree of polymerization of seed DNA, specific maize nuclear Mul, Mu4, Mu8 and, possibly, Mu5 element components could be detected, thanks to the use of amplification systems as short as 90 bp. The results suggest that evaluation of the relative proportions of Mu-type element components and, possibly, other maize genomic components in single mummified kernels, may offer a new key to the study of ancient maize populations.