bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of enzyme activities inDrosophila: I. The detection of regulatory loci by gene dosage responses
Authors: Rawls John M. , Lucchesi John C.
Published: September 2009

In order to detect regulatory genetic sites in the autosomes ofDrosophila melanogaster, the levels of X-linked glucose-6-phosphate dehydro-genase and autosomally linked α-glycerophosphate and isocitrate dehydrogenases have been monitored in extracts of flies aneuploid for regions of chromosomes II and III. In addition to expected structural gene dosage responses of α-GPDH and IDH, flies hyperploid for several autosome regions were found to display altered levels of one or more of the enzymes studied. While IDH activity was increased in flies hyperploid for segments of both chromosomes II and III, α-GPDH activity was decreased in specific hyperploids for chromosome II regions only. The latter group of segmental aneuploids were normal with respect to levels of chromosome II-linked alcohol dehydrogenase. To test if the observed responses were due to dosage changes of discrete genes lying within the larger effective segments, flies aneuploid for subdivisions of the chromosome segments 21A-25CD, 35A–40, and 70CD–71B were assayed. For two of these large segments so analysed, the apparent effects were attributable to specific small subdivisions, suggesting the presence of discrete regulatory sites within the latter. For the 35A–40 region the α-GPDH effect observed for subdivisions was not sufficient to account for the large α-GPDH decrease seen in flies hyperploid for the large, inclusive region. These observations are discussed with respect to the possible bases of effect of regulatory elements on enzyme activity.
Regulation of enzyme activities inDrosophila: II. Characterization of enzyme responses in aneuploid flies
Authors: Rawls John M. , Lucchesi John C.
Published: September 2009

To test whether large changes in the enzyme levels of segmentally aneuploidDrosophila melanogastercan be ascribed to changes in kinetic properties of the enzymes affected, comparisons have been made with regard to the heat stability, substrate concentration dependency, and the presence of heat-stable inhibitors or activators within the extracts of aneuploid and control flies. By these criteria, no differences were found between controls and the α-GPDH activity of flies trisomic for chromosome II segments 27D–31E, 35A–40, 41–45F, and 57B–60F and no differences were evident between the IDH properties of 70CD–71B aneuploids and their controls. The enzyme changes observed in these aneuploids are more likely associated with changes in the rates of accumulation of the enzyme molecules. The IDH of flies trisomic for the 27D–31E region was more heat-stable than that of controls while the α-GPDH of flies trisomic for the 21A–25CD region displayed an apparent Michaelis constant for α-glycerophosphate lower than that of controls. The possible bases for these latter qualitative distinctions are discussed.
Mitotic crossing-over in a higher plant
Authors: Carlson Peter S.
Published: September 2009

This paper provides direct evidence for the occurrence of mitotic crossing-over in leaf tissues andin vitrocell cultures ofNicotiana tabacum. The geno-typic composition of both segregating regions of twin spots was analysed byin vitroculture of the segregating tissue and by regenerating plants from this tissue. The frequency of mitotic crossing-over is influenced by several physical and chemical agents.
A note on increasing the limit of selection through selection within families
Authors: Dempfle Leo
Published: September 2009

It is shown that, in a finite population, by ensuring an equal contribution of offspring from each family we achieve a higher selection limit than by using mass selection, given that the correlation between selection criterion and additive genetic value is sufficiently high. The difference between the selection limits of the two schemes increases with more intense selection. The theoretical results were verified by Monte Carlo Simulation, and the influences of several factors were investigated. It is shown that such a breeding scheme might be useful in dairy cattle.
Fitness of allozyme variants inDrosophila pseudoobscura: II. Selection at theEst-5, OdhandMdh-2loci
Authors: Marinković Dragoslav , Ayala Francisco J.
Published: September 2009

We have studied the effects on fitness of allelic variation at three gene loci (Est-5, Odh, andMdh-2)coding for enzymes inDrosophila pseudoobscura. Genotype has a significant effect on fitness for all six parameters measured (female fecundity, male mating capacity, egg-to-adult survival under near-optimal and under competitive conditions, and rate of development under near-optimal and under competitive conditions). No single genotype is best for all six fitness parameters; rather, genotypes with superior performance during a certain stage of the life-cycle may have low fitness at some other stage, or in different environmental conditions. Heterozygotes are sometimes best when all fitness parameters are considered. There are significant interactions between loci. The various forms of balancing selection uncovered in our experiments may account for the polymorphisms occurring in natural populations ofD. pseudoobscuraat the three loci studied.
The effect of population subdivision on two loci without selection
Authors: Feldman Marcus W. , Christiansen Freddy Bugge
Published: September 2009

This paper is devoted to the study of the effects of population subdivision on the evolution of two linked loci. Two simple deterministic models of population subdivision without selection are investigated. One is a finite linear ‘stepping stone’ model and the other is a finite linear stepping stone chain of populations stretching between two large populations of constant genetic constitution. At equilibrium in the first model the gene frequencies in each population are equal and there is linkage equilibrium in each population. The rate of decay to zero of the linkage disequilibrium functions is the larger of (1 –c) and, where λ1is the rate of convergence of the gene frequencies to equilibrium and c is the recombination frequency. In the second model at equilibrium there will be a linear cline in gene frequencies connecting the two large constant populations. This cline will be accompanied by a ‘cline’ of linkage disequilibria. The rate of convergence to this equilibrium cline is independent of the recombination frequency, and, in fact, the gene frequencies and the linkage disequilibria converge to equilibrium at the same rate.
Uncorrelated genetic drift of gene frequencies and linkage disequilibrium in some models of linked overdominant polymorphisms
Authors: Felsenstein Joseph
Published: September 2009

For large population sizes, gene frequenciespandqat two linked over-dominant loci and the linkage disequilibrium parameterDwill remain close to their equilibrium values. We can treat selection and recombination as approximately linear forces onp, qandD, and we can treat genetic drift as a multivariate normal perturbation with constant variance-covariance matrix. For the additive-multiplicative family of two-locus models,p, qandDare shown to be (approximately) uncorrelated. Expressions for their variances are obtained. When selection coefficients are small the variances ofpandqare those previously given by Robertson for a single locus. For small recombination fractions the variance ofDis that obtained for neutral loci by Ohta & Kimura. For larger recombination fractions the result differs from theirs, so that for unlinked loci r2≃ 2/(3N) instead of 1/(2N). For the Lewontin-Kojima and Bodmer symmetric viability models, and for a model symmetric at only one of the loci, a more exact argument is possible. In the asymptotic conditional distribution in these cases, various ofp, qandDare uncorrelated, depending on the type of symmetiy in the model.
Selection for growth-rate during asexual and sexual propagation in Phytophthora cactorum
Authors: MacIntyre Donald , Elliott Charles G.
Published: September 2009

Selection for high and low growth-rate was carried out during eight generations of asexual propagation by zoospores and seven generations of sexual reproduction by oospores. The fungus has previously been shown to be diploid during its vegetative phase. In the zoospore lines there was no significant variation and no response to selection, except for the occasional appearance of fast-growing sectors. A high line was established from such a sector; in its sexual progeny the inheritance of growth-rate was non-Mendelian. Propagation through self-fertilized oospores released very considerable genetic variation, and both high and low lines responded to selection. At first the variation within families, and the response to selection, increased with succeeding generations, despite the intense inbreeding. In later generations the high line became less variable, and the progeny oospore cultures resembled the fast-growing sectors. It is concluded that growth-rate is controlled by a polygenic system and by cytoplasmic determinants, a mutant form of which is responsible for the fast-sectoring phenotype.
The lactose system inKlebsiella aerogenesV9A: 4. A comparison of thelacoperons ofKlebsiellaandEscherichia coli
Authors: Reeve E. C. R. , Braithwaite J. A.
Published: September 2009

Klebsiella aerogenesV9A contains twolacoperons, one chromosomal and one borne by the Lac plasmid,FKlac. It is shown that the plasmid Lac repressor resembles that ofEsherichia coliin that it represses theE. colioperon but is inactivated by melibiose. In contrast, the chromosomal Lac repressor of V9A is unable to repress theE. colioperon or the FKlacoperon, but is converted into an active repressor of both these operons on becoming bound to melibiose. The chromosomal Lac repressor is able to repress its own operon whether or not it is bound to melibiose, but is inactivated by isopropyl-β-D-thiogalactoside. These results support the hypothesis that theKlebsiellaLac plasmid was derived from an ancestralE. colichromosome.
Six new loci controlling resistance top-fluorophenylalanine inAspergillus nidulans
Authors: Srivastava Sheela , Sinha Umakant
Published: September 2009

Twelve FPA-resistant mutants were selected on medium containingp-fluorophenylalanine and ethionine. Dominance tests in heterozygous diploids showed that 8 out of 12 are dominant and 4 recessive to their wild-type alleles. One mutant,fpa60, showed a partial requirement for tyrosine and was found to be allelic to anfpaAmutant described previously. A tyrosine non-requirer,fpa65, was also assigned to this locus. The other 10 mutants did not show any growth requirement and were simultaneously resistant to ethionine and 3-amino-L-tyrosine. Of the 8 dominant mutants, 3 were allelic to the permease-mutants at the locusfpaD.Dominant mutants showed higher degrees of resistance than recessive ones. Six new loci, identified after preliminary genetic analysis, were located on 3 linkage groups: 3 on linkage group VI, and one each on linkage groups I, V, and VIII. The recombinantfpaD11;fpaK69 was found to be sensitive to FPA.
Nuclear and cytoplasmic cross-resistance and correlated sensitivity to DNA intercalating drugs in a petite-negative yeast
Authors: Celis Esteban , Mas Jaime , Brunner Aurora
Published: September 2009

Ethidium bromide and acriflavin-resistant mutants of petite-negative yeastKluyveromyces lactiswere prepared. One kind of nuclear mutation (EBR1) gave resistance to ethidium bromide and correlated sensitivity towards acriflavin. Another nuclear mutation (EBR2) did not affect ‘natural’ resistance of this yeast towards 15 μM acriflavin. Both nuclear mutations mapped at differentloci, suggesting lack of linkage. Cytoplasmic mutants resistant to these two drugs were unstable when grown in complete media with dextrose, reverting to a wild-type resistance genotype. When grown in glycerol-containing media these mutants maintained their cytoplasmic drug-resistance conferring factors.
On sojourn times at particular gene frequencies
Authors: Pollak Edward , Arnold Barry C.
Published: September 2009

The distribution of visits to a particular gene frequency in a finite population of sizeNwith non-overlapping generations is derived. It is shown, by using well-known results from the theory of finite Markov chains, that all such distributions are geometric, with parameters dependent only on the set ofbij's, wherebijis the mean number of visits to frequencyj/2N, given initial frequencyi/2N. The variance of such a distribution does not agree with the value suggested by the diffusion method. An improved approximation is derived.
Chromosomal location of prophage J51 inPseudomonas aeruginosastrain PAO
Authors: Carey K. E. , Krishnapillai V.
Published: September 2009

The UV-inducible prophage J51 has been mapped late on the chromosome ofP. aeruginosastrain PAO, relative to the entry point of the sex factor FP2. This was determined following the analysis of the segregation of unselected markers in conjugational crosses between appropriately marked donor and recipient strains. A more precise location of about 50 min was obtained from the kinetics of increase in infectious centres due to zygotic induction during interrupted mating experiments.
Evidence that Linkage Group IV as well as Linkage Group X of the mouse are in chromosome 10
Authors: Cacheiro N. L. A. , Russell Liane B.
Published: September 2009

Four translocations in which one breakpoint was known to be at or closely linked to the LGIV marker Steel, Sl, were studied in an attempt to identify cytologically the as yet unassigned Linkage Group IV of the mouse. The cytological results indicate that chromosome 10, which had previously been matched with LGX, is involved in each of the four translocations, the break being in 10D. Recombination between Sl and the LGX marker grizzled, gr, was determined to be 6–14%. The combined cytological and genetic results indicate that LGIV and LGX are both in chromosome 10, and that the order may be centromere-gr-Sl.
An experiment on recombination load inDrosophila melanogaster
Authors: Charlesworth Brian , Charlesworth Deborah
Published: September 2009

This paper describes the results of an experiment to measure the effect on mean population fitness of recombination in the second chromosome ofDrosophila melanogaster. There was a small and non-significant effect of recombination in lowering egg-to-adult viability of heterozygotes for wild-type chromosomes. A large (7%) and significant effect of recombinant chromosomes on the fecundity ofCyfemale carriers was detected.
Properties of the R factor R144drd3 inKlebsiella pneumoniaestrain M5a1
Authors: Dixon R. , Cannon F. C. , Postgate J. R.
Published: September 2009

The R factor, R144drd3, mobilized chromosomal genes inKlebsiella pneumoniaestrain M5a1 at similar frequencies to those observed for this R factor inEscherichia coliK12. In a derivativeK. pneumoniaedonor, strain HF3, R144 persisted in the autonomous state but now gave rise to polarized transfer of the chromosome in the order Ohis…arg2…leu…trp. R144drd3 was unstable inK. pneumoniaeM5a1; after successive subculture drug resistance, colicinogeny and transmissibility were lost. In strain HF3, transmissibility was preferentially lost, but determinants for drug resistance, colicinogeny and superinfection immunity were retained; 10–11 copies per chromosome of R144 were present in log phase cultures of both strains.
Probability of identical monomorphism in related species
Authors: Nei Masatoshi , Li Wen-Hsiung
Published: September 2009

A mathematical method for evaluating the probability that a locus is monomorphic for the same allele in related species is developed under the neutral mutation hypothesis. A formula for the proportion of identically monomorphic loci in related species is also worked out. The results of the application of this method toDrosophiladata do not support Prakash & Lewontin's (1968) contention that the strong association between gene arrangements (inversion chromosomes) and alleles at protein loci is evidence of coadaptation of genes in the inverted segment of chromosomes. Similarly, unlike Haigh & Maynard Smith's (1972) contention, the monomorphism of the haemoglobin α chain locus in man can be accommodated with the neutral mutation hypothesis without invoking the bottleneck effect.
Alcohol dehydrogenase activity inDrosophila melanogaster: a quantitative character
Authors: Ward R. D.
Published: September 2009

Alcohol dehydrogenase activity inDrosophila melanogastermay be considered as a quantitative character, since it shows many features typically associated with such traits. Although strains with the electrophoretically fast phenotype generally have activities greater than those with the slow phenotype, presumably reflecting differences in the nucleotide sequences of the structural alleles, within each electrophoretic class there is considerable variation in activity. The expression of the structural gene, in terms of ADH activity, is to some extent regulated by its genetic background. Strains homozygous for particular structural alleles respond to divergent directional selection for ADH activity. Modifiers have been located to theX, second and third chromosomes.
Observations on a set of radiation-induced dominantT-like mutations in the mouse
Authors: Bennett Dorothea , Dunn L. C. , Spiegelman Martha , Artzt Karen , Cookingham Janice , Schermerhorn Elizabeth
Published: September 2009

Genetic analysis of seven dominant short tailed mutations independently induced by radiation of male mice showed that six were allelic toT(Brachyury) but not identical to it. Homozygotes for each mutant die at least 2 days earlier thanT/Thomozygotes; two that were studied histologically are indistinguishable from one another. The development of these abnormal embryos is arrested by seven days of gestation, when cells of embryonic ectoderm cease proliferation and become pycnotic. Endoderm and extra-embryonic ectoderm do not seem to be primarily affected, and survive and grow for at least 2 days more. Serological studies of one of these mutations suggest that it is a deletion. A review is presented of these and otherT-like mutations that have been described; from this it appears that five different categories ofT-like mutants are discernible.
Efficient curing of anEscherichia coliF-prime plasmid by phenothiazines
Authors: Mándi Y. , Molnár J. , Holland I. B. , Béládi I.
Published: September 2009

Chlorpromazine and several other phenothiazines at sub-bacteriocidal concentrations were found to cure anEscherichia coliF′lac+strain of its plasmid efficiently. Curing was most efficient at high pH and in complex medium when 70% or more of the bacteria were plasmid-free after 24 h growth of cultures in the presence of the drug.
The effects of temperature on aberrant ascus frequencies at theBufflocus inSordaria brevicollis
Authors: Ahmad A. F.
Published: September 2009

Single-point crosses using five allelic spore colour mutants at thebufflocus were carried out at different temperatures. The data suggest (i) that fixed or preferred opening points in the DNA, required for initiation of recombination events, are available more often at higher than at lower temperatures, (ii) opening points at or beyond both proximal and distal ends of thebufflocus respond similarly to variations in temperature, and (iii) the correction pattern seems to be independent of temperature at thebufflocus inS. brevicollis.
Biochemical characterization and genetic mapping of purine genes inMicrococcus luteus
Authors: Mohapatra Nirupama , Kloos Wesley E.
Published: September 2009

Purine auxotrophs ofMicrococcus luteuswere induced byN-methyl-N′-nitro-N-nitrosoguanidine. They were biochemically characterized by growth stimulation with CO2-enriched air and purine intermediates and by the Bratton-Marshall test that is used to detect accumulated diazotizable amines. The mutants were divided into four classes:pur(EC),purH,purJ, andPur−. Thepur(EC) class was further subdivided intopurEandpurCby results of crossing all thepur(EC) mutants with a knownpurEreference strain (ATCC 27141). Mutants which were not linked to the referencepurEmarker were considered to bepurC. Genetic mapping was accomplished by using two-point reciprocal transformation crosses. The result of this study indicates thatpurJmutants may be loosely linked topurEandpurC, and purH mutants are not linked topurE,purCorpurJ.
Crossing over between closely linked markers spanning the centromere of chromosome 3 inDrosophila melanogaster
Authors: Sinclair Donald A.
Published: September 2009

Recombination in a short genetic interval spanning the proximal region of chromosome 3 was studied in the regionsst-in-ri-eg2-Ki-pp. Crossover frequencies in this region varied considerably in different genetic backgrounds; however, in all genotypes, the following observations were made: (1) an excess of multiple recombinant chromosomes indicative of high negative interference, was detected; (2) among the multiple recombi-nants, a positive correlation of simultaneous exchange in the most proximal and shortest adjacent genetic intervals was noted; (3) several classes of reciprocal products were not equally recovered. Three possible explanations for these results are: pre-meiotic exchange, chromatid interference and gene conversion.
The genetic locations oftraO, finPandtra-4 on theE. coliK12 sex factor F
Authors: Willetts Neil , Maule John , McIntire Sarah
Published: September 2009

Using a series of Hfr and F prime deletion strains, the F transfer inhibition genefinPhas been mapped betweenoriandtraJ. Marker rescue experiments with the Hfr deletion strains further showed thattraO, the site of action of the transfer inhibitor, is located immediately to the left of, or possibly within,traJ, and that the polar mutationtra-4lies intraK.
Mapping the adrenal lipid depletion gene of the AKR/J mouse strain
Authors: Taylor B. A. , Meier H.
Published: September 2009

The pattern of inheritance of the autosomal recessive adrenal lipid depletion (ald) allele among the AKXL recombinant inbred mouse lines, derived from a cross between AKR/J and C57L/J, revealed that thealdlocus is located on chromosome 1 near the dipeptidase-1 (Dip-1) locus. The linkage was confirmed in a backcross generation and the gene orderln-Dip-1-aldwas established.
Relative retention of mitochondrial markers in petite mutants: mitochondrially determined differences betweenRHO(+) strains
Authors: Molloy P. L. , Linnane Anthony W. , Lukins H. B.
Published: September 2009

The relative frequency of retention of two mitochondrial loci, determining resistance to oligomycin (oli1) and erythromycin (ery1), has been analysed in petite (rho(−)) mutants derived from a number of unrelated strains ofSaccharomyces cerevisiae. The frequency of retention of one marker relative to the other in spontaneous petites showed marked variation dependent on the strain of origin. The differences between strains in this characteristic were shown to be mitochondrially determined. Further, for individual strains, the relative retention of the markers in petites derived after UV-irradiation varied considerably in several cases from that observed with spontaneous petites. The observations on relative marker retention and the varied effects of UV-irradiation are discussed in terms of possible structural differences in the mitochondrial genomes of the various strains.
Mapping an invisible lethal in the mouse
Authors: Wallace Margaret E.
Published: September 2009

An effective breeding policy is described for detecting linkage in the mouse, for an ante-natal lethal from crosses of heterozygotes with stocks homozygous for several linked recessive markers. A method of analysing the ensuing data is described, together with a method of estimating the map distance to close markers. A practical illustration is described, involving an ante-natal lethal obtained from a colony of wild mice and a four fold recessive chromosome 2 marker stock.
Ovulation rate of lines of mice selected for testis weight
Authors: Mafizul Islam A. B. M. , Hill W. G. , Land R. B.
Published: September 2009

Selection was practised in two replicates for both high and low testis weight in the mouse. Typically 7 males were selected out of 30 recorded for a total of 5 generations. From an initial average of 191 mg the mean divergence between high and low lines reached 112 mg, with a realized heritability of 0·52. The ovulation rate of the lines changed in the same direction as that of selection, the mean divergence was 2·0 eggs in primiparous females in generation 4 and 1·6 in nulliparous females in generation 5. Correlated changes in the body weight of both sexes also occurred but were inadequate to account for the observed change in ovulation rate. The genetic regressions of ovulation rate on testis weight were estimated to be 2·9 and 14 eggs/100 mg in primiparous and nulliparous females, respectively, which, along with data from other experiments, correspond to genetic correlations between testis weight and ovulation rate of 0·50 and 0·25 respectively. There were no correlated changes in litter size. The possibility of using male testis size in breeding programmes to improve female reproductive performance is discussed.
Genetics of plate morphology in an unusual population of threespine sticklebacks (Gasterosteus aculeatus)
Authors: Avise John C.
Published: September 2009

A collection ofGasterosteus aculeatusfrom a single locality (Friant) in Madera County, California, contains individuals with low and high lateral plate morphology, and very few intermediates. Electrophoretic evidence on protein similarities at 15 genetic loci is compatible with the thesis that members of these two morphs belong to a single interbreeding population. This thesis is also supported by broods from laboratory crosses between morphs, which segregate for low and high plate counts. Laboratory crosses between Friant fish and those from geographically isolated populations often yield some progeny with intermediate plate counts. The demonstration of significantly different patterns of plate development in intralocality versus interlocality crosses evidences a contrasting genetic basis for plate determination in different populations of sticklebacks.
The incidence of chromosomally unbalanced gametes in T(14; 15)6 Ca heterozygote mice
Authors: Kaufman M. H.
Published: September 2009

When T6/+ female mice were mated to non-translocation-bearing males, the relative viability of the embryos at 13·5–14·5 days gestation was about 39%. About 36% of the oocytes ovulated by T6/+ females were aneuploid, as a result of non-disjunction at meiosis, the majority having either 19 or 21 chromosomes. However, aneuploidy only accounts for a proportion of the embryonic loss in T6/+ × +/+ matings, as many of the embryos with 41 chromosomes survive postnatally. The present findings indicate that approximately 50% of the oocytes ovulated with the normal haploid number of chromosomes (n= 20) were genetically unbalanced as a result of adjacent segregation, and that a high proportion of the resultant embryos die in the early postimplantation period. In the present study non-translocation-bearing mice which were genotypically similar to the T6/+ females acted as controls.
The hitch-hiking effect – a reply
Authors: Haigh John , Smith John Maynard
Published: September 2009

We have no serious disagreement with the mathematical arguments presented by Ohta & Kimura (1975). We do, however, have reservations about their conclusions that ‘the hitch-hiking effect is generally unimportant as a mechanism for reducing heterozygosity’, and still prefer our own approach (Maynard Smith & Haigh, 1974).
Selection and analysis of a mutantParamecium tetraurelialacking behavioural response to tetraethylammonium
Authors: Chang Sheng-Yung , Kung Ching
Published: September 2009

We selected a mutantParamecium tetraureliawhich does not exhibit avoiding reaction in solutions of tetraethylammonium (TEA+), a known membrane K+-channel blocker. Behavioural reaction of the mutant to Na+solutions was also weak. The rapid successions of avoiding reactions in Ba2+solutions were observed in both wild type and the TEA-insensitive mutant. Formal genetic analyses showed that this mutant is due to a recessive mutation. This mutation is on a gene completely unlinked to and hypostatic in different degrees to the genes for the membrane defects of ‘pawn A’, ‘pawn B’, ‘ts-pawn C’, ‘fast-2’ and ‘paranoiac A’.
Covalently closed, circular DNA in kappa endosymbionts ofParamecium
Authors: Dilts Judith A.
Published: September 2009

Caedobacter taeniospiralis(kappa), a bacterial endosymbiont isolated fromParamecium tetraureliastock 51, contains, in addition to the bacterial chromosome, covalently closed circular DNA molecules as shown by isolation on dye-buoyant-density gradients. The closed circular molecule has a contour length of 13·75 ± 0·04 µm with a buoyant density of 1·698 g/cm3. The buoyant density of the bacterial chromosome is 1·700–1·701 g/cm3. Kappa of the 51 group isolated from stock 298 and stock 6g2,P. tetraurelia, also contain the closed circular DNA. Two forms of kappa coexist in paramecia: brights and nonbrights. Examination by density-gradient centrifugation of the DNA of brights and nonbrights shows the extrachromosomal DNA to be associated mainly with brights. It is suggested that the extrachromosomal DNA might be the determinant for the refractile bodies and the helical phage-like structures found in brights.
Synchrony of division in mass cultures of Paramecium tetraurelia by a selective density-labelling technique
Authors: Aufderheide Karl
Published: September 2009

A technique has been developed for achieving synchrony of division by selection for immediate pre- and post-fission cells of Paramecium tetraurelia. Cell populations are fed granular tantalum, followed by density-gradient centrifugation. Dividing cells, which do not feed, are separated from feeding interphase cells. The selected cells are division-synchronous for at least two generations when resuspended in fresh culture fluid. This technique provides a rapid means of obtaining large numbers of synchronously dividing paramecia for cell-cycle studies and has general application for selective enrichment of non-feeding sub-populations of cells.
A study on the mate-killer toxin by microinjection inParamecium
Authors: Koizumi Sadaaki , Kobayashi Sumiko
Published: September 2009

The killing action by mu toxin, which is contained in the cytoplasm of stock 540,Paramecium primaurelia, was demonstrated against the various stocks of paramecia by means of microinjection. Most of the toxin is present in the soluble fraction of the host cytoplasm. The toxin was precipitated by ammonium sulphate at 50–80% saturation, and was almost completely inactivated by incubation at 60 °C for 30 min. Pre-autogamous paramecia were more sensitive than post-autogamous ones to the toxin. Paramecia which bear endosymbionts were generally resistant to the mate-killer toxin.
Longitudinal microtubules and their functions during asexual reproduction inParamecium tetraurelia
Authors: Sundararaman V. , Hanson Earl D.
Published: September 2009

Longitudinal microtubules appear inParamecium tetraureliawhen cells are ready to divide (ca.interfission age 0·9). They arise in the longitudinal cortical ridges between kineties and form, in each ridge, an incomplete circlet of 15–18 microtubules, disappearing 10–15 min after separation of the fission products (ca.interfission age 0·03–0·04). Vinblastine, colchicine, colcemid, mercaptoethanol, and cold treatments all result in loss of these microtubules, rounding up of the cells, and some suppression of cell division. The tubules are thought to play a role in cellular elongation, morphogenesis, and separation.
Laser microbeam induction of incomplete doublets of Oxytricha fallax
Authors: Grimes Gary W.
Published: September 2009

Destruction by laser microbeam of oral and ventral cirral primordia for the future opisthe of 1/2 of a pre-fission doublet results in the permanent loss of ability to form oral and ventral cirral primordia on the irradiated half. This observation provides further evidence for the postulated ‘determinative region’ present on each ventral surface of these organisms. The opisthe of the irradiated doublet retains both original rows of marginal cirri, which are located mid-dorsally with respect to the remaining ventral surface. These two rows of marginal cirri are reproduced faithfully in all future opisthes, but are lost in most proter lines. The pattern of loss in proters involves migration of the extra rows of marginal cirri to the cell's right margin followed by aberrant morphogenesis and subsequent resorption. These results show that the reproduction of marginal cirri is at least partially dependent upon the presence of marginal cirri and their inherent structural characteristics as well as upon their position on the cell surface.
Maintenance of genetic homogeneity in systems with multiple genomes
Authors: Birky C. William , Skavaril Russell V.
Published: September 2009

Genes or sequences of DNA present in multiple copies per cell include entire genomes of mitochondria and chloroplasts, nuclear ribosomal RNA genes, and highly repetitive sequences in heterochromatin. All copies are nearly identical, in spite of mutational pressure and weak selection. A zygote containing mitochondrial or chloroplast genophores of two different genotypes quickly produces progeny pure for one genotype or another (vegetative segregation). Evidence from yeast andChlamy-domonassuggests that organelle genophores undergo repeated rounds of random mating and recombination. When two molecules carrying different alleles at a locus recombine, gene conversion can result in the cell becoming pure for one allele. Stochastic matching and conversion (SMAC) has been studied by computer simulations which suggest that it will tend to eliminate new mutations in yeast mitochondrial DNA and speed up vegetative segregation. We have verified previous suggestions that gene conversion, occurring during unequal mitotic sister-strand crossing-over, provides an efficient mechanism for maintaining the homogeneity of repeated sequences in eukaryotic chromosomes.
Effects of actinomycin D and puromycin upon excystment ofDidinium nasutum
Authors: Butzel H. M. , Mayer L.
Published: September 2009

Activated cysts ofDidinium nasutumcontinue excystment after treatment with actinomycin D or puromycin. Cysts treated at developmental stages 19–20 emerge holociliated and lacking the seizing organ. No effect of the antibiotics at any other stages was found, suggesting that it is at stage 19–20 that the initiation of normal ciliation and of mouth formation occurs. Treatment with other metabolic inhibitors either blocks excystment completely or has no effect on normal development depending upon dosage, suggesting that the action of the antibiotics is specific.
Evidence that HT mutant strains of bacteriophage P22 retain an altered form of substrate specificity in the formation of transducing particles inSalmonella typhimurium
Authors: Chelala Cesar A. , Margolin Paul
Published: September 2009

The effects of two different deletions of the tryptophan operon on the cotransduction linkage of the nearbycysBandpyrFmarkers were studied using three sets of donor lysates, each produced by a different HT mutant P22 phage strain. Eachtrpoperon deletion (present in both donor and recipient to preserve homology) caused changes in the cotransduction frequencies. This indicated that the HT mutant phage encapsulating mechanism, whose ability to discriminate phage DNA from host-cell DNA is absent or diminished, could still distinguish among nucleotide sequences in selecting bacterial chromosome sites at which to initiate transducing particle formation. The three HT mutant phage strains each produced different sets of cotransduction linkage values, indicating that this aspect of substrate specificity was altered differently and uniquely by each HT mutation.
The association of tryptophan synthetase subunits fromEscherichia coliandSalmonella typhimuriumin homologous and heterologous combinations
Authors: DiCamelli Ralph Francis , Balbinder Elias
Published: September 2009

The association of α and β2subunits of tryptophan synthetase fromEscherichia coliandSalmonella typhimuriumin homologous and heterologous combinations was studied by sucrose density gradient centri-fugation. Under conditions allowing for optimal association of subunits derived from the same source, subunit association in the mixtureE. coliα–S. typhimuriumβ2was weaker than normal while in the reciprocal combination ofS. typhimuriumα–E. coliβ2it was tighter than normal.

These observations suggest that a certain degree of binding between the α and β2subunits of tryptophan synthetase could have had a selective advantage during the evolutionary divergence of the species of Entero-bacteriaceae, so that a mutation leading to the substitution of an amino acid involved in α–β2association in one of the subunits could have been compensated by a mutation in the complementary one.
Lysogenization by phage P22 carrying amber mutations in Genes 12 and 18
Authors: Ronen Amiram , Levine Myron
Published: September 2009

Temperature-sensitive mutants in genes 12 and 18 of phage P22 show recessive DNA-negative phenotypes, but dominant integration-negative phenotypes. In contrast, am mutants in genes 12 and 18 are recessive for both DNA synthesis and lysogeny. The data are interpreted to indicate that the active forms of these two gene products are multimers.
Quantitation of nuclear DNA inAscaris lumbricoides: DNA constancy and chromatin diminution
Authors: Pasternak J. , Barrell R.
Published: September 2009

The DNA contents of nuclei during gametogenesis and embryogenesis inAscaris lumbricoideswere measured by Feulgen-microspectrophoto-metry. The variability in the mean value for the haploid amount of DNA in sperm from different males processed at different times was not significant when sperm cell samples were taken from the same region of the seminal vesicle. As the sperm mature, the extent of uptake of Feulgen dye decreases nonsystematically. A similar phenomenon occurs during embryogenesis, and as noted by others, primary oocytes in the terminal portion of the oviduct become Feulgen-negative. Feulgen-positive primary oocytes maintain a 4C DNA value without significant variation. Notwithstanding the differences in Feulgen-DNA values in certain types of nuclei, our evidence supports the view that inAscaris lumbricoidesthe amount of intraspecific DNA has a constant value between individual organisms and from one generation to the next. About 34% of the DNA of the zygote is lost through chromatin diminution at the third embryonic cleavage. This quantity represents 0·23 pg DNA per haploid equivalent.
Plasmid-mediated transmission of chromosomal genes inPseudomonas glycinea
Authors: Lacy George H. , Leary John V.
Published: September 2009

Complementing diauxotrophic mutants ofP. glycineawere mated in combination in which one or both mutants contained a resistance plasmid. The transfer of chromosmal markers was scored by the appearance of prototrophy at one or more of the auxotrophic loci. The resistance plasmid RP1 was equally or slightly more efficient than R6886 in the transmission of chromosomal genes.
The effects of selection at different ages for high and low body weight on the pattern of fat deposition in mice
Authors: Hayes J. F. , McCarthy J. C.
Published: September 2009

Two pairs of lines of mice, selected for High and Low weight at 5 weeks of age (H5and L5) and at 10 weeks of age (H10and L10) over 15 generations, were compared with each other and an unselected control line (QC) at three different ages, i.e. at 5, 10 and 21 weeks of age. Differences in percentage fat between High and Low lines were small at 5 weeks, clearcut at 10 weeks and at 21 weeks the High lines were almost twice as fat as the Low ones. The H5line was slightly fatter than the H10line at all three ages and the L10line was fatter than the L5line at two ages. The developmental pattern of fat deposition was unaffected by selection for high or low weight at 5 weeks, i.e. the relationship between fat weight and carcass weight was similar in the H5, L5and QC lines. Selection at 10 weeks affected the level of fat at low carcass weights and the relative rate at which fat was subsequently deposited. The different correlated responses resulting from selection at 5 and 10 weeks are explained in terms of genetic variation in (1) the rate of food consumption, (2) the efficiency of energy utilization for growth, and (3) the relative amount of fat deposited up to the age at selection.
The effect of selection for body weight on the skeletal variation of the mouse
Authors: Truslove Gillian M.
Published: September 2009

The incidence of many minor skeletal variants in the inbred mouse strain C57BL can be influenced by the diet on which the parents live: in many cases, the effect is mediated by a correlation with body size. This also seems to be true in Falconer's (1973) Q-strain in which body size has been increased or decreased by selection. However, there was so much heterogeneity between replicates within selection lines that variants influenced by body size could be detected as a group, but not identified individually.
The survival of RP 1–1 inEscherichia coliand the influence of therecandpolAgenes on the process
Authors: Moillo-Batt Agnes , Richmond M. H.
Published: September 2009

The survival of the plasmid RP 1–1 inE. colidepends on the presence of a functionalpolAgene. Unlike other plasmids that have this requirement, the replication of RP 1–1 is inhibited by chloramphenicol. RP 1–1 cannot be inherited byE. coli recAmutants, and inactivation of therecAgene product in arecAtsmutant leads to destruction of the plasmid. RP 1–1 cannot be inherited byrecBorrecC E. coliunless the strains also carry a suppressor of these genes, such assbcAorsbcB. The pattern of replication of RP 1–1 inE. coliK12 and its mutants suggests that the survival of this plasmid in this species is the outcome of a balance between DNA polymerase I-specified replication and exonuclease destruction.
A selective model for electrophoretic profiles in protein polymorphisms
Authors: Moran P. A. P.
Published: September 2009

In a previous paper the theory of a model of electrophoretic profiles due to Ohta & Kimura was considered. This model assumes a finite population with a linear series of possible alleles with mutation between nearest types but no selection. In the present paper a model with both mutation and selection is constructed which results in a stable population distribution closely fitting empirically observed features of the Ohta–Kimura model. The problem of discriminating between selective and non-selective models for electrophoretic models is considered.
Behavioural pleiotropy of theyellowgene inDrosophila melanogaster
Authors: Wilson R. , Burnet B. , Eastwood L. , Connolly K.
Published: September 2009

Theyellowmutant (y− 1:0·0) ofDrosophila melanogastershows a reduction in body pigmentation associated with a decrement in locomotor activity and in male competitive mating ability. The effects of the mutant gene are specific to locomotor activity in the adult fly, measures of larval activity being unaffected. In the presence of active femalesyellowmales offer a reduced intensity of sexual stimulation because they are less able to maintain contact during courtship. However, the impaired locomotor performance ofyellowmales is not the general cause for their reduced competitive mating ability, since the stimuli provided byyellowmutants courting inactive females appear to be both quantitatively and qualitatively indistinguishable from those of their wild-type male sibs. Nor is there any good evidence, as measured by the frequency of rejection responses, that the courtship stimulation offered by theyellowmales is less acceptable to the females. The mutant males are nevertheless unsuccessful in achieving copulation with such females. It is suggested that impairment of mating ability inyellowmales may be caused by changes in the efficiency for mating of their secondary sexual structures due to the effect of theyellowgene on the properties of the cuticle.
Tetrapyrrole biosynthesis:N-methyl-N′-nitrosoguanidine-induced mutants ofPropionibacterium shermanii
Authors: Georgopapadakou N. H. , Petrillo J. , Scott A. I. , Low B.
Published: September 2009

An isolation method forN-methyl-N′-nitrosoguanidine-induced catalase negative mutants ofP. shermaniibased on replica plating is described. In contrast to previous methods, it extends to the early stages of tetrapyrrole biosynthesis which are common in both corrins and porphyrins. It may thus aid in elucidating the mechanism and control of porphyrin and corrin biosynthesis. Some preliminary results are discussed.
Strain variation in spermatozoal β-glucuronidase in mice
Authors: Erickson Robert P.
Published: September 2009

Variation in spermatozoal β-glucuronidase levels of inbred strains of mice was found to parallel the known variation usually studied in liver with one outstanding exception: BALB/cJ spermatozoa, but not other tissues, showed an anomalously low level. This difference in spermatozoal β-glucuronidase activity was studied in hybrids and backcrosses but the data did not establish the number of loci affecting the difference. The levels of β-glucuronidase in F1's between C3H/HeJ and A/J depended markedly on the sex direction of the cross.
Recombination of recessivev+transformants inDrosophila melanogaster
Authors: Fox Allen S. , Kreber Robert A. , Liu Chih Ping , Yoon Sei Byung
Published: September 2009

Recessive transformants (col) obtained fromv(vermilion) embryos treated withv+DNA are shown to map at 1−0·02, a position not distinguishable from that ofsu(s) (suppressor-of-sable) and in agreement with observations indicating phenotypic allelism ofcolwithsu(s) mutants. Recombination in they–col–gtsegment of theXchromosome, over a total map length of O·3 units, was studied among the progeny ofcolv1/y1gtE6cvv1fandy1colgtE6cvv1f/v1females. The data from both crosses exhibit the following features: (1) recovery of reciprocal recombinants betweeny1andcol; (2) recovery of reciprocal recombinants betweencolandgtE6and (3) striking negative interference in they–col–gtsegment. These results allow three alternative interpretations: (1) that recombination in they–col–gtsegment results from conventional crossing-over, with high coincidence of crossovers in the two subsegments; (2) that it results from symmetrical gene conversion at thecolsite (coltocol+, andcol+tocol), which may be accompanied by single cross-overs in either of the adjacent regions; (3) thatcolbehaves like a transposable element, formally symbolizedsu(s)+·col, and that recombination insu(s)+·col/su(s)+(i.e.col/col+) heterozygotes results from transposition of thecolelement from homolog to homolog, accompanied sometimes by crossing-over, either in they–colsubsegment or in thecol-gtsubsegment.
Choline-O-sulphate utilization inAspergillus nidulans
Authors: Gravel Roy A.
Published: September 2009

The role of choline-O-sulphate (COS) as a sulphur storage compound inAspergillus nidulanswas examined by comparing a normal strain and one unable to utilize COS in a sulphur-starvation experiment designed to measure the mobilization of sulphur stores. Efforts to isolate the necessary mutants deficient in choline sulphatase activity produced two nutritionally distinct classes of mutants unable to utilize COS. They were found to be allelic on the basis of genetic complementation and fine structures mapping and represent either leaky or tight mutants with respect to choline sulphatase activity. One of these mutants with no detectable choline sulphatase activity was selected for a growth experiment which demonstrated that COS is a major, though not the only source of the endogenous sulphur supply which can be mobilized during growth in sulphur-limiting conditions.
Maternal inheritance of extranuclear mitochondrial markers inAspergillus nidulans
Authors: Rowlands Robert T. , Turner Geoffrey
Published: September 2009

Maternal inheritance of extranuclear mitochondrial genes has been demonstrated inAspergillus nidulansusing the ‘blue’ ascospore colour mutants in combination with heterokaryon incompatible strains. It appears that heterokaryosis is not a prerequisite of sexual outcrossing, and that recombination of extranuclear mitochondrial markers does not occur in the sexual stage of the cell cycle.