bluuebunny/crossref_metadata_2025 huggingface dataset:
Physiological genetics of melanotic tumours inDrosophila melanogasterVII. The relationship of dietary sterols to tumour penetrance
Authors: Cooke Jonathan , Sang J. H.
Published: September 2009

A strain ofDrosophila, homozygous for the variably penetrant genetu bw, which causes the formation of abnormal masses of melanizing haemocytes (melanotic tumours), has been reared on defined axenic diets containing various sterols, both singly and in pairs. Both optimal and deficient nutritional levels of sterol have been employed, as well as certain sterols inadequate by themselves to support development. The effect of these diets upon probability of tumour formation has been studied in relation to their nutritional adequacy, as defined by the growth-rate, survival, and in one case, adult body-weight.

The results demonstrate a rather complex pattern of interaction between dietary sterols in determining the variables of the phenotype produced, under circumstances suggesting that all the sterols investigated have entered the developing larvae. There is only a partial overall correlation, and occasionally an inverse relationship, between tumour suppressant and growth-promoting properties of particular sterols. Within single molecules, structural sterol features tend to exert their characteristic effects additively upon the phenotype, except for an inadequacy in utilization of molecules containing the Δ7double bond, which dominates at low concentrations. With pairs of dietary sterols, however, non-additive or ‘saving’ effects are sometimes seen.

It is suggested that thetu bwallele allows the resolution of several discrete developmental functions for sterols and/or their immediate metabolic products inDrosophila, which cannot synthesize its own sterol. However, the molecular nature of these functions is little understood.
The estimation of the number of mutationally silent loci in saturation-mapping experiments
Authors: Barrett John A.
Published: September 2009

When the technique of saturation mapping is employed to estimate the number of loci in a distinct chromosomal region, there is always the possibility that some loci will not be detected. If the number of mutants per locus follows a Poisson distribution, the number of mutationally silent loci can be estimated. This paper describes a method for fitting such data to a Poisson distribution truncated at the zero class and a method for estimating the number of mutationally silent loci. The use of these methods is demonstrated by their application to some published data.
Polymorphism in a varied environment: how robust are the models?
Authors: Smith J. Maynard , Hoekstra R.
Published: September 2009

This paper shows that a number of models of the maintenance of polymorphism in a heterogeneous environment, including those of Levene and Dempster, can be derived from a simple assumption about the way in which the numbers and kinds of individuals emerging from a niche depend on the number of eggs laid in it. It is shown that for such models, unless selective advantages per locus are large, protected polymorphism requires that the relative niche sizes lie in a narrow range. This lack of robustness applies also to models of stable polymorphism proposed by Clarke and by Stewart & Levin. Excluding models relaying on habitat selection or restricted migration, the only models which may escape this criticism are diploid models with partial dominance with respect to fitness, such as one proposed by Gillespie, in which in all niches the fitness of heterozygotes is higher than the arithmetic mean of the homozygotes.
Testing for rare male mating advantages among various Drosophila melanogaster genotypes
Authors: Markow T. A. , Richmond R. C. , Mueller L. , Sheer I. , Roman S. , Laetz C. , Lorenz L.
Published: September 2009

Experiments were conducted to look for minority male mating advantages among several Drosophila melanogaster genotypes. The strains of flies used were Canton-S, Oregon-R, a strain carrying the recessive mutation vermilion, and highly geo-positive and geo-negative populations which had been selected for over 200 generations in Hirsch-geotaxis mazes. Two series of experiments were carried out, one series using ten pairs of flies, and another series using 20 pairs. Regression analysis gave one significant slope out of seven, suggesting that in the present study, frequency-dependent advantages are not as common or as strong as reported for D. pseudoobscura.
The interpretation of gene conversion data from ordered eight-spored asci
Authors: Fincham J. R. S. , Hill W. G. , Reeve E. C. R.
Published: September 2009

Currently favoured models postulate that gene conversion is due to the correction of mis-matches in heteroduplex DNA. If heteroduplex is formed reciprocally on both chromatids participating in recombination, the mis-matches due to a heterozygous site will be different on the two chromatids, and there will be four correction probabilities to be taken into account. It is shown that, given the frequencies of the five different kinds of aberrant ascus ratios, it is possible to calculate four alternative sets of values for the four correction probabilities and the total number of asci in which heteroduplex is formed. These four solutions reduce in effect to two when there are no other markers distinguishing the two chromatids. With the aid of flanking markers and the assumption that heteroduplex formation is chemically polarized, it is possible, in principle, to choose one best solution.

The method has been applied to the five one-point crosses inSordaria fimicolafrom which most data are available. The data from four different mutants crossed to wild type are compatible with a restricted model in which the correction frequencies, from mutant to wild and from wild to mutant, are the same on both chromatids. In the case of the fifth mutant the data are not consistent with this restricted model, and indicate different correction frequencies in the two chromatids.
Pigmentation and lysosome function in mice homozygous for both pale ear and Beige-J pigment genes
Authors: Novak Edward K. , Swank Richard T. , Meisler Miriam H.
Published: September 2009

We have examined mice doubly homozygous for both pale ear (ep/ep) and beige (bgJ/bgJ) mutations in order to detect genetic interactions between these 2 loci affecting pigmentation and lysosome physiology. The doubly homozygous mouse has a new pigmentation phenotype consistent with independent effects ofepandbg. The beige (Brandt, Elliott & Swank, 1975) and pale ear (Novak & Swank, 1979)genes have abnormal kidney lysosomal enzyme accumulation caused by defective secretion into urine. No cumulative effect on these functions was observed in the new double mutant phenotype. The new phenotype has giant lysosomes typical of the beige mutation. Unexpectedly, the beige gene corrects the effect of the pale ear on serum lysosomal enzyme concentration. There is also a gene dosage effect of the beige gene on this serum lysosomal enzyme phenotype. The results suggest that the beige and pale ear genes affect the same pathway(s) of lysosome biosynthesis and/or processing. The action of the beige gene may precede that of the pale ear gene in lysosome physiology.
Random genetic drift in an egg-laying strain of poultry
Authors: Foster W. H. , Thompson R.
Published: September 2009

A pedigreed control strain was divided into three lines which were maintained genetically distinct over nine generations. Mean coefficients of inbreeding of about 0·1 were attained. Results suggest that discernible genetic drift had occurred in several traits. Separate estimates of genetic variance were obtained from observed variation between and within lines. These estimates differed significantly in the case of only one of the eight traits observed. Observed variation between lines agreed reasonably well with that predicted.
The kinetics of transfer of nonconjugative plasmids by mobilizing conjugative factors
Authors: Levin Bruce R. , Rice Virginia A.
Published: September 2009

A mathematical model for the kinetics of transfer of non-selftransmissible (nonconjugative) plasmids by mobilizing conjugative factors is presented and methods to estimate its parameters described. Using batch and chemostat cultures ofEscherichia coliK-12 with the nonconjugative plasmid pCR1 and an F′ mobilizing factor, the parameters of this model were estimated. The observed changes in concentrations of the different parental and transconjugant cell types and the changes in these concentrations anticipated from the model are presented for two different ‘mating’ combinations in both exponentially growing and equilibrium chemostat populations ofE. coli. The results of these experiments are interpreted to suggest that for bacterial populations dividing at a constant rate in liquid culture, the kinetics of mobilization transfer of nonconjugative plasmids can be reasonably well described by a simple set of mass action differential equations. These results also suggest that the carriage of the nonconjugative plasmid pCR1 has little, if any, effect on the capacity of a host bacterium to donate or receive conjugativeF′plasmids.
A mutant sex factor ofPseudomonas aeruginosa
Authors: Stanisich V. A. , Holloway B. W.
Published: September 2009

A mutant with the properties of a recipient has been isolated from theP. aeruginosadonor strain PAT (FP 2 + ) following treatment with the acridine-mustard ICR-191. While this strain displays the properties expected of a female or recipient in a number of genetic tests, the FP 2 determined property of mercury resistance is retained by the strain, suggesting that it may carry the FP2 factor in a mutated form. Treatment of the donor strain PAT (FP2 + ) with acridine-mustard has produced mutant male strains with the ability to form recombinants with other male strains at frequencies similar to that obtained in FP2+ × FP2 − matings. This characteristic has been shown to be due to a mutation in the FP2 factor which is dominant to the wild-type function. The isolation of stable male strains carrying both the mutant and wild type forms of the sex factor suggests that more than one copy of the FP 2 factor occurs inP. aeruginosastrain PAT donors.
The effect of an inverted chromosome segment on intragenic recombination in another chromosome ofSordaria brevicollis
Authors: Ahmad A. F. , Bond D. J. , Whitehouse H. L. K.
Published: September 2009

An inverted segment in one of the chromosomes ofSordaria brevicollishas been found to have a marked effect on recombination within a gene in another chromosome. There are two effects on the intragenic recombination pattern, namely, a change in the polarity of recombination and a change in the frequency of parental and recombinant outside markers. The results support the idea that a mechanism exists for cancelling crossovers shortly after they have been formed as a means of controlling their number.
Genetic studies on flagellum mutants ofChlamydomonas reinhardii
Authors: McVittie Anne
Published: September 2009

Eight newly isolated 9 + 0 mutants each mapped at one of the four previously known loci. Short flagellum mutants were at three loci, two of which (pf7andpf8) were closely linked; the third,pf21, was unlinked to these two and mapped on linkage group II. The long flagellum mutantslf1andlf2were on linkage groups II and XII respectively. Mutantspf8Aandlf1were both recessive to wild-type. There was no evidence for non-Mendelian flagellum mutants.
Anomalously revertible rII mutants of phage T4
Authors: Freedman R. , Brenner S.
Published: September 2009

A class of rII mutants revertible by both base analogues and acridines is described. The members of this anomalous class are base-substitution mutants suppressed by a phase-shift mutation in a phage gene mapping outside the rII region.
The integration of autonomous transmissible plasmids into the chromosome ofEscherichia coliK12
Authors: Moody Eric E. M. , Runge Richard
Published: September 2009

The highly selective technique of integrative suppression has been used to determine the ability of autonomous transmissible plasmids to integrate into theE. colichromosome.

All theF-like transmissible plasmids appear to be able to integrate, suppress the initiation defect and formHfr-type donor strains. However, there is no evidence of integration with theI-like transmissible plasmids examined.
Genetic fine structure, site clustering and marker effect in theftrcistron ofCoprinus
Authors: Moore David
Published: September 2009

Mutants in theftrcistron of the BasidiomyceteCoprinus lagopushave a lesion in sugar transport. Fifty-two alleles are placed in an allele map using recombination frequencies obtained from over 400 heteroallelic crosses. The mutant sites in the allele map are distinctly clustered into three approximately equally spaced regions. It is demonstrated that the clustering is not due to any mutational specificity. Evidence is presented which indicates that the clusters are functionally differentiated both within themselves and from one another. Additivity of recombination frequencies was good over the whole of the allele map and there was no overall map expansion. However, specific marker effect sites could be recognized. The data indicate that marker effect may act to enhance or reduce recombination frequency and that enhancement is equal and opposite to reduction. It is also shown that marker effect enhancement is only observed when the interval being mapped exceeds a certain minimum value, but that there was no upper limit to the size of the interval. Expression of marker effect was influenced both by the background genome and by the nature of the mutation at the second site in the heteroallelic cross. It is suggested that current models of recombination do not adequately explain these data and, more importantly, that then-reliance on initial breakage of DNA strands in the formation of hybrid DNA creates grave mechanical difficulties. A model for genetic recombination is proposed in which the sequence of events is: (i) separation of intact double helices into single strands; (ii) illegitimate pairing between single strands from non-sister chromatids; (iii) strand breakage and exchange of covalent links so as to legitimize the illegitimately paired regions. The model allows for the formation of hybrid DNA either with or without coincident chiasmata. It is envisaged that the error recognized by any excision-repair system involved in recombination is the tangled strands at each end of the illegitimately paired region rather than base mismatching; and that the exchange of covalent links in stage (iii) involves the excision and replacement of segments of DNA.
The hitch-hiking effect of a favourable gene
Authors: Smith John Maynard , Haigh John
Published: September 2009

When a selectively favourable gene substitution occurs in a population, changes in gene frequencies will occur at closely linked loci. In the case of a neutral polymorphism, average heterozygosity will be reduced to an extent which varies with distance from the substituted locus. The aggregate effect of substitution on neutral polymorphism is estimated; in populations of total size 106 or more (and perhaps of 104 or more), this effect will be more important than that of random fixation. This may explain why the extent of polymorphism in natural populations does not vary as much as one would expect from a consideration of the equilibrium between mutation and random fixation in populations of different sizes. For a selectively maintained polymorphism at a linked locus, this process will only be important in the long run if it leads to complete fixation. If the selective coefficients at the linked locus are small compared to those at the substituted locus, it is shown that the probability of complete fixation at the linked locus is approximately exp (− Nc), where c is the recombinant fraction and N the population size. It follows that in a large population a selective substitution can occur in a cistron without eliminating a selectively maintained polymorphism in the same cistron.
The inheritance of drug resistance and compatibility type in Phytophthora drechsleri
Authors: Khaki Ikram A. , Shaw D. S.
Published: September 2009

Methods have been developed for the selection of mutants resistant to p-fluorophenylalanine, chloramphenicol and actidione. Resistance to p-fluorophenylalanine and to chloramphenicol was inherited as if determined in each case by a single dominant allele present in diploid somatic nuclei. Inheritance of mating type was anomalous in crosses involving drug-resistant mutants. Presumptive mating-type heterokaryons were generated in a few per cent of sexual progeny from a wild-type cross.
A stable duplication of the rII region of bacteriophage T4
Authors: van de Vate C. , van den Ende P. , Symonds N.
Published: September 2009

In the preceding paper (Van de Vate & Symonds, 1974) a deletion, sdl, has been reported that stabilizes an rII diploid by penetrating into the region of the duplication from the right-hand side (if we take the rIIB gene located to the right of rIIA). Here we wish to report on a different stabilizing deletion, sd2. Evidence will be presented in favour of penetration of the duplication from the left-hand side. The right-hand terminus of the deletion is located within the rIIA gene.
Location of prophage H90 on the chromosome ofPseudomonas aeruginosastrain PAO
Authors: Carey K. E. , Krishnapillai V.
Published: September 2009

Prophage H90 has been found to undergo a phenomenon similar to zygotic induction, during conjugal transfer from a lysogenic donor to a non-lysogenic recipient.

It has not been possible to demonstrate that the level of infectious centres increases concomitantly with transfer of the prophage. However, the genetic consequence of zygotic induction was observed with regard to decreased recombinant yield of markers distal to the prophage. This latter fact has been exploited in interrupted mating experiments, to locate the prophage at between 5 and 7 min on thePseudomonas aeruginosastrain PAO map. It was further shown by transduction experiments that the prophage does not appear to be linked to clusters of co-transductional markers at the 5 and 7 min locations.
A new method of detecting centromere linkage in homothallic yeast
Authors: James A. P.
Published: September 2009

A method is described for detecting centromere linkage inSaccharomyces cerevisiaeusing a simple monohybrid for the locus in question. The method utilizes the two-spored asci produced by a normal homothallic diploid and depends upon a selective elimination of specific chromatids during spore formation. The pattern of selective elimination was not detected in a heterothallic strain but was found to be a dominant trait in an inter-strain cross. It was shown that gross chromosome aberrations are probably not responsible for the two-spored asci produced by either the heterothallic or homothallic strains.
Transmissible plasmid coding for the degradation of benzoate andm-toluate inPseudomonas arvillamt-2
Authors: Wong C. L. , Dunn N. W.
Published: September 2009

Pseudomonas arvillamt-2 (ATCC 23073) has been shown to harbour a transmissible plasmid which codes for the degradation of benzoate andm-toluate. Plasmid-borne genetic information codes for the conversion of these compounds to catechol then the assimilation of catechol via themetacleavage pathway.
Phenotypic properties of R factors ofPseudomonas aeruginosa:R factors readily transferable betweenPseudomonasand the Enterobacteriaceae
Authors: Chandler P. M. , Krishnapillai V.
Published: September 2009

R factors have been demonstrated in multiply drug resistant strains of enterobacteria andPseudomonas aeruginosain a Birmingham hospital (Lowburyet al.1969; Ingram, Richmond & Sykes, 1973). A comparative genetic analysis of these R factors has been initiated on the basis of a variety of phenotypic characteristics. This paper describes the properties of R factors derived from strains which could transfer multiple drug resistance to the recipient speciesP. aeruginosa, Escherichia coli, Shigella flexneriandSalmonella typhimurium. Two types of R factor could be recognized phenotypically. The single group 1 R factor, R18–1 which is probably the same as RPl-1 (Ingramet al.1972) was different to the group 2 R factors in many respects, including host range, R factor-specific phage plating, cellular location, drug resistance pattern, and stability. The group 2 R factors were found to be very similar to RPl (Grinstedet al.1972) and R1822 (Olsen & Shipley, 1973) with respect to their wide host range, plating of a sex specific phage, extrachromosomal location, and drug resistance pattern. Compatibility was shown between the group 1 R factor and a group 2 R factor, providing additional evidence for significant genetic differences.
Phenotypic properties of R factors ofPseudomonas aeruginosa:R factors transferable only inPseudomonas aeruginosa
Authors: Chandler P. M. , Krishnapillai V.
Published: September 2009

A study was made of the R factors from two multiply drug resistant wild type isolates ofPseudomonas aeruginosafrom a Birmingham hospital (Lowburyet al.1969) from which, in contrast to other strains from the same source (Chandler & Krishnapillai, 1974a), drug resistance was not transferable toEscherichia coliK12 orSalmonella typhimurium. Transfer of drug resistance occurred at a low frequency toShigella flexneri, although drug resistance in this species was subsequently non-transferable.

InP. aeruginosathere are several features of these two R factors which distinguish them from the group 1 and 2 R factors described previously (Chandler & Krishnapillai, 1974a). Although coding for resistance to neomycin and tetracycline, they did not express this resistance in two strains ofP. aeruginosaexamined, in contrast to the wild type strains they were isolated in.

The control of transfer of the two R factors is different to the group 1 and 2 R factors in that derepression of transfer could be demonstrated following physiological treatments or mutagenesis. The R factors of this third group were compatible with the group 2 R factors, but did not repress their pilus synthesis on the basis of R factor specific phage plating.
Linkage disequilibrium and genetic variability
Authors: Bulmer M. G.
Published: September 2009

It has been shown previously that, even in the absence of linkage, selection can cause an appreciable change in the genetic variance of a metric character due to disequilibrium; this change is temporary and is rapidly reversed when selection ceases. This result is here extended to allow for the effect of linkage, and it is shown that the change in the variance is effectively determined by the harmonic mean of the recombination fractions. The validity of the approximate general formula derived here has been checked by comparison with exact results obtained from models with five or six loci. In order to determine the likely value of the harmonic mean recombination fraction, a simple model was constructed in which it was assumed that loci are distributed at random along the chromosome maps. Results of computer simulations of this model are reported for different chromosome numbers and numbers of loci.
Chromosome banding patterns and the origin of the B genome in wheat
Authors: Natarajan A. T. , Sarma N. P.
Published: September 2009

The distribution of heterochromatic regions in the chromosomes of diploid, tetraploid and hexaploid wheat shows that the B genome possesses characteristic large blocks. Though analyses of probable B genome donors indicate thatAegilops speltoideshas a pattern of distribution of heterochromatin nearest to the B genome chromosomes, a polyphyletic origin of tetraploid wheat seems more plausible.
Methods for the isolation and analysis of plasmodial mutants inPhysarum polycephalum
Authors: Cooke D. J. , Dee Jennifer
Published: September 2009

Amoebae of the Colonia isolate ofPhysarum polycephalumproduce plasmodia within individual amoebal clones.

This paper reports the derivation from the Colonia strainC50 of a strainCL(Colonia Leicester) which produces plasmodia in clones with high efficiency and which completes the life cycle reliably and repeatedly in single clones. The derivation of a lineCLd (CLdelayed plasmodium formation) is described and, usingCLd, the construction of the isogenic heterothallic strainsmt1;CLandmt2;CL.

The above strains provide a system for the isolation and genetic analysis of mutants ofP. polycephalumwithin a uniform genetic background, in particular mutants expressed in the plasmodium.

Using this system two auxotrophic mutants have been isolated. Preliminary genetic analysis has shown that they are due to single gene mutations.
Resistance to amino acid analogues inCoprinus: Dominance modifier genes and dominance reversal in dikaryons and diploids
Authors: Senathirajah S. , Lewis D.
Published: September 2009

Wild-type strains ofCoprinus lagopusare sensitive to para-fluoro-phenylalanine and ethionine. Resistant mutants to these two analogues are known but all these mutants are recessive in a heterozygous dikaryon except for F7 (pfpr-3) which is semi-dominant. Resistance to two other analogues, however – canavanine sulphate and azetidine-2-carboxylic acid – were found to be wild-type features. One strain ofC. lagopussensitive to canavanine was identified. Selection for canavanine resistance in monokaryons always yielded only dominant resistance, while selection for para-fluorophenylalanine resistance in monokaryons gave only recessive resistance. Canavanine-resistant mutants were due to a single gene mutation which, like the wild-type resistance, were dominant in heterozygous dikaryons. The wild-type resistance was also dominant in a diploid but the mutant resistance was recessive. Selection for resistance to para-fluorophenylalanine in auxotrophically balanced dikaryons resulted in the identification of two new loci (pfpr-10 andpfpr-ll), and two specific dominance modifiers (mod+-10 andmod+-ll). In the absence of the specific modifier,pfpr-10 andpfpr-ll were recessive while, in the presence of even one dose of the specific modifier, resistance was dominant in the dikaryon. Thepfpr-10 andpfpr-ll even in the presence of two doses of modifier were fully recessive in the diploid. The action of the modifier genes and the reversal of dominance in dikaryon and diploid is discussed in terms of negative complementation in an oligomeric product of thepfprgene and localized translation of the relevant mRNA in the cell with the modifier acting as a reinforcer of localization.
Reversion studies withexrBinEscherichia coli
Authors: Greenberg Joseph , Berends Leonard , Donch John , Johnson Ben
Published: September 2009

exrBderivatives of H/r30 and WP2 are sensitive to ultraviolet radiation (UV), methylmethane sulphonate (MMS) and will not form colonies at 42 °C. Revertants to wild type were selected by plating on either nutrient plates containing MMS or nutrient plates incubated at 42 °C. Revertants selected for MMS resistance were temperature- and UV-resistant, and all revertants selected for temperature resistance were MMS and UV resistant. The frequency with which revertants appeared on MMS plates was about eight times as high as it was at 42 °C, and the variance in frequency of revertants among cultures started with small inocula was higher on selection at 42 °C than on MMS. The spontaneous frequency was estimated to be 10−6to 10−7, sufficiently low to suggest a single mutational event. Among wild-type revertants selected at 42 °C there was a stable and an unstable class.exrB+could be co-transduced withmalB+from stable revertants to anexrBstrain, but could not from unstable revertants. None of the revertants could support the growth of amber or ochre mutants of phage T4, nor were amber and ochre suppressedexrBstrains wild type with regards MMS and temperature resistance. The presence of a polarity suppressor in anexrBstrain did not modify resistance to UV or temperature. Neither UV or MMS was able to induce mutations in anexrBstrain.
Mutants affecting histidine utilization inAspergillus nidulans
Authors: Polkinghorne Meryl , Hynes M. J.
Published: September 2009

Wild-type strains ofAspergillus nidulansgrow poorly onL-histidine as a sole nitrogen source. The synthesis of the enzyme histidase (EC. 4.3.1.3) appears to be a limiting factor in the growth of the wild type, as strains carrying the mutantareA102 allele have elevated histidase levels and grow strongly on histidine as a sole nitrogen source.L-Histidine is an extremely weak sole carbon source for all strains.

Ammonium repression has an important role in the regulation of histidase synthesis and the relief of ammonium repression is dependent on the availability of a good carbon source. The level of histidase synthesis does not respond to the addition of exogenous substrate.

Mutants carrying lesions in thesarA orsarB loci (suppressor ofareA102) have been isolated. The growth properties of these mutants on histidine as a sole nitrogen source correlate with the levels of histidase synthesized. Mutation at thesarA andsarB loci also reduces the utilization of a number of other nitrogen sources. The data suggest that these two genes may code for regulatory products involved in nitrogen catabolism. No histidase structural gene mutants were identified and possible explanations of this are discussed.
Profiles of electrophoretic alleles in natural populations
Authors: Brown A. H. D. , Marshall D. R. , Albrecht L.
Published: September 2009

The charge state model of Ohta & Kimura (1973) for the number of electrophoretically detectable alleles in a finite population, is extended to include mutations of both one and two charge changes. The effective number of alleles (ne) is increased only slightly by this extension. Electrophoretic profiles of neutral variants are shown on average to be leptokurtic and have their odd central moments equal to zero. The expected frequency distribution of pairs of gametes which differ by 1,2,3,… charge units can be obtained as the sum of the appropriate terms from two geometric series.
The control of mutational instability by a new mutator gene ofDrosophila melanogaster
Authors: Woodruff R. C.
Published: September 2009

The isolation and genetic characterization of a new mutator gene,Mutator-forked3N(Mu-f3N), ofDrosophila melanogasterare described. This mutator gene is unique in that it seems to increase specifically the reversion frequency of the unstable mutantforked3N(f3N, 1–56.7), since the frequency of spontaneous sex-linked recessive lethals in males and females and the frequency of reverse mutations at eight additional X-linked alleles were unaffected byMu-f3N. The mutator is a dominant gene that has been mapped to the region betweenf3N(1–56.7) andBeadex-2 (Bx2, 1–59.4) in theXchromosome, and it seems to function only in the ‘ cis’ configuration. The mode of action ofMu-f3Nis compared with that of other mutator genes.
Constitutive heterochromatin and karyotype variation in Indian pygmy mouse, Mus dunni
Authors: Sharma T. , Garg G. S.
Published: September 2009

The Indian pygmy mouse, Mus dunni, exhibits great variation in the number of chromosome arms while its diploid number of chromosomes remains constant. The variation seems to be due to addition or deletion of C-band positive constitutive heterochromatin in the short arms of autosomes.
Unusual characteristics of the receptor for the N sex factor-specific filamentous phage IKe
Authors: Dennison Sheena , Baumberg S.
Published: September 2009

Plasmid-mediated sensitivity to filamentous phage IKe is shown to be a property exclusive to plasmids of the N incompatibility group. As with other sex factor-specific phages, IKe sensitivity results from the provision of a plasmid-encoded receptor. However, direct evidence for IKe adsorption to a sex pilus-like structure is so far lacking.

Mutations in an N plasmid were obtained which affected IKe infect-ability and N transfer frequency simultaneously, though to different extents. IKe receptors could be removed to a limited extent by high speed blending, but only under more extreme conditions (higher speed and in low ionic strength medium) than F pili. As with F-specific filamentous phages, IKe adsorption was partially blocked by Zn2+.

We tentatively suggest that the results accord with the IKe receptor being a sex pilus rather different from F and I pili (possibly in being much shorter in liquid culture), but other interpretations of these data are possible.
Altered instability due to genetic changes in a duplication strain ofAspergillus nidulans
Authors: Azevedo J. L.
Published: September 2009

Strains ofAspergillus nidulanswith a duplicate segment are mitotically unstable; they produce phenotypically improved variants following deletions in either duplicate segment, and morphologically deteriorated types. The number of variants produced is characteristic of each duplication strain under the same conditions. After ultraviolet treatment two variants, one more stable and the other less stable than the original strain, were selected. Genetic analysis showed that the increased instability in the less stable variant was due to a translocation involving linkage groups V and VIII. The increased stability of the more stable variant was due to a recessive factor (stf–1) located in linkage group VIII. In the homozygous condition this factor also reduces the number of sectors in a diploid strain. The possible genetic mechanisms explaining the instability alterations are discussed.
The inheritance of resistance to eyespot (Cercosporella herpotrichoides) in wheat
Authors: Law C. N. , Scott P. R. , Worland A. J. , Hollins T. W.
Published: September 2009

The genetic control of resistance to the fungus,Cercosporella herpotrichoides, causing the eyespot disease of wheat was studied using the Chinese Spring (Cappelle-Desprez) chromosome substitution lines andF2monosomic families of hybrids between Cappelle-Desprez and Mara. Chromosome 7A of Cappelle-Desprez was found to increase resistance to eyespot in both types of test. Chromosomes 2B and 5D of Cappelle-Desprez gave increased resistance compared to their homologues in Mara on anF2background. When substituted into Chinese Spring neither of these chromosomes appeared to increase resistance. Chromosome 1A of Cappelle-Desprez in a Chinese Spring background increased the level of infection. Dominance was towards resistance and the presence of between-chromosome interaction could be deduced.
Genetic assimilation of part of a mutant phenotype
Authors: Thompson James N. , Thoday J. M.
Published: September 2009

When the mutantveinletwas removed from aDrosophila melanogasterline selected for shortened vein length it was found that the selected polygenic background produced vein gaps in the absence of the major mutant. This example of genetic assimilation was unusual, however, in that the phenotype of the assimilated line was not exactly the same as the phenotype of the original selection line. It differed in two respects: only one of the longitudinal veins was affected in the assimilation line whereas all veins are shortened in the selectedveline, and vein gaps were sub-terminal in the assimilated line whereas they are terminal inveinlet. Modifiers of L 4 vein length were found to be located on both chromosomes II and III, though the chromosome II factor had a larger effect and was required for gap formation. The chromosome II gene was mapped to the same position as a similar L 4 vein length polygene (PL(2)L4a) found in anotherveinletselection line and reported elsewhere. The pattern of expression of thevemutant and the assimilated line genotype were compared using profiles of vein frequency at given points. The vein pattern profiles are discussed in relation to an hypothesis to explain the observed selection response and the effectiveness which these polygene combinations showed in modifying the much more complexveinletphenotype.
Selection at the alcohol dehydrogenase locus in Drosophila melanogaster imposed by environmental ethanol
Authors: Oakeshott J. G.
Published: September 2009

This paper describes selective differences imposed by environmental ethanol on six genotypes at the alcohol dehydrogenase (Adh) locus in Drosophila melanogaster. Probit analyses were used to relate differences between the percentage survival of adults of different Adh genotypes to ethanol concentration. Regression analyses were used to relate differences between the pre-adult developmental times of different Adh genotypes to ethanol concentration. The directions of differences between some of the genotypes were found to differ in these two components of fitness. The differences in developmental time are linearly related to the differences in the in vitro alcohol dehydrogenase activity expressed by these genotypes. Percentage survival differences amongst adults are not linearly related to these differences in enzymic activity. The development of AdhF AdhF pre-adults is retarded the least on ethanol impregnated media but AdhFAdhS adults are most likely to survive on such media.
Three genes determine the carboxin sensitivity of mitochondrial succinate oxidation inAspergillus nidulans
Authors: Gunatilleke I. A. U. N. , Arst H. N. , Scazzocchio C.
Published: September 2009

Partially dominant mutations to carboxin resistance occur in three, freely recombining, nuclear genes inAspergillus nidulans. Mutations at all three loci reduce carboxin inhibition of succinate dehydrogenase (EC 1.3.99.1), succinate-cytochromecreductase (EC 1.3.99.1) and succinate oxidase (EC 1.3.99.1) in mitochondrial preparations. It is therefore probable that the ability of carboxin to prevent growth ofA. nidulansis a direct consequence of its ability to prevent succinate oxidation.
Non-autonomy in achaete mosaics ofDrosophila
Authors: Claxton J. H. , Kongsuwan Kritaya
Published: September 2009

Numbers of bristles are reduced in the dorsocentral regions of achaeteDrosophila melanogaster. In achaete tissue of mosaics the effect is not uniform, and near the clone boundaries bristle numbers are significantly higher than they are elsewhere in the clone. It is argued that the cause of this non-autonomy stems from ‘factors’ that spread into the achaete clone from surrounding non-achaete cells.
Genetic analysis of morphogenetic processes in Paramecium: I. A mutation affecting trichocyst formation and nuclear division
Authors: Ruiz Françoise , Adoutte André , Rossignol Michèle , Beisson Janine
Published: September 2009

Mutation tam38 of Paramecium tetraurelia is a nuclear recessive mutation with a pleiotropic effect on both trichocyst morphogenesis and nuclear processes. The analysis of the defective nuclear processes (micronuclear and macronuclear divisions, nuclear reorganization at autogamy) shows that these defects result from an abnormal localization of the nuclei. Phenocopies of tam38 abnormalities can be obtained by vinblastine treatment of wild-type cells at late stages of division. Taking into account the similarity between tam38 and a series of other mutations which also prevent trichocyst attachment to the cell surface and disturb nuclear divisions, the following interpretation is proposed: the absence of attached trichocyst induces structural changes in the plasma membrane or in the cortical region which disturb the normal cortical control of the localization of nuclei.
Gene expression and phenotypic change inParamecium tetraureliaexconjugants
Authors: Berger James D.
Published: September 2009

A study of the patterns of phenotypic change in exconjugants using the recessive behavioural mutant pawn (pwA) and its wild-type allele shows that both cytoplasmic and nuclear factors contribute to phenomic lag. Following loss of the wild-type allele from the macronucleus, phenomic lag lasts for 6–11 cell cycles in various sublines of a single clone. Inherited cytoplasmic material is estimated to be responsible for phenomic lag of no more than 5–6 cell cycles. Longer persistence of the parental phenotype is due to continued gene activity in macronuclear fragments carrying the wild-type allele. Genes in fragments remain active and can result in maintenance of the parental phenotype as long as fragments are present (up to 11 cell cycles).

Phenomic lag in the other direction, from pawn to wild type, varies from 0 to 2 cell cycles. The major cytoplasmic factor involved is the amount of wild-type material acquired from the mate during conjugation. Extensive cytoplasmic exchange often occurs during normal conjugation and can lead to change of phenotype as early as the first meiotic division. Phenotypic change due to gene expression in macronuclear anlagen brings about phenotypic change near the end of the first cell cycle in +/+ cells and about a cell cycle later in heterozygotes.
A modifier gene involved in the expression of the dominant mating type allele inParamecium caudatum
Authors: Hiwatashi Koichi , Myohara Koji
Published: September 2009

Mating type inParamecium caudatum, syngen 3 is determined by a pair of alleles with simple dominance; the recessive allele restricts homozygotes to mating type V and the dominant allele permits expression of mating type VI. Clones of mating type V never show natural selfing, but most clones of mating type VI self naturally. A mutant clone of mating type VI which never selfed over a period of more than 3 years was obtained by treatment withN-methyl-N′-nitro-N-nitrosoguanidine. When this mutant clone was crossed to a wild-type stock of mating type V, all F1clones of mating type VI gave rise to selfers. From selfing of these F1of mating type VI, clones of F2were obtained. Nearly 3:1 segregation of selfer to non-selfer clones was observed among the F2clones of mating type VI. The results were consistent with the interpretation that a dominant modifier gene,Su(+mtV), controls the instability in the expression of mating type VI.
Quantitative predictions of random segregation models of the ciliate macronucleus
Authors: Preer John R.
Published: September 2009

Models of the macronucleus inParamecium tetraureliawhich assume known levels of ploidy and random segregation of subunits smaller than a haploid set at both fission and macronuclear regeneration (MR) are not consistent with the hypothesis that senescence is due to aneuploid imbalance. Either senescence has some other basis or there is a mechanism for regular distribution of subunits at MR. Random segregation models for fission and MR are consistent with most data on survival and heterozygote stability, but if the ploidy level is 860 they fail to account for the data of Nyberg (this volume). Since the ploidy level may be higher than 860, models of random segregation cannot be ruled out forParamecium. Models of the macronucleus in hypotrichs which assume randomly segregating chromosome fragments are consistent with data on survival and on stability of heterozygous genotypes at fission.
Gamones and mating types in the genusBlepharismaand their possible taxonomic application
Authors: Miyake Akio , Bleyman Lea K.
Published: September 2009

Mating types I and II ofBlepharisma japonicum v. intermediumexcrete gamones 1 (blepharmone J) and 2 (blepharismone) respectively. The gamone of one type transforms cells of the other type so that they can conjugate with each other. We found that three other species,B. americanum, B. musculusandB. stoltei, have two types of cells homologous to those inB. japonicum; one (type II) excretes a factor which has the same activity as gamone 2 ofB. japonicum, the other (type I) responds to this gamone by cell union. Type I cells of these species also excrete a gamone which induces pairs in type II cells of particular strains. Complementarity for mating is observed in some combinations of the two types.

These results indicate that each of the four species has at least one pair of complementary mating types, I and II, with the gamones of the type II's being the same molecule, blepharismone, while gamones of type I's are species- or syngen-specific blepharmone. These generic and specific gamones can be utilized to clarify existing taxonomic and evolutionary questions in the genusBlepharisma.
Calcium chloride effects on nuclear development inTetrahymena
Authors: Nanney D. L.
Published: September 2009

Conjugating pairs of syngen 1 exposed to 0·1 M-CaCl2during the time of macronuclear development often abort the new macronuclei and retain the old macronucleus and its associated phenotypes. The new micro-nucleus is retained, however, so that macro–micro heterocaryons can be constructed. Because the macronucleus is from a sexually mature strain, the heterocaryon is capable of mating immediately, without passing a period of sexual immaturity. Macronuclear abortion may prove a useful short-cut in genetic analysis.
Male meiotic behaviour and male and female litter size in mice with the T(2; 8)26H and T(1; 13)70H reciprocal translocations
Authors: de Boer P.
Published: September 2009

Two reciprocal mouse translocations T(2; 8)26H and T(1; 13)70H, heterozygous in a Swiss random-bred background, show differences in the spectrum of multivalent configurations and in the segregational behaviour of these multivalent configurations. T26H/+ males mostly contained rings of four (R IV, 53·15%) and T70H/+ males chains of four, missing a chiasma in the shortest interstitial segment (C IV 11, 61·55%). The adjacent II frequency, estimated from metaphase II observations, was 8·47% in T26H/+ and 25·22% in T70H/+. Univalents of the shorter translocation chromosome of T70H are able to divide equationally at first anaphase. The hypothesis is advanced that time differences in chiasma terminalization during metaphase I-anaphase are important for explaining the difference in segregation observed between the two translocations. Translocation-caused non-disjunction is probably low in T26H/+ and 4–5% in T70H/+. Univalents involving T70H/+ are usually capable of co-orientation with the other chromosomes of the translocation complex. The summed percentages of adjacent II disjunction and non-disjunction caused by the translocations were estimated from the relative fertility scores of T/+ males and females versus +/+ males and females as 9·8% and 29·0% for T26H/+ and T70H/+ males, respectively, and 9·4% and 27·8% for T26H/+ females and T70H/+ females. For both translocations, the agreement between the various estimates is good. Chiasma frequencies are much higher in telomeric segments than in proximal segments containing centric heterochromatin.
The effect of aneuploidy on meiotic crossing over and segregation in yeast
Authors: Duck P. , James A. P.
Published: September 2009

Meiotic chromosome associations in homothallic strains ofS. cerevisiaewere investigated by analysis of meiotic spore colonies and crossing over in +/+/− trisomics. The segregants of these aneuploids produce phenotypically distinguishable tetrasomic spore colonies. The data indicate that trivalent associations occur with a high frequency in trisomics of chromosome XVII and that the frequency of second division segregation is markedly increased over that found in the normal dipoid.
The effect of selection on genetic variability: a simulation study
Authors: Bulmer M. G.
Published: September 2009

Computer simulations have been done to study the effects of stabilizing and disruptive selection on a polygenic character. The results are reported in terms of three components of genetic variability which represent changes in gene frequencies, departures from Hardy–Weinberg equilibrium and linkage disequilibrium respectively. Under random mating the first and third components are the most important. The observed changes in gene frequencies are interpreted in the light of previous theoretical work on the stability of equilibria under selection. In addition, large and rapid changes in the genotypic variance result from the generation of linkage disequilibrium under selection; the observed changes are in good agreement with those predicted on theoretical grounds.