bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the mating system ofPseudomonas aeruginosastrain 1 II. Mapping of a number of early markers
Authors: Loutit J. S. , Marinus M. G.
Published: September 2009

Ten markers have been investigated for their times of entry into auxotrophic mutants ofP. aeruginosastrain 1. Using this information and unselected marker analysis two linkage groups have been demonstrated. The results could be accounted for by assuming that there were two chromosomes or that a third linkage group was involved, but we cannot distinguish between these two hypotheses at the present time.
Analysis of the genetic instability induced by nitrous acid in Schizosaccharomyces pombe
Authors: Loprieno N. , Abbondandolo A. , Bonatti S. , Guglielminetti R.
Published: September 2009

A pedigree analysis of several cell-colony generations following a mutagenic treatment with nitrous acid has shown that in S. pombe a genetic instability is produced that replicates several times and produces a mutation in independent lines.

It has been shown that the mutants isolated in the progeny of a mosaic colony all contain a genetic alteration that cannot be resolved by genetic analysis and therefore the mutations have occurred at the same genetic site. This finding is confirmed by interallelic complementation and phenotypic analyses.
Genetic studies of strain Bs8 ofEscherichia coli
Authors: Donch John , Greenberg Joseph
Published: September 2009

Strain Bs8 is a u.v.-sensitive derivative of strain B. It is unable to reactivate irradiated phage (HCR) and it cannot be induced to form filaments. The HCR properties are attributable to a gene,uvr8, cotransducible withgal+. Whenuvr8was transduced into radiation-resistant strain B/r the resulting phenotype was indistinguishable from Bs8. When transduced into alonK-12 strain the phenotype was more sensitive than Bs8, filament-inducible and mucoid. When PI-Bs8 was used to transduceproC+into aproCK-12 strain, 4% of the transductants werelon, i.e. about as u.v.-sensitive as Ion K-12, filament-inducible and mucoid. Radiation resistance could not be transduced from strain Bs8 withproC+into aproClon K-12 derivative. Nor did Bs8 show any evidence of being exr. Bs8 is a double mutant of strain B, behaving as though it were HCE, in a B/r background.
Segregation of factors controlling fusion between plasmodia of the true slime mould Physarum polycephalum
Authors: Poulter R. T. M. , Dee Jennifer
Published: September 2009

1. The occurrence of fusion between plasmodia produced from amoebal clones of P. polycephalum was studied.

2. The occurrence of fusion was found to be strain-dependent and the factors responsible segregated in the progeny of a cross.

3. The segregations found in crosses between several strains led to the conclusion that four alleles (f1–f4) of one gene f were controlling fusion in these strains.

4. Fusion occurs only between plasmodia carrying identical f alleles, except in one class of results.

5. A model accommodating all the results, including the ‘exceptional’ class, is proposed. It requires that the action of the f factors is to inhibit fusion between dissimilar strains rather than to promote fusion between identical strains. Certain physiological deductions from this model are discussed.

6. The locus (mt) determining mating type of the amoebae is not concerned in plasmodial fusion and is unlinked to f.

7. The rate of fusion between some pairs of strains is apparently influenced by modifying genes.

8. It is suggested that, as a result of the operation of the f gene and of the previously described killing reaction, heterokaryons will occur rarely in natural populations of P. polycephalum.
Resistance ofEscherichia colito penicillins: II. An improved mapping of theampAgene
Authors: Eriksson-Grennberg Kerstin G.
Published: September 2009

The first mutation step towards ampicillin resistance inEscherichia colioccurs in theampAgene, and gives resistance to a D, L-ampicillin concentration of 10 μg/ml. Using interrupted conjugation and transduction experimentsampAwas found to be located at 82 min on the time scale of Taylor & Thoman (1964). A number of adjacent markers were studied and the probable gene order of theampAregion was found to beargH-metA-uvrA-ampA-purA-fdp-pyrB. Two independent alleles ofampAwere cotransduced withfdp+andpurA+. The phenotypic expression ofampAin apurAstrain has been investigated.
Resistance ofEscherichia colito penicillins: III. AmpB, a locus affecting episomally and chromosomally mediated resistance to ampicillin and chloramphenicol
Authors: Nordström Kurt , Eriksson-Grennberg Kerstin G. , Boman Hans G.
Published: September 2009

We have previously described strains ofEscherichia coliK12 resistant to D, L-ampicillin concentrations of 50 μg/ml (Eriksson-Grennberget al.1965; Bomanet al.1967). Such strains were assumed to be double mutants carrying the genesampAandampB. We here describe genetic steps which produce strains carrying only theampBgene. Determinations of resistance showed thatampAincreased the resistance provided byampA+by a factor of 10–15.AmpBincreased the resistance of bothampAandampA+by a factor of 2.

R-factors were introduced into two sets of strains with all combinations ofampA,ampBand their wild type alleles.AmpAand the R-factors gave additive effects on resistance, whileampBdoubled the ampicillin resistance mediated byampAas well as by the R-factors.AmpBalso enhanced the chloramphenicol resistance of R-factor and of the wild type chromosomal genes. It is suggested thatampBresembles the modifying genes previously described and that R-factors can be useful for the identification of such genes.
The effects of dark holding and photoreactivation on ultraviolet light-induced mitotic recombination and survival in yeast
Authors: Parry James M. , Cox B. S.
Published: September 2009

UV induces lesions in DNA which lead to the death of cells, mutation and, in yeast, intragenic and intergenic mitotic recombination. We have investigated the interaction of two post-treatments, dark holding and photoreactivation, on the frequencies of these events. It was found that dark holding reduces cell death and intergenic recombinants, but causes an increase in intragenic recombination frequency. Photoreactivation reduces cell death and intragenic recombination, but has no effect on intergenic recombination. After dark holding, photoreactivation has no further effect on cell survival or intergenic recombination, but may reduce the frequency of intragenic recombinants. After photoreactivation, dark holding still causes an increase in cell survival and the frequency of intragenic recombination, and reduces the frequency of intergenic recombination.
The effects of population size and selection intensity in selection for a quantitative character inDrosophila: III. Analyses of the lines
Authors: Frankham R. , Jones L. P. , Barker J. S. F.
Published: September 2009

1. In order to determine the nature of the genetic variation causing the response to selection in our lines (Joneset al.1968), various analyses were performed.

2. There was no consistent change in heritability, estimated from half-sib correlation or from the phenotypic correlation between the bristle numbers of two abdominal segments, after 10 to 20 generations of selection.

3. Realized heritabilities over the 10 generations subsequent to the heritability estimations were less than in the early generations but bore little relationship to the estimated values.

4. Six lines contained recessive lethals with appreciable effects on bristle number as indicated by high variances, large regression on relaxation and large response to reverse selection.

5. Reverse selection lines taken from the main lines at generation 40 indicated that genetic variation was still present in almost all of the lines. Only one line failed to respond to further forward or to reverse selection.

6. The three highest lines were crossed in pairs and reselected. Two of the three possible crosses gave further response, exceeding the higher parent after one and three generations, but the other cross failed to pass the highest parent line.

7. A combination of large gene effects, linkage, and gene interaction effects have been suggested as the cause of irregularities in the response of the lines. It has not been possible to determine the relative importance of these effects.
The genetics of the Xasta mutant ofDrosophila melanogaster
Authors: Hetherington C. M. , Whittington W. J. , Hossain M. A. , Peat W. E.
Published: September 2009

Xasta flies appear to segregate five types of gametes in unequal numbers, namely two which contain both or neither of the chromosomes affected by the translocation and inversions, two further classes which contain one affected and one unaffected chromosome, and finally the remainder which have an unbalanced chromosomal content. These conditions are necessary to fit the results observed in crosses involving the Xasta stock. Xasta exhibits balanced polymorphism under crowded conditions and this may be due to the production of toxic substances byXalarvae which delay the development of wild type-larvae.
Cytogenetic studies ofN Lc1yg2R2marker genes and chromosome deficiences in cotton
Authors: Endrizzi J. E. , Taylor T.
Published: September 2009

A monosome was identified as chromosome 7 of the A genome of the tetraploid cottons by its linkage with theLc1yg2R2markers. This makes eight chromosomes of the tetraploids now identified by monosomes. For over a decade theNlocus has been considered to be linked with theLc1yg2R2loci. Monosomic analysis, however, reveals thatNis on a separate chromosome. Studies with a telocentric of chromosome 7 show that theLc1yg2R2loci are located in the long arm. It is suggested that theR2locus rather than theLc1locus is in the proximal position. These findings are discussed in relation to data, particularly that involving the linkage group, which supposedly illustrate the compensatory recombination phenomenon in cotton.
Further evidence for coadaptation in crosses between geographic populations ofDrosophila pseudoobscura
Authors: Anderson Wyatt W.
Published: September 2009

Body size inDrosophila pseudoobscurais a continuously varying character with a high heritability; it is almost certainly related to fitness. Natural populations ofD. pseudoobscurafrom Canada to Mexico have been sampled and found to vary geographically in body size. The geographic variation for the genes determining size is to some extent correlated with the physiographic division of the West. The populations from the Pacific coast have genetically smaller flies than do those from the interior provinces. Experimental populations derived from the samples of seven widely separated natural populations were crossed to yieldF1andF2hybrid generations. Body size in theF1's varied irregularly, while theF2's showed a consistent ‘breakdown’, theF2's being significantly smaller than theirF1parents. TheF1's were significantly less variable than their parents, while theF2's were significantly more variable than their parents of theF1generation. The natural populations possess coadapted genetic systems, with genes mutually adjusted by selection for favorable interactions. Recombination disrupted the balanced genic complexes to give theF2breakdown and the increasedF2variability.D. pseudoobscuradiffers fromD. subobscurain showing the effects expected in crosses between coadapted systems. This species difference lends additional support to the hypothesis that the gene pools of these two successful species respond in different ways to environmental variation. The gene pool ofD. pseudoobscurais flexible and changes readily, while that ofD. subobscurais relatively rigid.
The relation between virus-like particles and R bodies of Paramecium aurelia
Authors: Preer John R. , Jurand Artur
Published: September 2009

Virus-like particles can be seen in sections of kappa of stocks 7 and 562. The virus-like particles are specifically associated with R bodies and are rare or absent in kappa particles lacking R bodies. This observation clearly links the virus-like particles with kappa's toxic activity; it also supports the suggestion that kappa is infected with a lysogenic virus whose induction results in the production of the R body and viruses. Many ‘unfilled’ virus-like particles are present in whole kappa particles. Wound R bodies of stock 7 are surrounded by a sheath, whose breakage may provide the mechanism which causes the unrolling of the R body. One edge of the R body ribbon stains more intensely than the other.
Drug sensitivity and mutability to drug resistance associated with the presence of an R factor
Authors: Yoshikawa Masanosuke
Published: September 2009

Studies on the growth kinetics of R+and R−cultures ofEscherichia coliin the presence of nalidixic acid (NA), acriflavine (AF) and kanamycin (Kan) showed that each drug caused a decline in viability of both R+and R−cells for several hours. During further incubation the viability rose rapidly for the R+cultures, but either rose less rapidly (AF and Kan) or continued to decline (NA) for R−cultures. Distribution curves of the resistances of individual clones of R+and R−bacteria to atabrine, NA, AF and Kan suggested that the presence of an R factor in the host bacterium increased its mutation rate to resistance to these drugs: this would account for the more rapid growth rate of R+cells during the latter stages of incubation in their presence. The mutations causing increased resistance to NA and to Kan were located in the bacterial chromosome and not in theRfactor.
Interaction of a colicinogenic factor with a resistance factor and with the fertility factor F inEscherichia coliK-12
Authors: Cooper Pearl
Published: September 2009

The resistance (R)-factor R538–1drdof three F-like R-factors tested can cause the transfer of the non-transmissible ColV determinant fromE. coliV. The col factor, once transferred toE. coliK-12 strains, was shown to be related to the fertility factor, F, on the basis of entry exclusion and plasmid incompatibility. The col factor was found to recombine with R538–1drd, yielding a transmissible plasmid comprised of the col determinant and the sex factor of the R-factor, but not the resistance genes. The recombinant plasmid was found to be incompatible with both R538–1drdand F, and excluded the entry of R538–1drdbut not F.
Conditional induction ofλprophage inexrAmutants ofEscherichia coli
Authors: Donch J. J. , Green M. H. L. , Greenberg J.
Published: September 2009

Strains ofEscherichia coliwhich contain the UV sensitivity geneexrA, repress UV induction ofλprophage in a novel manner. WhileexrA+strains can be induced by UV irradiation and express this induction in a 2 h period,exrAmutants delay the expression of induction for almost 4 h, and the induction maximum is approximately 10% of the wild-type value. The kinetics of the delayed induction and superinfection experiments indicate that the lifting of immunity and induction ofλprophage occur simultaneously.
Genetical evidence for diploidy in Phytophthora
Authors: Shaw David S. , Khaki Ikram A.
Published: September 2009

A spontaneous mutant of Phytophthora drechsleri, resistant to p-fluorophenyl-alanine and two induced mutants resistant to chloramphenicol have been selected and analysed. The pattern of inheritance of the mutant phenotypes was identical and conformed to that expected in a diploid organism.
Chromosome transfer inPseudomonas aeruginosamediated by R factors
Authors: Stanisich Vilma A. , Holloway B. W.
Published: September 2009

R factors present inPseudomonas aeruginosastrains of clinical origin can be transferred to other strains ofP. aeruginosaand may act to promote host chromosome transfer. In general, their properties are similar to those R factors in Enterobacteria. The different R factors studied vary with respect to transferability, transfer of specific resistance properties, repressibility, and ability to promote chromosome transfer.
The physiological control of gene action in theeyelessandeyegonemutants ofDrosophila melanogaster
Authors: Hunt David M.
Published: September 2009

The effect of dietary supplements of individuall-amino acids on the expression of theeyegoneandeyelessKmutants ofDrosophila melanogasterare compared. In both mutants, eye size is reduced by excess levels of tryptophan, phenylalanine and methionine, and in each case the effects are independent of metabolic competition for pyridoxal phosphate. A dietary interaction involving methionine and UNA can be demonstrated in theeyKstrain, but the mechanism of action of this amino acid is obscure. Tryptophan metabolism is examined in detail. Although both tryptamine and serotonin have significant effects, the action of tryptophan on eye development is largely independent of its metabolic products. Conversely, the effect of dietary supplements of certain catecholamines is consistent with the action of phenylalanine. The action of certain metabolic inhibitors provides additional support for the suggestion that the catecholamines have an important effect on morphogenesis in the eye imaginai disks. Eye development is also affected by increasing concentrations of γ-amino-butyric acid, and this, taken together with the effect of the catecholamines and indolalkylamines, suggests that physiological control of the action of the mutant genes on eye development involves a group of compounds characteristically associated with nervous tissue. Eye development in theeyKstrain may be influenced by the availability of acetyl CoA, which would be expected to affect acetylcholine biosynthesis. Possible mechanisms of action of the effective dietary treatments are discussed, together with a tentative hypothesis regarding the mode of action of the mutant genes on eye development.
The production and assay of segmental substitution lines in barley
Authors: Gale M. D. , Rees H.
Published: September 2009

The usual systems of assay using techniques of chromosome substitution demonstrated inDrosophilaand wheat are not applicable to barley (Hordeum vulgare). Chromosomal material for assay may, however, be substituted from one variety into another by using translocations to mark and restrict crossing over in the chromosomes to be transferred. This paper describes the isolation and assay of lines derived in this way.

Seven substitution lines derived from the donor variety Maris Badger and the recipient variety Mars have been scored for quantitative characters in two field trials.

The results indicate that variation in flowering time and other associated characters is largely determined by genes on chromosome 2 and that chromosome 4 is involved in the control of plant height.

The feasibility of the technique as a method of assaying the contributions of chromosomes to qualitative characters by substitution in a diploid is discussed.
The microscopic appearance of waved-2 mouse hairs
Authors: McLaren Anne
Published: September 2009

Hairs from two stocks of homozygous waved-2 mice have been examined. The observations do not agree with a previous report, that the waving was due to a decrease in the proportion of guard hairs and an increase in the number of constrictions per hair, but are consistent with the view that it arises from a defect of keratinization.
Transduction mechanisms of bacteriophage ε15I. General properties of the system
Authors: Hedges R. W.
Published: September 2009

Bacteriophageεγis capable of transduction both by replacement of a genetic segment of the recipient by the homologous genetic material from the donor strain and by the formation of defective transducing particles capable of lysogenizing the recipient strain ofS. anatum.

The isolation of strains carrying such prophages, which have incorporated the lactose or arabinose operons, is reported. Lysogenic strains, carrying both normal and defective transducing prophage, form high-frequency transducing lysates. Other strains, carrying only defective prophage, show evidence that the association of prophage genes and transduced materials is stable since the loss of one frequently entails loss of the other.
Spirochaete-mediated abnormal sex-ratio (SR) condition in Drosophila: A second virus associated with spirochaetes and its use in the study of the SR condition
Authors: Oishi Kugao
Published: September 2009

A class of abnormal sex-ratio (SR) condition in Drosophila characterized by the elimination of male zygotes is caused by infection with maternally transmitted SR-spirochaetes. A given spirochaete strain, WSR, was shown to have an associated DNA virus, spv-2, in a latent condition. This virus is induced to multiply when another DNA virus, previously designated spv-1, infects WSR spirochaetes; spv-1 is normally associated with another strain of SR-spirochaetes, NSR, and is in a manifest state. Spv-2 infects and lyses NSR, thus eliminating spirochaetes from fly hosts which, in these experiments, were D. melanogaster.

The elimination of WSR through lysis by spv-1 results in the ‘curing’ of the SR-condition in the host flies. However, the elimination of NSR by spv-2 does not lead to the immediate elimination of the SR-condition in the host. A hypothesis is presented in favour of the view that a substance, androcidin, is produced by SR-spirochaetes and that this substance is actually responsible for the death of male zygotes. NSR may produce a more potent androcidin than WSR.
A purine and pyrimidine requiring mutant ofDrosophila melanogaster
Authors: Vyse E. R. , Sang J. H.
Published: September 2009

The E.M.S.-induced auxotrophic mutant1308ofDrosophilais located between 13·7 and 21·0 on chromosome 1. Survival of larvae is possible if whole RNA is provided in the diet, and this is shown to be a requirement for a source of both purines and pyrimidines. A proportion of larvae will grow on pyrimidine nucleosides alone. Tests for utilization of bases and of precursors suggest that1308is a double mutant, and not a single mutation preventing the synthesis of a common precursor of purines and pyrimidines.
Phosphatases ofCoprinus lagopus: the conditions for their production and the genetics of the alkaline phosphatase
Authors: North Jane , Lewis D.
Published: September 2009

1.Coprinus lagopusproduces two non-specific phosphatases: a constitutive acid phosphatase, and an alkaline phosphatase which is repressed during growth on media with a high inorganic phosphate concentration.

2. The alkaline phosphatase is also repressed whenCoprinusis grown on an organic phosphate source; but if the acid phosphatase is selectively inhibited by fluoride the alkaline phosphatase is de-repressed and growth is comparable to that observed on an inorganic phosphate source.

3. Alkaline phosphatase is not repressed in aerial mycelium or sporophores even when grown on high phosphate medium.

4. Mutants altered in their capacity to synthesize alkaline phosphatase were selected from two compatible wild-type strains, H2 and H5.

5. Mutants producing a higher level of alkaline phosphatase than wild-type (‘regulator’ mutants) fall into four (or possibly five) complementation groups. Assuming five separate genes, two pairs are linked; the remaining one is independent and on another chromosome.

6. Mutants deficient in alkaline phosphatase synthesis fall into at least three groups. They were tested for linkage to ‘regulator’ loci but so far there is no evidence of this.
Phenotypic specificity of aneuploid states inAspergillus nidulans
Authors: Upshall A.
Published: September 2009

Hyperhaploid and hyperdiploid colonies ofAspergillus nidulans, disomic or trisomic for one or more chromosomes respectively, are abnormal in phenotype and somatically unstable. It has been shown for Glasgow strains that a different specific phenotype arises, depending upon which chromosome is additional (Pollard, Käfer & Johnston, 1968). This report extends this system and shows that irrespective of the residual genetic background of the isolate, the system of phenotypic specificity applies.
R-Factor elimination by thymine starvation
Authors: Pinney R. J. , Smith J. T.
Published: September 2009

R-factor 1818, which is refractory to curing by acridines or ethidium bromide fromEscherichia coliK 12 andKlebsiella aerogenes418 hosts, was eliminated from thymineless mutants of these organisms under conditions of thymine starvation. Neither R-7268 nor R-TEM could be eliminated by this method. The concurrence of R-TEM with R-1818 inhibited the curing of R-1818, whereas R-7268 had no effect on R-1818 elimination
Genetic analysis of spontaneous half-sectored colonies ofSaccharomyces cerevisiae
Authors: Johnston J. R.
Published: September 2009

Genetic analysis of spontaneous half-sectored colonies of a diploid strain homozygous forade2and heterozygous for linked markersaro1A,hom2,ade8 and trp4was undertaken. Some of these were due to an unexpectedly high rate ofade2reversion and others to a low incidence of haploid sectors. About 50% resulted from mitotic recombination. Only a few were due to mitotic crossing over alone, the majority resulted from non-reciprocal ‘conversion’, including recombination extending over two loosely-linked loci, and some colonies featured both mitotic crossing over and mitotic conversion. The latter indicate that negative interference operates for mitotic recombination. The rate of mitotic recombination forade8, calculated from the frequency of half-sectored colonies was 3·1 × 10−4per cell division.
Meiotic disjunction in mouse translocations and the determination of centromere position
Authors: Searle A. G. , Ford C. E. , Beechey C. V.
Published: September 2009

If heterozygotes for a reciprocal translocation are intercrossed, some of their viable balanced progeny result from the fusion of unbalanced gametes with complementary duplications and deficiencies of the translocated segments. Therefore, if one parent in such an intercross is homozygous for a genetic marker on one of the segments concerned, some homozygous offspring will be produced even if the other parent does not have the marker. The expected frequency of such exceptional offspring among live-born is one-sixth if the marker is on the distal (non-centromeric) side of the point of exchange and single chiasmata normally occur in each interstitial segment. Much lower frequencies are expected if the marker is on the centromeric side, since duplications and deficiencies of proximal segments occur only as a consequence of adjacent-2 disjunction, in which homologous centromeres proceed to the same pole. This is rarer than normal disjunction. Thus, by comparing the frequencies of offspring homozygous for markers on one or other side of the point of exchange, it is possible (i) to determine which marker is in the centromeric segment, (ii) to estimate the frequency of adjacent-2 disjunction, given information on the nature of meiotic configurations in the translocation concerned.

By this method, it is shown that the frequency of adjacent-2 disjunction is similar in heterozygotes for mouse translocations(T5;18)26H, T(13; ?) 70HandT(14;17)264Ca, averaging 13%. Centromeres were located at theSdend of linkage group V (confirming previous findings), thefzend of XIII and the bg end of XIV.
The genetic control of anthocyanin biosynthesis by homoeologous chromosomes in wheat
Authors: Gale Michael D. , Flavell Richard B.
Published: September 2009

Coleoptile anthocyanin pigmentation in the hexaploid variety of wheat, Hope, is due to at least eight anthocyanins including four acylated forms. All are derivatives of either cyanidin or peonidin. Two homoeologous chromosomes, 7A and 7B, are involved in anthocyanin production. Both chromosomes carry genes that promote the synthesis of the same anthocyanins from flavonoid precursors. The roles of chromosomes 7A and 7B in anthocyanin biosynthesis and the consequences of interallelic interaction and dominance of possibly homoeologous loci are discussed.
Some details and effects of the premeiotic controls of recombination frequencies inNeurospora crossa
Authors: Lamb B. C.
Published: September 2009

Recombination data from crosses made at a single constant temperature of incubation were compared with those from crosses transferred to a different temperature at either the time of conidiation of protoperithecia by the strain of opposite mating-type, or after fertilization when crozier stages were first visible. Results were also compared from reciprocal crosses, from crosses made in different ways and from crosses in which protoperithecia were conidiated at different stages of maturity.

Different temperature regimes during vegetative growth and proto-perithecial development had highly significant effects on subsequent meiotic recombination, while temperature differences during later premeiotic stages (between conidiation of protoperithecia and the crozier stage) had no or little effect. It was found that premeiotic controls could have as great, or greater, effects on meiotic recombination than those operating directly during meiosis. The possible adaptive significance of this is discussed.

Recombination frequencies were affected by the method of making a cross (joint-inoculation of strains of opposite mating-type, or conidiation of protoperithecia), and by protoperithecial age at the time of conidiation by the opposite mating-type. Differences in recombination between reciprocal crosses were obtained and were dependent on temperature of incubation and age of protoperithecia at the time of conidiation. Recombination was not affected by different lysine concentrations in the medium. Genetic differences in premeiotic effector-production between the strains used were inferred.
Inactivation of whole chromosomes in mammals and coccids: some comparisons
Authors: Chandra H. Sharat
Published: September 2009

Genetic systems involving developmental inactivation of entire chromosomes occur in two widely different groups of organisms: mammals and coccids (Homoptera: Insecta). The two groups show several similarities and some interesting contrasts with respect to this unusual cytogenetic phenomenon. Although mammalianXchromosomes and coccid paternal sets are components of different genetic systems, comparisons between them nevertheless suggest approaches that might prove to be of value. Further, the occurrence of facultative heterochromatization in these two wholly unrelated taxa must mean that this type of heterochromatization represents a fundamental capacity of chromosomes.
Associative overdominance caused by linked detrimental mutations
Authors: Ohta Tomoko
Published: September 2009

Associative overdominance due to linked detrimental mutations was investigated using the method of moment equations based on diffusion models. The expectation of the apparent selective value at the marker (neutral) locus has been evaluated. Assume two linked loci, at one of which the steady flux equilibrium is reached under constant mutational input of deleterious mutations (with ratev) having disadvantageshsin heterozygote andsin homozygotes. At another locus, the neutral alleles are segregating with frequencies near 0·5. Let Nebe the effective size of the population andcbe the recombination fraction between the two loci. Then the coefficient of associative overdominance at the neutral locus can be obtained by taking the expectation with respect to chromosome frequencies at steady flux equilibrium. It becomes approximately

where (LI−L0) is the inbreeding depression caused by deleterious mutations under complete inbreeding, andNehs≫ l andhs≫vare assumed. More generally, if the inbreeding depression of a chromosome segment with a length of recombination fraction C is (LI−L0) then s′ at the neutral marker at the edge of the segment is

wherehsis the average heterozygote disadvantage of detrimentals.

The significance of the associative overdominance is discussed in relation to actual observations. It is proposed that the most of the observed heterozygote superiority including inversion chromosomes ofDrosophila, isozyme alleles inAvenaand ABO blood group genes in man could be explained by the associated detrimentals.
Recombination and complementation between R factors inEscherichia coliK 12
Authors: Foster T. J. , Howe T. G. B.
Published: September 2009

Recombination between chloramphenicol-sensitive (Cms) mutants of Rl, and R100, has been demonstrated inEscherichia coliK12rec+; it occurs at reduced frequency inrecBandrecC, and is not detectable inreeA, indicating that R factor recombination depends on host functions. Some mutants of R1 also recombine with an R100 mutant in a similar way.recAcells carrying an R1 and an R100 Cmsmutant (hetero-R state) have a low level of chloramphenicol-resistance, and form a chloramphenicol acetyl transferase that has lower specific activity than enzyme from hosts carrying wild-type or recombinant factors. These results suggest the occurrence of interallelic complementation between mutant R factors.
p–Fluorophenylalanine-induced mitotic haploidization inUstilago violacea
Authors: Day A. W. , Jones J. K.
Published: September 2009

Haploid segregante from vegetative diploids ofUstilago violaceaappear as spherical colonies (papillae) growing above a background of dead diploid cells on complete medium containing DL-p–fluorophenylalanine (PFP). Most mutants segregate normally but one-third of the mutants were expressed infrequently in 0–5% papillae only. These mutants, designated ‘missing-markers’, were found to be on either of two chromosomes that remained disomic after treatment with PFP. When cells from a disomic papillum were streaked on complete medium, monosomics in which ‘missing-markers’ were expressed segregated spontaneously at a low frequency. Thus, of 10–12 linkage groups identified inU. violacea, two remain disomic after PFP treatment. Possible reasons for these differences between chromosomes in the same genome are discussed.

Haploid and diploid stock cultures did not differ either in resistance to PFP, or in the production of papillae on PFP medium. Haploid segregante from a diploid were slightly more resistant to PFP than the wild-type haploid cultures under some conditions, but were very different in that they no longer produced papillae on PFP medium. These haploid segre-gants resembled one of three PFP-resistant mutants (pfp-A) isolated from a wild-type haploid stock grown on PFP medium. The significance of these results to the mechanism of haploidization inU. violaceais discussed.
The position of a locus on chromosome 5B ofTriticum aestivumaffecting homoeologous meiotic pairing
Authors: Wall A. M. , Riley Ralph , Gale M. D.
Published: September 2009

An investigation was made of the chromosomal position of the mutant locus, in Mutant 10/13 ofTriticum aestivum(2n= 6x= 42), affecting homoeologous chromosome pairing at meiosis. In hybrids between Mutant 10/13 and rye (Secale cereale2n= 14), homoeologous chromosomes frequently pair at meiosis although normally, in wheat-rye hybrids, this happens infrequently.

The association of the mutant condition with chromosome 5B was determined by (i) the absence of segregation in hybrids obtained when Mutant 10/13 monosomic 5B was pollinated by rye; (ii) the occurrence of trisomie segregation for pairing behaviour in 28-chromosome wheat-rye hybrids, obtained from SB trisomie wheat parents with two 5B chromosome from a non-mutant and one from a mutant parent; (iii) the absence of segregation for pairing behaviour in the 29-chromosome wheat-rye hybrids obtained from the same trisomie wheat parents.

The alternative pairing behaviours segregated independently of the centromere when wheat plants that were simultaneously heteromorphic, 5BLtelocentric/5B complete, and heterozygous for the Mutant 10/13 state, were pollinated by rye. The alternative chromosome-pairing patterns segregated to give a ratio not different from 1:1, so that the association of homoeologous pairing with Mutant 10/13 probably derived from the occurrence of mutation at a single locus on 5BL. In the disomic heteromorphic state, 5BLwas 91 map units in length.

Trisomie wheats with two complete 5B chromosomes and one 5BLtelocentric, that were also heterozygous for the Mutant 10/13 condition, were pollinated by rye. Among the resulting 28-chromosome hybrids there was a 2:1 segregation of hybrids with low pairing: high (homoeologous) pairing and also of hybrids with complete 5B: telocentric 5BL. However, there was no evidence of linkage in this trisomie segregation. All the 29-chromosome hybrids from this cross had low pairing and it could be concluded that the single mutant allele, in Mutant 10/13, was recessive. In the trisomie condition, relative to a simplex situation, 5BLwas 33·05 map units in length.

The critical locus on 5BLwas designatedPairing homoeologous. The normal dominant allele was symbolizedPhand the recessive allele, in Mutant 10/13,ph.

The prevention of homoeologous pairing by the activity of a single locus makes the evolution of the regular meiotic behaviour ofT. aestivummore readily comprehensible.
Two-environment selection with inbreeding inSchizophyllum commune
Authors: Connolly V. , Simchen G.
Published: September 2009

In two-way selection for growth rate in the fungusSchizophyllum communein two environments (20 °C and 30 °C) response for low growth rate was always greater than for high. This asymmetry was due to inbreeding depression combined with a greater selection differential associated with the low lines in the high temperature environment. Despite the high level of inbreeding applied, two low selection lines derived from the same source (parental isolate 2) showed no decrease in genetic variance during selection. This maintenance of genetic variance was associated with a decrease in stability of development relative to the corresponding high selection lines.
Bare-patches, a new sex-linked gene in the mouse, associated with a high production of XO females: I. A preliminary report of breeding experiments
Authors: Phillips Rita J. S. , Hawker S. G. , Moseley H. J.
Published: September 2009

Bare-patches (Bpa), a semi-dominant, sex-linked, male-lethal gene in the mouse is described. It shows 14·5 ± 3·0% recombination with Blo and 5·4 ± 2·2 % with Ta and may, therefore, be allelic with Str.

Only about half the expected number of heterozygous females is observed; the remainder appear to lose their mutant chromosome and become XO females as there is an excess of non-Bpa females, at least 24% of which proved to be XO. It is not yet certain whether the lost X chromosome is always the mutant one nor is it certain whether the loss is a property of the Bpa gene or due to a closely linked factor: a separate factor seems more likely. Some possible mechanisms for XO production are discussed.
Corresponding-site interference, synaptinemal complex structure, and 8+:0mand 7+:1moctads fromwild-type×mutantcrosses ofAscobolus immersus
Authors: Lamb B. C. , Wickramaratne M. R. T.
Published: September 2009

‘Wider ratio’ octads (8:0, 0:8, 7:1 and 1:7) regularly occurred inwild-type(+) ×whiteascospore(w) crosses of the Pasadena strains ofAscobolus. Control crosses showed that phenocopies and false octad clusters were absent or rare; no reversion fromwto + occurred, but mutation from + towwas found at a number of loci, with nearly all 0+:8wand many 2+:6woctads in + ×wcrosses arising from mutation, not conversion. Nearly all 8+:0w, 7+:1wand 6+:2woctads appeared to arise by conversion.

The finding of genuine wider ratio octads implies hybrid-DNA formation at corresponding sites inbothpairs of non-sister chromatids in the same bivalent, which conflicts with models of the synaptinemal complex requiring that only two of the four chromatids pair intimately at any point. Octad types arising from hybrid-DNA formation at corresponding sites in both pairs of non-sister chromatids were described and formulae were derived for their frequencies. The lack of genuine wider ratio octads in several otherAscobolusstudies was shown to be explicable quantitatively in terms of their conversion frequencies.

‘Corresponding-site interference’ is defined as interference between the two pairs of non-sister chromatids of a bivalent in hybrid-DNA formation at exactly corresponding sites. Formulae based on observed octad frequencies were derived for calculating coincidence values for this kind of interference. Corresponding-site interference was found to be weak, with coincidence values differing between crosses with high and with low conversion frequencies.
Further studies on the maintenance of mate-killer (mu) particles in Stock 540Paramecium aurelia
Authors: Franklin J.
Published: September 2009

1. Mu particles can be removed from stock 540Paramecium aureliaby incubation in a solution of 1·0 mg/ml RNAase for 12 h. Only a relatively small percentage of cells become mu-free and it is suggested that this variation is due to the activity of the M genes producing metagons at different times.

2. Paramecia, made mu-free by growth at elevated temperatures, can be re-infected with mu by allowing the cells to swim in a brei of stock 540 paramecia. The re-infection is only permanently successful with cells that were made mu-free 10 days earlier.
The position on chromosome 5B of wheat of the locus determining crossability with rye
Authors: Lange Wouter , Riley Ralph
Published: September 2009

The allelekr1, conditioning ready crossability between wheat and rye when wheat is the female parent, is at a locus already known to be on chromosome 5B of wheat. This locus was mapped using a telocentric chromosome consisting of the long arm of chromosome 5B. Mapping was carried out by analyses ofF2and testcross progenies. The two experiments gave a mean recombination frequency, between the locus and the centromere, of 11·45 ± 3·0%. The possibility of different recombination frequencies in male and female meiosis is discussed.
Variability of recombination frequencies in theftrcistron ofCoprinusand its influence on the identification of marker effect alleles
Authors: Moore David
Published: September 2009

The variability of recombination frequencies between alleles of theftrcistron is assessed and shown to be normally in the range of ± 25% though occasionally replicates differed by a factor of two and in rare cases even more extremely. It is shown that the variation results from biological differences between separate attempts at the same cross and cannot be ascribed to sampling error or any other controllable cause. In the light of this variability the marker effect alleles already recognized in this cistron are re-examined with a new series of crosses. It is confirmed that marker effect may act to enhance or reduce the recombination frequency but it is shown that enhancement can be expressed in two entirely different ways. There is one type of site which causes a uniform doubling of the recombination frequency in all crosses no matter where the second site is placed in the map. The second type of marker effect enhancement site causes a very great increase in recombination frequency in crosses against relatively closely linked mutants, but its effect diminishes as the distance between the marker effect site and the second site is increased.
A model of mutation appropriate to estimate the number of electrophoretically detectable alleles in a finite population
Authors: Ohta Tomoko , Kimura Motoo
Published: September 2009

A new model of mutational production of alleles was proposed which may be appropriate to estimate the number of electrophoretically detectable alleles maintained in a finite population. The model assumes that the entire allelic states are expressed by integers (…,A−1,A0,A1, …) and that if an allele changes state by mutation the change occurs in such a way that it moves either one step in the positive direction or one step in the negative direction (see also Fig. 1). It was shown that for this model the ‘effective’ number of selectively neutral alleles maintained in a population of the effective sizeNeunder mutation rate υ per generation is given by

When 4Neυ is small, this differs little from the conventional formula by Kimura & Crow, i.e.ne= 1 + 4Neυ, but it gives a much smaller estimate than this when 4Neυ is large.
Mutants of Coprinus selected for resistance to D-glucosamine and L-sorbose
Authors: Moore David
Published: September 2009

Mutants resistant to growth inhibition have been obtained by selecting on media containing inhibitory concentrations of either d-glucosamine or l-sorbose. All of the mutants isolated were found to be sugar transport-defective and cross-resistant to growth inhibition by the three analogues 2-deoxy-d-glucose, d-glucosamine and l-sorbose. Like the mutants previously selected for resistance to 2-deoxy-d-glucose, the new mutants described are all shown to be alleles of the ftr cistron.
General and specific effects of modifiers of mutant expression
Authors: Thompson James N.
Published: September 2009

Strains homozygous for mutants affecting the length of the L4 vein in Drosophila melanogaster were selected for increased or decreased vein length. Substitution of chromosomes selected for their effect on one mutant into the genome of a non-homologous mutant has shown that many modifiers of mutant expression must be considered as acting generally on the character rather than affecting only a specific mutant.
Polarity of gene conversion and post-meiotic segregation at thebufflocus inSordaria brevicollis
Authors: Bond D. J.
Published: September 2009

The flanking markers of wild-type recombinant spores originating from crosses of spore colour mutants inSordaria brevicolliswere analysed. Recombinant asci were of two main types – either with one or with two wild-type spores. In most crosses the behaviour of flanking markers was significantly different for these two types of recombinant asci. The main differences were in the polarity of gene conversion (as inferred from parental outside marker combinations) and in the frequency of recombinant outside markers. These differences were interpreted in terms of hybrid DNA models of recombination and correction of heteroduplex DNA.
Genetic evidence for a polycistronic unit of transcription in the complex locus ‘14’ inPodospora anserinaII. Genetic analysis of informational suppressors
Authors: Picard Marguerite
Published: September 2009

Forty-one suppressors obtained after NG and EMS mutagenesis of two ‘polar’ mutants of segment ‘29’ inPodospora anserinawere genetically analysed. Three classes of suppressor could be distinguished on spectrum pattern criteria. One representative suppressor of each class was demonstrated to be non-gene specific. The class I suppressor was dominant and only suppressed polar mutants in segment ‘29’ and non-ICR-induced ones in genes where polarity cannot be determined. Class II and III suppressors were partially dominant and they suppressed polar, non-polar and even ICR-induced mutants. The difference between classes II and III seems to be only quantitative. According to whether class II and III suppressors are considered strongly or weakly allele-specific, two hypotheses are considered. First,tRNAs could be involved in all three classes of suppression: class I would be nonsense-specific and classes II and III would be nonsense-missense suppressors. Secondly,tRNA could be involved only in class I suppression, while ribosomal ambiguity could be responsible for class II and III suppression.
Developmental mutants in a homothallic strain ofPhysarum polycephalum
Authors: Wheals A. E.
Published: September 2009

A derivative line of the homothallic Colonia strain ofPhysarum polycephalumhas been isolated which produces plasmodia with high efficiency within clones of amoebae. Using the synergistic effect of ultraviolet light and caffeine, mutants of this line have been isolated which fail to undergo the developmental transition between haploid amoebae and diploid plasmodia (aptmutants). They are isolated by selecting for amoebae which fail to produce plasmodia within clones. Complementation tests of four mutants have shown that they are mutants of four different loci and they are recessive to wild-type. A further analysis of one mutant reveals that theapt-1locus is unlinked to three other known markers. Crosses of this mutant with heterothallic strains yield progeny which are homothallic indicating that the lesion is not a revertant from a homothallic to a heterothallic mating-type. The use of this system in isolating developmental mutants is discussed.