bluuebunny/crossref_metadata_2025 huggingface dataset:
Maintenance of kappa particles in cells recently deprived of gene K (stock 51, syngen 4) of Paramecium aurelia
Authors: Yeung K. K.
Published: September 2009

1. Heterozygous (K/k) killer paramecia containing kappa particles from stock 51, syngen 4 of Paramecium aurelia were passed through autogamy, and the kk offspring tested for killing ability and for presence of stainable kappa particles at various fission stages.

2. After eight fissions, a small proportion of the paramecia were non-killers, and a few lacked stainable particles. After the 12th fission nearly all cells lacked kappa.

3. Mild starvation of the kk kappa-bearing paramecia resulted in complete loss of kappa and conversion to non-killers, even when applied to animals only one fission after the loss of gene K at autogamy.

4. The results obtained here show some discrepancy with data obtained earlier, both with kappa, and with mu particles in stock 540, syngen 1. The reasons for this discrepancy are at present not clear.
Mutagen specificity among reversions of ultraviolet-inducedadenine-1mutants ofSchizosaccharomyces pombe
Authors: Clarke C. H.
Published: September 2009

Ten U.V.-induced mutants at theadenine-1 locus ofSchizosaccharomyces pombediffer not only in their intragenic location but also in their spontaneous, HNO2- and U.V.-induced frequencies of reversion to adenine-independence. Seven mutants reverted with HNO2and of these only two reverted also with U.V.; the other three did not revert with either HNO2or U.V.

Genetic analysis of revertants showed that they could be due to suppressor mutations at a locus or loci far from theadenine-1locus, or to events extremely close to, if not identical with, the original site of mutation. Many distant suppressors were found among spontaneous revertants of someadenine-1andadenine-7allles, but such suppressors appear to be less frequent among the fiveadenine-8mutants tested. There are large differences between different sites at the same locus in the proportion of their spontaneous revertants due to distant suppressor mutations. Nitrous acid-induced revertants ofadenine1-,adenine-7, andadenine-8mutants were almost all of a type containing no detectable suppressor mutation. In the three cases studied, U.V.-induced revertants could be either predominantly of a suppressor or non-suppressor type, depending on the particular mutant examined.

Striking examples of mutagen specificity were found in which a particular mutant gave mostly suppressor-type revertants with one mutagen, while with another mutagen revertants were mainly of a type containing no detectable suppressor mutation.
Mutation rates at a new set of specific loci in the mouse
Authors: Lyon Mary F. , Morris T.
Published: September 2009

Previous measurements of specific locus mutation rates in mice had all involved the seven loci,a, b, c, d, p, sandse. An experiment was performed with the same mouse stock (C3H × 101) and the same radiation dose (600 rad) to spermatogonia as had been used previously, but employing a new group of six loci,a, bp, fz, In, paandpe. The observed mutation rate, 5·0 × 10−8per locus per rad, was significantly lower than that for the original seven loci, but was three to four times higher than the corresponding mutation rate inDrosophila melanogaster.
The nature and incidence of conjugation factors inEscherichia coli
Authors: Meynell Elinor , Datta Naomi
Published: September 2009

The sex factor F is itself exceptional among conjugation factors in being freely expressed in all the bacteria of a culture, while related factors which are largely unexpressed are widespread. These can be recognized by the presence of a small proportion of cells sensitive to phage specific for F+bacteria, and may sometimes constitute the conjugation factors associated with colicinogeny. Moreover, F itself can mutate to the repressed state so that derivatives ofE. coliK12 which appear F−include some in which F is still present but rarely expressed.
Genetic divergence in M. Vetukhiv's experimental populations ofDrosophila pseudoobscura3. Divergence in Body Size
Authors: Anderson Wyatt W.
Published: September 2009

1. Six initially identical populations ofDrosophila pseudoobscurahave been maintained in population cages for 7 years. Two populations have been kept at 16°C, two at 25°C, and two at 27°C.

2. One and a half years after the start, there was no significant genetic divergence in body size among the populations. When the populations were about 6 years old, a striking genetic divergence in body size was found. The genetic difference between the populations having the smallest and the largest mean sizes is over half the total phenotypic change in size between the two extreme temperatures at which the populations were kept. The populations kept at the lower temperature have genetically larger flies than the populations kept at the higher temperatures.

3. Accompanying the changes in body size were changes in the time of develop ment from egg to adult, the faster developers being the larger flies.

4. The F1hybrids from crossses between Vetukhiv's populations showed non-additivity of the genes for body size, the F1's in most cases being significantly larger than the midparent. There was no change in variability of body size in the F1or F2hybrids.

5. The temperature-directed selection for body size found in Vetukhiv's experimental populations may well be similar in kind to that which has produced temperature-oriented geographic gradients for body size in natural populations of several species ofDrosophila.
Selection for developmental canalisation
Authors: Waddington C. H. , Robertson E.
Published: September 2009

Starting from a genetically variable stock homo- or hemi-zygous for Bar two selection lines were set up, one selected for decreased sensitivity to the effect of larval temperature on eye size (‘canalization line’), the other for increased sensitivity (‘anti-canalization line’). In each generation a sample of larvae was grown at 25°C. throughout life and another sample at 25°C. for the first 48 hours, followed by 18°C. until emergence. In the canalization lines a selection was made of individuals (five males and five females out of 100) least affected by the temperature treatment and the anti-canalization line for a similar number most affected by the treatment. These ten males and females were allowed to mate at random and from the eggs produced random samples were then treated in the next generation in a similar manner in the two temperatures. Precise counts of facet numbers on the right eyes were made at generations 4 and 9 and it was clear that selection had been effective both in decreasing and increasing temperature sensitivity.

The whole canalization line can be regarded as a population which has been subjected to disruptive selection for two different criteria: one (small eyes) being regarded as adaptive to the low-temperature regine or habitat; the other (large eyes) being regarded as adaptive to the high-temperature habitat. A similar type of analysis can be applied to the anti-canalization line in which, however, the selective values of the phenotype are regarded as reversed in value in the two habitats. The experimental procedure employed involved not only random mating between individuals selected according to these two criteria but also random allocation of the offspring of this panmictic population to the two habitats of the next generation. This corresponds to a natural population in which there is disruptive selection exerted by two different habitats but no habitat preferences exhibited by members of the population. Under these circumstances, in our experiments, disruptive selection produced only rather slight increases in phenotypic variance, which were rather larger in the anti-canalization than in the canalization lines. Possible reasons for the difference between this result and those reported by Thoday and Gibson are discussed, and it is suggested that an important reason may be the slowness of the response to selection in the first few generations in our lines.
A super-suppressor on the thirteenth linkage group inSaccharomyces
Authors: Oshima Yasuji , Oshima Ikue
Published: September 2009

It has been proved that the suppression of seven different auxotrophic mutant alleles is brought about by a single super-suppressor allele designatedS.Super-suppressorSis allele-specific rather than locus-specific and is dominant to its wild-type allele.

Suppressible mutant alleles show no linkage relationships either among themselves or with the suppressorS.

Super-suppressorShas been shown to be closely linked (about 5 stranes) to one of the centromeres other than those of linkage groups I to XII. This establishes a new thirteenth linkage group.

The possible mechanism of action of the super-suppressor is discussed.
Compatibility and stability of diploids inCoprinus lagopus
Authors: Casselton Lorna A. , Lewis D.
Published: September 2009

Artificially selected diploids ofCoprinus lagopuswhen mated in compatible combinations, either together or with haploids, produce dikaryotic mycelia which are typical of normal haploid-haploid dikaryons. In a diploid-haploid dikaryon, the diploid nucleus is not as stable as when alone in a monokaryon but it can persist through repeated sub-culturing into a fruiting body and eventually through meiosis into the basidiospores. In a diploid–diploid dikaryon either one or the other nucleus becomes haploid so that fruiting bodies with two diploid nuclei are never formed. This fact constitutes a restriction on diploidy in nature and a useful method of reducing diploids to the haploid state.

Matings that might be considered to be incompatible at theBmating gene show a significant difference which is related to the number ofBalleles common to the mating colonies. Matings with oneBallele in common, e.g.B3B6+B2B3produce fully compatible and normal dikaryons. Matings with twoBalleles in common, e.g.B3B6+B3B6have, at first while the diploid nuclei still persist, the appearance of an incompatible commonBhaploid heterokaryon. This indicates that theBincompatibility system is based not on a complementary action between differentBalleles but on an oppositional action between the same alleles neutralizing theBgene product which is necessary for dikaryon formation.
F-prime factor formation inE. coliK12
Authors: Scaife John
Published: September 2009

A model for F-prime formation is presented. It predicts that an Hfr strain giving rise to an F-prime factor would acquire a deletion corresponding to the chromosomal fragment carried by the episome. Genetic studies have confirmed this prediction. Concomitant transfer to the episome of a gene determining a function vital to the cell has permitted selection of derived Hfr strains in which the episomal fragment has been translocated to various sites on the bacterial chromosome.
Ovulation and post-ovulational losses in strains of mice selected from large and small litters
Authors: Bateman Nigel
Published: September 2009

This paper describes the aspects of fertility that had been affected by selection on litter size. For twelve generations previously the mice used as parents were chosen because they had been born in large or small litters. At the end of this time, litters in the fertile strain averaged 11·1 young born alive, while the less fertile strain averaged 5·5.

It was found that male fertility and inherent viability of the young had nothing to do with the response although neither was excluded by the method of selection. Several contributions, however, were made by the females, who were affected not only in ovulation rate, but also in their control of pre-implantational losses, foetal mortality and mortality of the newly born.

Females from the less fertile strain were particularly prone to pre-implantational loss of eggs. It remains to be shown whether these were due to fertilizational or implantational failure.

The incidence of earlier and later embroyonic losses in females of the same strain were uncorrelated—Utters that were depleted early were neither more nor less inclined to be depleted later.
Purification of argininosuccinase fromNeurosporaand comparison of some properties of the wild-type enzyme and an enzyme formed by inter-allelic complementation
Authors: Cohen Brian B. , Bishop John O.
Published: September 2009

Argininosuccinase has been purified from wild-typeNeurospora crassa, strain ST.A. The purified enzyme, which is homogeneous by the criteria of analytical centrifugation and starch-gel electrophoresis, has a molecular weight of about 175,000. The enzyme has also been partially purified from a heterokaryon between thearg-10 mutant stocks B317–9–9aand 402–3a.

The reaction kinetics of the two enzymes were compared in several respects, and they were found to be indistinguishable. The enzymes were also indistinguishable by starch-gel electrophoresis, and sedimented at the same rate through a sucrose gradient. It seems likely, however, that the enzymes do differ physically since they showed different affinities for both calcium phosphate gel and hydroxylapatite during purification.
Effective population size when fertility is inherited
Authors: Nei Masatoshi , Murata Motoi
Published: September 2009

A formula for effective population size when fertility is inherited is worked out. It is shown that the effective size decreases as the heritability of fertility or progeny number increases.
Snell's waltzer, a new mutation affecting behaviour and the inner ear in the mouse
Authors: Deol M. S. , Green Margaret C.
Published: September 2009

A new recessive gene affecting behaviour and the inner ear in the mouse has been discovered. It was named Snell's waltzer, and assigned the symbol sv. It is in linkage group II, about two map units from short ear (se) on the side opposite to that of luxoid (lu). The behaviour of sv/sv mice closely resembles that of other members of the shaker-waltzer group. The abnormalities of the inner ear consist in degeneration of certain parts following normal morphogenesis. The entire neuro-epithelium —that is, the organ of Corti, the two maculae and the three cristae—is affected, and this feature distinguishes it from other degenerative type mutants of this group.
Recombination within theamgene ofNeurospora crassa
Authors: Fincham J. R. S. , Pateman J. A.
Published: September 2009

Maps have been made showing the order ofammutant sites using (a) frequencies ofam+recombinants from crosses betweenammutants and (b) the modes of distribution of theam+recombinants among the two parental and two recombinant classes with respect to the flanking markersinosandsp.

It is possible to arrange the sites in an order such that, in almost all the crosses yielding useful numbers ofam+recombinants, thespallele originally in coupling with the distalammutant site occurs in the majority of the recombinants. No such consistent pattern was found with respect to theinosmarker. The order obtained by reference tospagreed with the best order deducible from recombination frequencies.

The data are consistent with the hypothesis thatam+recombinants arise by a process of gene conversion, that there is a gradient of conversion frequencies from the right (inosor distal) end of the gene to the left (spor proximal) end, and that conversion tends to be associated (though less than 50% of the time) with crossing-over, especially on the distal side.

There is no obvious relationship between the map position of a givenammutant and the properties of the protein product of the mutant gene.
Dilution of gene products in the cytoplasm of heterokaryons inCoprinus lagopus
Authors: Casselton Lorna A. , Lewis D.
Published: September 2009

(a)Coprinus lagopushas in nature both a monokaryon with one haploid nucleus per cell and a dikaryon with two haploid nuclei per cell. It also has in experiment both a heterokaryon with two types of nuclei distributed irregularly in the mycelium and a diploid monokaryon with one diploid nucleus per cell.

(b) Two pairs of linked recessive auxotrophic mutants,me-5ad-8 andadhis-1chol-1 have been combined in two different sets of multiple heterogenotes so that in the dikaryon and heterokaryon the + (active) alleles of the four genes are distributed equally in the two component nuclei. In one combination the linked genes are intransand in the other they are incisarrangement in diploid, dikaryon and heterokaryon.

(c) Complementation between the + genes, as measured by growth on minimal and complete media, was complete in the diploid and dikaryon but was only partial in the heterokaryon.

(d) A similar comparison of a recessive suppressor of the mutantme-1 revealed that the recessive gene was not expressed and therefore was fully recessive in the diploid and dikaryon but was only partially recessive in the heterokaryon.

(e) The exact similarity of complementation of the structural genes of the auxotrophic mutants and the recessiveness of theme-1 suppressor in diploids and dikaryons exclude a localization of gene interaction in the nucleus. In a heterokaryon cytoplasmic dilution of the product of a dominant gene can occur and has the effect of producing a phenotypic difference between heterokaryons and diploids.
Mutants of bacteriophage lambda able to grow on the restricting hostEscherichia colistrain W
Authors: Glover S. W. , Aronovitch J.
Published: September 2009

Escherichia colistrain W adsorbs phage λ very efficiently but the phage does not form plaques on this strain because the DNA of λ is broken down in a majority of the infected cells shortly after adsorption. In a 10−3to 10−4fraction of the infected cells λ grows and small bursts of phage are produced. This phage does not carry the W-specific host modification and is unable to complete a second round of infection in W (Kerszman, Glover & Aronovitch, 1967). λω mutants have been isolated which are able to escape this restriction process and which plate on W with an efficiency of 1·0 and when grown in W these mutants carry a W-specific host modification.
Genetic control of recombination and the incompatibility system inSchizophyllum commune
Authors: Simchen G.
Published: September 2009

Crossing-over between the α and the β loci constituting theAincompatibility factor gives rise to two new specificities which are compatible with both parental As and with each other. The frequency of monokaryotic mycelia carrying re-combinant A factors is shown to be under genotypic control in a multiple crosses programme (6 × 6), selection for high and low recombination frequencies (two generations), and crosses between the selection lines. The recombination values based on samples of 100 monokaryons, range from 0 to 21%; however, the more accurately estimated values of the ‘High’ and ‘Low’ selections are 14% and 4%, each being based on approximately 2,000 mycelia.

The data are compatible with a gene-system consisting of the postulated locusrecwhich has a major effect on recombination and which is linked to the A factor, and several minor effects by other loci. Alternative interpretations are presented and discussed. The apparent dominance of low frequencies of recombination on high frequencies can be related to the breeding behaviour ofS. commune.Thus close linkage between α and β allows a high number of A specificities to be maintained in a population as well as high out-breeding potential, while the inbreeding potential (i.e. dikaryotic combinations between monokaryons originating from a single fruit-body) is kept low and near its minimum.

The significance of the two-locus structure of the incompatibility factors is examined theoretically in an Appendix at the end of the Discussion section.
Sex differences in recombination of linked genes in animals
Authors: Dunn L. C. , Bennett Dorothea
Published: September 2009

Reports of sex differences in crossing-over in animals, published since Haldane in 1922 suggested that crossing-over should be less frequent in the heterogametic sex, have been reviewed and discussed. No general rule is discernible apart from the absence of crossing-over in males of the dipteran generaDrosophilaandPhryneand in females of some lepidopteran species, due apparently to failure of chiasma formation in the heterogametic sex. In the majority of animal species examined crossing-over occurs in both sexes. While there is some tendency in mammals for crossover values in females to exceed those in males, it was of greater interest to find that marked sex-differences occur in the same species (data chiefly from the house mouse) in opposite directions in different chromosomes. The influence of factors acting locally in the chromosomes, such as those associated with hetero-chromatin, were indicated as promising subjects for the study of variations associated with sex.
Inhibition of respiratory enzyme synthesis in yeast by chloramphenicol: Relationship between chloramphenicol tolerance and resistance to other antibacterial antibiotics
Authors: Wilkie D. , Saunders G. , Linnane Anthony W.
Published: September 2009

Individual yeast strains show characteristic differences in the amount of chloramphenicol required to inhibit the synthesis of the respiratory system. This varies from 0·05 mg./ml. to 4 mg./ml. A correlation between chloramphenicol and tetracycline resistance appears likely but no correlation between chloramphenicol and erythromycin resistance was observed. These relationships were emphasized by cross-checking spontaneous resistant mutants for each antibiotic. Nearly all mutants showing spontaneous resistance to chloramphenicol had a simultaneous increase in tetracycline resistance but no increase in erythromycin resistance. Spontaneous resistance to erythromycin on the other hand, had no striking effect on tolerance levels to chloramphenicol and tetracycline. Increases in erythromycin resistance were commonly accompanied by an increase in resistance to other macrolide antibiotics. There are similarities between these effects and those described for certain bacterial systems.
Chromosomal location of a mutation causing chloramphenicol resistance inEscherichia coliK 12
Authors: Reeve E. C. R. , Suttie D. R.
Published: September 2009

A chloramphenicol-resistant mutation inEscherichia coliK 12,cmlA1(previously designated1a), giving a higher Cm-resistance than other mutations yet examined, has been shown to have a chromosomal location, the gene order beinggal, λ,bio,cmlA,pyrD. CmlAcan be transduced efficiently into cm-sensitive strains by P1 with little phenotypic lag, and is co-transduced with the λ-attachment site (frequency 1·13%) but not withgalorpyrD.
The extent ofrIIdeletions in phage T4
Authors: Dove William F.
Published: September 2009

The extent of certainrIIdeletions in phage T4 has been mapped by genetic means beyond the terminus of the B cistron. They extend to varying degrees, nearly to theacslocus. The phenotypes of these mutants indicate that there are two or three cistrons betweenrIIB andacs, and that the functions coded for by these cistrons are not essential for growth in any knownE. coliK12 strain orE. colilysogen.
Chromosome pairing in altered constitutions and models of synapsis and crossing-over
Authors: Maguire Marjorie P.
Published: September 2009

Metaphase trivalent frequencies from a number of new chromosomal constitutions (various combinations of maize chromosome 2-Tripsacumhomeologue primary and secondary interchanges) are presented and compared to previous findings from similar material. It is suggested than an underlying direct relationship may exist between extent of gentic map present in duplicate and triplicate and expectation from a sharing of map probability of crossing-over among all homologues. Theoretical considerations are discussed.
Tests for an effect of the Y-chromosome on the mutagenic action of formaldehyde and X-rays in Drosophila melanogaster
Authors: Ratnayake Winston E.
Published: September 2009

An additional Y-chromosome in either male or female did not have an influence on the mutagenic action of formaldehyde–food. It is concluded that the lack of response of female germs cells to this treatment is not due to lack of a Y-chromosome, and that the specific response of spermatocytes among germ cells is probably not due to the striking activity of the Y in these cells.

Kershner's (1949) observation that the sex-linked lethal frequency in X-rayed males was significantly reduced by an additional Y-chromosome could not be confirmed.
Chimerism and genetic mapping
Authors: Stewart John S. S.
Published: September 2009

Different types of chimerism result from double fertilization. Differences result from fertilization of first and second polar bodies and from early fusion of two zygotes. These three types of chimerism have different phenotypes or different proportions of possible phenotypes, and variation is greater in respect of gene loci close to the centromere. The phenotype frequencies in the different types of chimerism are tabulated and the phenotype frequencies expected in different mating types are shown. Studies of such cases offer the only method of autosomal gene localization relative to the centromere at present available in man.
Modification by an R determinant for streptomycin of hissd phenotype in a mutant strain of Escherichia coli B
Authors: Molina A. M. , Calegari L. , Conte G.
Published: September 2009

When an R determinant for streptomycin is transferred into a conditionally streptomycin-dependent E. coli B mutant—which requires in minimal medium either histidine or streptomycin—the latter behaves like a histidineless strain. This phenotype modification shows that the repairing action of streptomycin is prevented. The specific requirement of the strain is not now replaced even by streptomycin concentrations up to 10000 µg/ml at which the conditionally streptomycin-dependent mutant could originally grow, and which are well beyond the resistance level characteristic of the R determinant itself. These data seem to suggest that a reduction in permeability of the cell membrane cannot be held responsible for the phenomenon observed.
Investigation of the mating system ofPseudomonas aeruginosastrain 1: III. Kinetic studies on the transfer of the sex factor (FP)
Authors: Loutit J. S. , Marinus M. G. , Pearce L. E.
Published: September 2009

FP transfer to recombinant and non-recombinant recipients ofPseudomonas aeruginosastrain I has been investigated under controlled conditions. When transferred to recombinants, the sex factor appeared to enter first and did not seem to be linked to the early chromosome markers. Five to twenty percent of the recipient population were found to be FP+, depending on the time allowed for pairing. Only 40% of the recombinants were FP+at 90 min. A possible relationship between FP and chromosome has been discussed.
The incorporation of alien disease resistance in wheat by genetic interference with the regulation of meiotic chromosome synapsis
Authors: Riley Ralph , Chapman Victor , Johnson Roy
Published: September 2009

1. Triticum aestivum ssp. vulgare variety Chinese Spring (2n = 6x = 42) is susceptible to yellow rust caused by Puccinia striiformis while the wild annual grass Aegilops comosa (2n = 14) is resistant to all the physiologic races for which it has been tested.

2. By a backcrossing programme initiated from Chinese Spring × Ae. comosa hybrids, using Chinese Spring as the recurrent parent, a line was isolated with a single chromosome of Ae. comosa, determining rust resistance, added to the full complement of Chinese Spring.

3. The alien chromosome substituted with good genetic compensation only for the chromosomes of homoeologous group 2 of Chinese Spring. This demonstrated that the chromosome determining rust resistance is in homoeologous group 2. It was designated 2M since Ae. comosa has the M genome.

4. In order to induce recombination between 2M and its wheat homoeologues, hybrids were made using Ae. speltoides which has the capacity to suppress the activity of chromosome 5B that normally prevents homoeologous synapsis. A backcrossing programme, using Chinese Spring as the recurrent parent, was reinitiated from the 29-chromosome hybrids carrying chromosome 2M and the haploid complements of Chinese Spring and Ae. speltoides.

5. Selection was practised for rust resistance and ultimately a resistant plant with 42 chromosomes, that formed 21 bivalents at meiosis, was isolated. This plant was heterozygous for a dominant rust resistance allele (Yr8) derived from Ae. comosa. Homozygotes were isolated in its progeny and in this way the rust resistant breeder's variety, Compair, was established.

6. Compair differs from Chinese Spring in its yellow rust resistance which was shown to be determined by a chromosome corresponding to 2D of Chinese Spring. This chromosome of Compair has the short arm, the centromere and a proximal segment of the long arm of chromosome 2M and a distal segment of the right arm of chromosome 2D. The modified chromosome, which is designated 2M/D, arose by homoeologous recombination in the Ae. speltoides hybrid or in the immediately succeeding backcross generations. Chromosome 2M/D carries the Yr8 gene in the proximal segment of the long arm derived from chromosome 2M.

7. In hybrids between Compair and standard wheat varieties, chromosome 2M/D pairs regularly with chromosome 2D so that regular segregation of Yr8 can be expected and Compair treated like any other parental variety in wheat hybridization programmes.

8. This work illustrates the way that homoeologous recombination can be induced and exploited both in cytogenetic analysis in wheat and in practical breeding work. The nature of the meiotic synapsis of chromosome 2M/D with its partial homologues raises questions concerning the means by which chromosome 5B influences the specificity of meiotic synapsis.
Environmental influences on puffing in the salivary gland chromosomes ofDrosophila melanogaster
Authors: Burnet Barrie , Hartmann-Goldstein Ingeborg
Published: September 2009

The sequence of development of salivary gland chromosome puffs inDrosophila melanogastercultured on live yeast and RNA-deficient medium has been studied in late larval and prepupal stages. Differences in puffing pattern between individuals cultured in the two environments are almost entirely due to shifts in the relative timing of puff development at specific chromosome sites. Detailed studies on the right arm of the second chromosome indicate that, at certain sites, puffing activity spreads to adjacent lettered subdivisions of the chromosome. There are differences in the extent of lateral spreading of activity into adjacent regions in the two environments which may be due to clustering of functionally related genes.
Duration of meiosis in barley
Authors: Bennett M. D. , Finch R. A.
Published: September 2009

The duration of meiosis and its stages has been estimated in Hordeum vulgare variety Sultan grown at 20·0 °C with continuous illumination. The results are in good agreement with a previous estimate of the duration of meiosis and some of its stages in barley. The duration in barley does not differ greatly from that predicted from the previously calculated regression of DNA amount on meiotic duration in diploid plant species. As in other cereal species, meiosis is comparatively short.
Improvement of litter size in a strain of mice at a selection limit
Authors: Falconer D. S.
Published: September 2009

A strain of mice that had ceased to respond to selection for high litter size was inbred with continued selection. Depression of the mean proved the existence of residual genetic variance. Four lines survived the inbreeding, and one reached 20 generations with a mean equal to the original strain, thus disproving overdominance as a major cause of the residual variation. The four selected inbred lines were crossed and a new strain derived from the cross was maintained in parallel with the original strain. The new strain showed an improvement of 1·5 mice per litter over the original strain. Thus selection with inbreeding was able to achieve an advance beyond the limit attained by the original selection.

The hypothesis that the residual variation was due to genes with simple dominance was tested by seeing if it could account for the observations with reasonable values of the relevant parameters. The improvement made by the inbreeding and crossing required the elimination of about 30 recessive genes with effects (homozygote difference) of 0·5 phenotypic standard deviations and gene frequencies of 0·2. Consideration of the mean levels of the selected inbred lines in conjunction with the rate of depression found on inbreeding without selection showed that the selection with inbreeding had eliminated about 75% of the segregating reces-sives. The number of genes contributing to the residual variance was therefore about 40. The additive variance generated by these genes was just consistent with the estimate of zero from the realized heritability. Consideration of the original selection showed that about half the genes could have been still segregating when the response ceased. The hypothesis therefore requires the number of genes in the base population to have been about 80. The number of genes required, though large, does not seem impossible, and the hypothesis of genes with simple dominance can account for all the observations.
A semi-automatic technique for conducting many bacterial matings concurrently
Authors: Achtman Mark
Published: September 2009

A technique using microserological equipment is described whereby up to 144 quantitative interrupted bacterial matings may be performed concurrently. The technique is easy to use, accurate and reproducible, and eliminates the need for agar plates. However, it is only suitable for 40–42 °C matings and mating efficiency is approximately threefold lower than in test tubes.
Mutants ofAspergillus nidulansunable to use choline-0-sulphate
Authors: Arst Herbert N.
Published: September 2009

Mutants ofAspergillus nidulansunable to use either the choline moiety or the sulphate moiety of exogenous choline-0-sulphate have been selected. Choline-0-sulphate non-utilizing (csu) mutations have no other apparent pleiotropic effects, but it has not yet been established whether they lead to loss of choline sulphatase (and thus of the ability to utilize endogenously produced choline-0-sulphate) or to loss of a specific transport system for choline-0-sulphate or to loss of both.
Transduction mechanisms of bacteriophage ε15III. A new class of mutations affecting the conversion ofSalmonella anatumby bacteriophage ε15
Authors: Hedges R. W.
Published: September 2009

Salmonella anatumlysogenized by a doubly mutant strain of bacteriophage εγshows a markedly rough colonial phenotype on tetrazolium agar. Mutants that abolish the roughness are reported.
An invariant property of a structured population
Authors: Maruyama Takeo
Published: September 2009

Considering a single mutant gene in a geographically subdivided finite population, it is shown that the average number of heterozygotes, due to this gene, that appear in the population before fixation or loss of this gene is equal to twice the total population number. This is invariant under the geographical structure of the population.
Pattern of neutral polymorphism in a geographically structured population
Authors: Kimura Motoo , Maruyama Takeo
Published: September 2009

In a two-dimensional stepping-stone model of finite size, if a pair of alleles happen to segregate in the whole population, marked local differentiation of gene frequencies can occur only if migration between colonies is sufficiently rare so thatNm< 1, whereNis the effective size of each colony andmis the rate at which each colony exchanges individuals with four surrounding colonies each generation. On the other hand, ifNm≥ 4, the whole population behaves as if it were panmictic and the allelic frequencies become uniform over the entire distribution range unless mutation is unusually high. Tendency toward local differentiation is much weaker in two-dimensional than in one-dimensional habitats.
The time course of recombinant production inStreptomyces coelicolor
Authors: Sermonti G. , Puglia A. Maria , Ficarra Giuseppina
Published: September 2009

The process leading to gene recombination can be interrupted in the filamentous bacteriaStreptomyces coelicolorby growing mixed cultures on cellophane disks lying on complete medium. The mycelium is harvested, broken, diluted and the broken hyphae plated at different time intervals. By this means some markers can be excluded from heteroclones or from recombinant progeny in early samples. The recombinant pattern clearly changes with time, with an increase of markers contributed to the recombinant progeny. In crosses between male (NF) and female (UF) strains, the maleness is the first donor trait to appear in the cells of the recipient parent. The fertility factor does not produce a transfer origin on the donor chromosomes; the donor contribution may extend on either side or on both sides of the factor which appears to be compulsory for zygote formation. The longer the time of contact between parental cells, the longer the segment of the donor chromosome contributing to the recombinant progeny. When spores are formed they contain almost exclusively recombinant nuclei derived from segregation processes.
Mutants ofCoprinus lagopusselected for resistance to 2-deoxy-D-glucose
Authors: Moore David , Stewart George R.
Published: September 2009

The glucose analogue 2-deoxy-D-glucose seriously inhibits the growth ofCoprimts lagopus. Following treatment withN-methyl-N′-nitro-N-nitrosoguanidine 388 resistant mutants were isolated. It is shown that the mutants isolated are probably allelic; they were phenotypically similar and no complementation was observed. The mutants were pleiotropic in the sense that although they were initially selected only for resistance to 2-deoxy-D-glucose they were found to be cross-resistant to both of the related analogues, sorbose and glucosamine. Furthermore, the mutants were unable to utilize fructose as a sole carbon source. It is demonstrated that the inability to utilize fructose results from a defect in sugar transport. The gene symbolftris proposed for this cistron and it is shown that though the gene is quite closely linked to its own centromere, it is unlinked to centromere markers of the six known linkage groups.
Isolation and properties of mutants of the FP2 sex factor ofPseudomonas aeruginosa
Authors: Stanisich Vilma A.
Published: September 2009

Two new types of mutants of the FP2 sex factor have been isolated in males ofP. aeruginosastrain PAT. Males harbouring FPd mutants are unable to mediate either sex factor or host chromosome transfer, although they retain the exclusion and precipitation characteristics of wild-type males. Males harbouring the FPs mutant apparently have an altered cell surface as indicated by their loss of precipitability, and although their donor properties are similar to those of wild-type males they show a slightly reduced conjugal fertility.

A previously described sex factor mutant FP* (Stanisich & Holloway, 1972) can be transferred to males carrying either the FPs or FPd factors, and the heterozygous strains produced show restoration of wild-type properties, i.e. wild-type precipitation characteristics of the FPs mutants, and transferability of FPd mutants respectively. This suggests that the mutations of the FPs and FPd factors are recessive to the alleles carried by the FP* factor. The ability to produce such heterozygous strains supports the view that at least two copies of the FP2 factor occur in strain PAT males.
Genetic differences between populations ofDrosophila melanogasterfor a quantitative trait: I. Laboratory populations
Authors: López-Fanjul C. , Hill W. G.
Published: September 2009

An experiment was carried out to test whether two laboratory cage populations ofDrosophila melanogasterfrom different origins (Kaduna and Pacific) differed in the genes for sternopleural bristle number. The means, variances and heritabilities of the two populations and the synthetic formed from crosses between them were very similar.

Selection for low bristle number was practised in small replicate lines, six of each pure population and nine of the synthetic. On average, Pacific responded to selection rather more rapidly than either Kaduna or the synthetic, but there was little difference in the limit achieved.

Crosses between replicates within populations were made and selection continued, and these lines subsequently crossed between populations and reselected. Additional response was obtained by this procedure but the crosses between the replicates of the pure and synthetic populations attained similar selection limits.

An analysis of effects of individual chromosomes from the selected lines on bristle number indicated that the contribution of each chromosome to total response was about the same in Pacific, Kaduna and the synthetic.

It is concluded that differences in gene frequency, rather than the presence or absence of particular alleles, are mainly responsible for the differences observed between the populations.
Genetic recombination betweenKlebsiella pneumoniaeandEnterobacter aerogenes
Authors: Matsumoto Hideki
Published: September 2009

Intergeneric recombination of chromosomal genes between strains ofKlebsiella pneumoniaeandEnterobacter aerogeneshas been observed. In these experiments a male strain ofK. pneumoniaeacted as donor andE. aerogenesacted as recipient. Closely linked genes were co-transferred with very high frequency, and transfer of a large fragment carrying several separated genes was not uncommon. Subcultures of a hybrid which had received a large fragment carrying five markers were tested for genetic stability; no spontaneous segregants were found among 34000 colonies tested. These results suggest that the transferred fragment had been integrated, and indicate the close genetic relationship betweenK. pneumoniaeandE. aerogenes. This is in agreement with their very similar biochemical properties.
R-Factors used for genetic studies in strains ofPseudomonas aeruginosaand their origin
Authors: Holloway B. W. , Richmond M. H.
Published: September 2009

The origin of a number of R-factors used for genetic studies inPseudomonas aeruginosais described.
Natural selection with varying selection coefficients – a haploid model
Authors: Gillespie J. H.
Published: September 2009

In this paper an exact treatment is given for the stochastic behaviour of the frequency of haploid genotypes in an infinite population when the absolute fitnesses of the two genotypes vary at random over generations. The main qualitative result from this treatment is that natural selection will favour that allele with the largest geometric mean fitness. A diffusion equation is derived whose solution is identical to the exact solution. The drift coefficient for this equation is of the form − μp(1 −p) + σ2(½ −p)p(l −p). This differs from the drift coefficient used in previous treatments of this problem and reduces the rate of quasi-fixation. Various waiting time problems are solved using this diffusion equation.
Conditional mutations affecting the cell envelope ofEscherichia coliK-12
Authors: Egan A. F. , Russell R. R. B.
Published: September 2009

Amongst a collection of temperature sensitive (TS) mutants ofEscherichia coliK-12, some have been found which can grow at the restrictive temperature (42 °C) if the osmotic pressure of the medium is raised by the addition of sodium chloride (1%) or sucrose (12·5%). These mutants are described as temperature sensitive osmotic remedial (TSOR) mutants. At the restrictive temperature they are not osmotically fragile, but do display decreased resistance to inhibitory agents such as deoxycholate, actino-mycin D and acridine orange; they also show release of the periplasmic enzyme ribonuclease. These results indicate a change in the cell's outer permeability barrier. The genes affected in six of the mutants have been located on theE. colilinkage map. The mutations, which occur at loci not previously described, have been namedenvM–envTto indicate their effect on the cellenvelope.
Random selective advantages of genes and their probabilities of fixation
Authors: Jensen Louis
Published: September 2009

The question of what is meant by random fluctuations in selection intensities in a finite population is re-examined. The model presented describes the change in the frequency of a gene in a haploid population of sizeM. It is assumed that in any generation the adaptive values ofAandaare equally likely to be 1 +s: 1 or 1: 1 +s. Ifsis the selective advantage andxthe frequency of geneA, then the first two moments of the change in frequency are found to bem(Δx) =x(1 −x)(1 − 2x) θ/2Mand

whereE(s2) = θ/M. The ultimate probability of fixation is computed, showing that variability in selection increases the chance of fixation of a rare gene. A more general form form(Δx) also is obtained. This form is compared with the equation currently used in describing random fluctuations in selection intensities.
Genetic control of metabolism: enzyme studies of theobeseandadiposemutants in the mouse
Authors: Bulfield Grahame
Published: September 2009

The activity of several enzymes has been determined in the livers of homozygousobeseandadiposemice, their normal litter-mates, and phenocopies induced in normal mice by aurothioglucose (ATG) injections.

Obese, adiposeand ATG mice had higher activities of ATP citrate lyase, malic enzyme (NADP malate dehydrogenase) and pyruvate kinase than normal mice. Heterozygote activities are indistinguishable from wild-type. There was no difference between normal and fat litter-mates in the activity of malate dehydrogenase (NAD-linked), lactate dehydrogenase, isocitrate dehydrogenase and fumarase.

Crosses between mice doubly heterozygous for roth theadandobgenes produced offspring that were only ‘fat’ or ‘normal’ and no offspring could be phenotypically recognized as the double mutant, either physically or in terms of ATP citrate lyase activity.

Gas–liquid chromatography of the fatty acids of the depot fat showed no differences between any of the types of litter-mate.

The alterations found in enzyme activity inobeseandadiposemice are compared to several other enzyme activity differences reported in the literature forobesemice. These are discussed in relation to genetical criteria that may be estarlished to assess, from quantitative data, whether an enzyme is the site of the primary lesion in a mutant pheno-type. Some general observations are made on genetics and the control of metabolism.
Deoxyribonuclease-deficient mutants ofUstilago maydiswith altered recombination frequencies
Authors: Badman Rosemary
Published: September 2009

Current molecular models of genetic recombination invoke steps mediated by deoxyribonucleases. It is likely therefore that some mutants deficient in these enzymes would have defective recombination mechnisms. Mutants ofUstilago maydisdeficient in extracellular and intracellular DNase activity have been isolated. Three of the extracellular mutants are recessive and non-complementing, as are four of the intracellular mutants. The loci for extracellular and intracellular DNase deficiency have been namednuc-1andnuc-2respectively, and they are linked.

In crosses where each parent was deficient in both extracellular and intracellular DNase activity, meiotic allelic recombination (gene conversion) within thenarlocus was abolished, although crossing-over in one tested interval was apparently normal in frequency. In DNase-deficient diploids, no mitotic allelic recombination in thenarlocus was observed and the distribution of crossing over was abnormal. Nuclease deficiency did not appear to have any strong effect on radiation sensitivity.