bluuebunny/crossref_metadata_2025 huggingface dataset:
The genetics of fimbriation inEscherichia coli
Authors: Maccacaro G. A. , Hayes W.
Published: September 2009

(1) Fimbriated cells ofE. coli K-12 are of two types. In the Fim+type the expression of fimbriation is susceptible to reversible environmental suppression. This type gives rise to environment-stable mutants termed Fimσ+.

(2) Fimbriated cells can yield two types of non-fimbriated mutant, Fim−and Fimσ−, the latter arising from populations of Fimσ+cells. Neither type reverts to the fimbriated state.

(3) Both types of fimbriated and non-fimbriated cells can be distinguished by physiological and genetic criteria.

(4) Fimbriation of both types can be transferred to non-fimbriated cells of both types, and segregates among recombinants, in crosses mediated either by transduction or sexual conjugation.

(5) The genetic control of fimbriation involves at least two determinants, for one of which a chromosomal location (fim) has been mapped.

(6) Certain anomalies offimsegregation are interpreted in terms of negative interference over relatively large regions of the bacterial chromosome.
Genetic divergence in M. Vetukhiv's experimental populations ofDrosophila pseudoobscura1. Rudiments of sexual isolation
Authors: Ehrman Lee
Published: September 2009

Weak but statistically significant sexual isolation has been demonstrated among Vetukhiv's six experimental populations ofDrosophila pseudoobscura, all originally descended from founders taken from cultures of the same hybrids from four geographic localities. These six populations were maintained separately for almost 4½ years and then tested for the existence of sexual isolation. The sexual isolation has arisen in the absence of any selection for isolation, evidently as a by-product of genetic divergence.
The quantitative relations between variation in red eye pigment and related pteridine compounds inDrosophila melanogaster
Authors: Barthelmess Ilse B. , Robertson Forbes W.
Published: September 2009

The relations between the quantity of red eye pigment and related pteridine compounds ofDrosophila melanogasterhave been studied in a variety of genotypes, which include strains selected for high or low pigment content, various derivatives of these lines and also lines in which one or other of the major autosome pairs were represented by homozygous chromosome pairs, derived by random sampling from the base population and also inbred lines. The quantity of red pigment was defined by the optical density when whole heads were extracted in a suitable solvent, while the pteridines were separated by chromatography and their amounts estimated by means of their characteristic fluorescence.

The evidence from selection, inbreeding and chromosome sampling from the base population demonstrated the presence of substantial genetic variation for pigment content and amounts of related pteridines.

The genetic and biochemical properties of the selected lines differed according to the direction of selection. High lines remained heterozygous after many generations of selection and displayed dominance and epistasis in favour of higher pigment content in crosses to the unselected stock. Selection for low pigment content led to fixation of recessive effects, attributable to particular chromosomes. The dominance-recessive relationship in red pigment differences was also applicable to the associated pteridines.

The metabolic pattern in all lines with reduced pigment content is compatible with the assumption of reduced enzyme activity at particular steps of the pathway leading to the drosopterins (red eye pigments). The two steps accessible to study are subject to genetic variation in the base population, while inbreeding or selection for low pigment content leads to genetically fixed alterations at one or other of these steps. The genetic analysis was consistent with the biochemical evidence.

Increase in pigment content above the normal level, either by selection or chance fixation, is accompanied by correlated increase in all the precursors. Several alternatives are possible but it is suggested that this may be due to an increase in early precursors, before the stages which have been altered in the low pigment lines.

Attention is drawn to the similarity in genetic behaviour between pigment content and body size. Particular emphasis is laid on the value of selection as a means of creating biochemical differences which offer a basis for relating biochemical function and genetic behaviour.
Recombination events that span sites within neighbouring gene loci ofNeurospora
Authors: Murray Noreen E.
Published: September 2009

Evidence is given thatme-7andme-9are separate but contiguous gene loci.

The pattern of polarized recombination throughout theme-7 me-9region indicates the location of a recombinational discontinuity between the knownme-7alleles and the knownme-9alleles.

Recombination events may include sites in both genes but such events are not preferentially associated with parental combinations of flanking markers.

Recombination events extending into both genes provide an extra criterion for the ordering of the sites within theme-7locus. The order so obtained confirms that deduced from the flanking markers of me+recombinants fromme-7×me-7crosses.

Inme-7×me-9crosses butnotinme-7×me-7crosses, the map order derived on the assumption that single exchanges are more frequent than apparent triple exchanges is the reverse of that derived from prototroph frequencies. It is concluded that the former criterion is more likely to have provided the correct order and the anomalous prototroph frequencies reflect the polarity of gene conversion withinme-7.
On the fixation probability of mutant genes in a subdivided population
Authors: Maruyama Takeo
Published: September 2009

Following Moran's (1962) method, it was shown that the fixation probability of a mutant gene is not altered by the subdivision of a population into partially isolated colonies, if the following conditions are met; fitness is additive, samplings and selection is done separately in each colony, and migration between colonies does not change the gene frequency in the whole population. This conclusion was checked by simulation experiments.
The bearing of mutant and cross specificity on the pattern of intragenic recombination
Authors: Paszewski A. , Prazmo W.
Published: September 2009

Four white-spored allelic mutants ofAscobolus immersuswere used to study the effect of mutant and cross specificity on the recombination pattern in intragenic crosses.

In the locus studied no correlation was found between the position of mutants on the map and their basic conversion frequencies. One of the mutants evidently caused an increase of conversion frequency of the two others. Crossing-over in intragenic recombination may be mutant-specific as revealed by using two mutants which give no recombinants when crossed with each other. The frequency of crossing-over was higher in crosses in repulsion than in coupling involving the same pairs of mutants. Polarization observed in two-point crosses was due in some instances predominantly to differences in basic conversion frequencies of the mutants used, and in others to the relative position of the mutated sites. Mutants located in the central part of the studied region were those which converted most frequently in two-point crosses. No reciprocal conversions were observed.

A number of recombinant asci resulting from two or more separate but highly correlated recombinational events within a gene were found.
Survival, DNA-breakdown and induction of prophage lambda in aEscherichia coliK12recAuvrBdouble mutant
Authors: Hertman I. M.
Published: September 2009

Cellular functions of a double mutant ofEscherichia coliK 12 deficient in recombination (recA) and defective in excision of pyrimidine dimers (uvrB) have been compared to those of isogenicrecAoruvrBsingle mutants and ‘wild type’ bacteria. A combined effect of the two mutations on cell survival both under normal conditions of growth and after exposure to ultraviolet light or mitomycin C was demonstrated. The ratio of optical density to the number of colony formers in growing cultures of the double mutant is three times greater than in similar cultures of therecAsingle mutant and 9 times greater than in eitheruvrBor in ‘wild type’ cultures. The doubling time in growingrecA uvrBcultures is 90 min, compared to 60 min, for therecAsingle mutant and 40 min for theuvrBsingle mutant and ‘wild type’ bacteria. Growing cultures ofrecA uvrB(λcI857) bacteria contain a substantial fraction of cells which are unable to form colonies at 32 °C, but produce phage when heated to 42 °C. No such cells were found in cultures of the single mutants or the ‘wild type’ bacteria lysogenic for λc1857. The double mutant is 10 times more sensitive to ultraviolet light and twice more sensitive to mitomycin C than therecAsingle mutant. In contrast torecAbacteria, exposure of the double mutant to mitomycin C induces little additional breakdown of cellular DNA. Induction of the prophage by mitomycin C is, however, prevented in bothrecA uvrB(λ) andrecA(λ) bacteria. Exposure to mitomycin C creates conditions which render the prophage inducible by a newly transducedree Agene. This effect of mitomycin C persists and can be revealed in complete medium at 37 °C after 100 min of incubation. The decay of the prophage, in cells exposed to mitomycin C, proceeds at a similar rate in both the double mutant and therecAsingle mutant. The inability ofrecAlysogens to be induced to phage production is discussed in the light of the present findings.
Repressor-minus and operator-constitutive de-repressed mutants of F-like R factors: their effect on chromosomal transfer by HfrC
Authors: Meynell Elinor , Cooke Marylyn
Published: September 2009

Certaindrdmutants offi+R factors, when carried by strain HfrC, allowed polarized transfer of the Hfr chromosome to occur at the normal rate. These mutants were independently shown to be repressor-sensitive and so owed their de-repression to failure to produce represser (i−). With otherdrdmutants, independently shown to be repressor-insensitive (0c), the rate of polarized chromosome transfer was as low as with the wild type and only R pili were produced by the HfrC+bacteria. These R factors, therefore, continued to produce repressor and the donor behaviour of an Hfr strain depends on functioning of the integrated F.
Investigation of the mating system ofPseudodomonas aeruginosastrain I VI. Mercury resistance associated with the sex factor (FP)
Authors: Loutit J. S.
Published: September 2009

Resistance to mercury has been shown to be associated with the presence of the sex factor (FP) inPseudomonas aeniginosa. The resistance is expressed in all infected cells even though they do not necessarily function as donors.

For selection of freshly infected recipients when streptomycin or nalidixic acid were used for contra-selection of the donors, the level of mercury had to be reduced to betweenm/20000 andm/40000 when 500 units of streptomycin were present per ml and tom/40000 when 1·0 mg of nalidixic acid was included in each ml of medium. Normally donor strains would grow in the presence of Hg ions at a concentration ofm/2000, which is 10–20 times greater than the concentration in the two selective media.

The kinetics of transfer of the sex factor were investigated and it was shown that transfer began almost as soon as the cells were mixed and was completed in 20 min when 5 min were allowed for pairing.
Intragenic recombination pattern within the 164 locus ofAscobolus immersusin the presence of outside markers
Authors: Baranowska Hanna
Published: September 2009

Seven ascospore colour mutants of the 164 locus ofAscobolus immersuswere mapped, and their basic conversion frequencies established. Polarization of the sum of the basic conversion frequencies was observed. The recombination frequencies from the two-point crosses (in repulsion) are nonadditive. The influence of one mutant on the frequency of conversion of another in crosses in repulsion and coupling was pronounced. The frequency of crossing over between a pair of mutants was higher in the cross in repulsion than in coupling. A total of 535 asci containing a pair of wild-type spores were analysed from five crosses in repulsion. 193 6w:2d asci originated from the conversion of the proximal allele, 43 6w:2d asci from conversion of the distal allele and 277 asci exhibited reciprocal recombination. 54 6w:2d asci from one cross in coupling were analysed. These asci were classified and assigned to four classes: proximal allele conversion, distal allele conversion, reciprocal recombination and simultaneous conversion of wild type-alleles to mutants. In all classes of recombinant asci analysed the frequencies of additional exchanges in the adjacent intervals were higher than in random samples of asci. The wild-type chromatid was involved in the additional exchanges in the majority of crosses with a frequency exceeding 60%.
Disturbed segregation at the transferrin locus of the deer mouse
Authors: Canham Raymond P. , Birdsall D. Alan , Cameron David G.
Published: September 2009

Anomalous frequencies of transferrin phenotypes were found among the offspring of matings between deer mice heterozygous for the two forms of transferrin most common in natural populations. Matings involving other phenotypes produced offspring in the expected phenotypic frequencies. Selective penetration by facility, occurring only in the reproductive tract of the heterozygous females, appears to provide the most satisfactory explanation for the observations.
The reversible transition of certain genes inStaphylococcus aureusbetween the integrated and the extra-chromosomal state
Authors: Richmond M. H. , Johnston Joan
Published: September 2009

It is already well established inEscherichia colithat certain genes, or groups of genes, can behave as episomes—that is, they can undergo a free transition between the fully extrachromosomal state and one in which they are integrated in the bacterial chromosome (Jacob & Wollman, 1961; Broda, Beckwith & Scaife, 1964). Although this type of behaviour has been detected commonly among members of the enteric bacteria, it has never hitherto been demonstrated clearly in a Gram-positive species. This communication shows that a reversible transition of certain genes between the extrachromosomal and the integrated state can occur in some strains ofStaphylococcus aureusat least.
Brachyphalangy, an allele of extra-toes in the mouse
Authors: Johnson D. R.
Published: September 2009

Brachyphalangy (Xt/bph) is an allele of extra-toes (Xt) in linkage group XIV of the mouse. The phenotypes of both heterozygote and homozygote are distinguishable from, but similar to, those of extra-toes.
Nutritional conditional mutants ofDrosophila melanogaster
Authors: Vyse E. R. , Nash David
Published: September 2009

A small fraction of mutagen treatedXchromosomes which would appear nonlethal in the Muller-5 test carried out on a yeast-containing medium act as lethals when tested on one or other of the definedDrosophilamedia. Such mutants have been termed ‘nutritional conditionals’. The three mutants obtained in this way have been characterized genetically, but have not yet been shown to act as simple auxotrophs.
Recurrent selection. II. An experimental study with mice andDrosophila
Authors: Bowman J. C.
Published: September 2009

1. An experimental study has been made of recurrent selection to an inbred tester. A suitable inbred line is used as a tester parent, and selection is made within a non-inbred population on the individuals crossing performance with the tester line.

It is concluded that there are two situations in which recurrent selection could be profitably applied. Firstly, recurrent selection should, theoretically, be successful when applied to characters closely related to fitness which have little additive genetic variance and secondly, in cases where a character has already been subjected to individual or family selection and has reached a plateau level in that population.

2. The two experiments—i.e. recurrent selection for large litter size in mice and for low bristle number inDrosophila melanogaster—reported here are respectively an example of each of the above situations. In each experiment selection was made between males within the closed non-inbred population on the basis of the performance of their testcross progeny resulting from matings with inbred line females.

3. Initial generation hybrid performance in both experiments was not intermediate between parental performance levels and the divergence from intermediacy was away from the direction of selection.

4. In both experiments there was no evidence to suspect the presence of over dominance.

5. Response to selection was obtained in each experiment but this was close to or less than the expected response calculated on the assumption that all the variance between sires in crossing performance was additive genetic variance.

6. From these experiments it is not possible to draw any firm conclusions about the effectiveness of recurrent selection for exploiting overdominance. It is, how ever, a very inefficient way of exploiting additive genetic variance. It is suggested that more success might be obtained by careful choice of base population material used in recurrent selection.
The production of translocations in spermatogonial cells ofDrosophilaby chloroethyl methanesulphonate (CB 1506)
Authors: Watson W. A. F.
Published: September 2009

AdultDrosophilamales were injected with chloroethyl methanesulphonate and late progeny, tracing back to treated spermatogonia, were examined for sex-linked lethals and for translocations involving the X, Y, second and third chromosomes. A dose yielding about 20% sex-linked lethals produced 11 translocations in about 3500 tested chromosome sets (approx. 0·3%). This result is discussed in relation to the problem of chromosome rearrangements in different germ-cell stages.
Mutation and replication inUstilago maydis
Authors: Holliday Robin
Published: September 2009

A method is described which makes it possible to detect induced mutations in the pre-existing gene by determining whether both daughter cells of the first division after mutagenic treatment carry the mutation. The method depends on the use of diploid strains ofUstilago maydiswhich have biochemical markers in both homozygous and heterozygous condition. Cells which are induced to mutate at a homozygous locus will also occasionally undergo mitotic crossing-over. Since only mutant cells are selected, the reciprocal products of such a cross-over will not be detected if the mutation is transmitted to only one daughter cell after treatment. Mutations induced by UV light were examined in three different diploids, and with each, by use of the appropriate selective media and the replica plating technique, it was possible to detect mutant colonies which did consist of the reciprocal products of the exchange. It is deduced that a high proportion of the mutations must occur in the pre-existing gene; and a hypothesis is suggested which attempts to reconcile this conclusion with the current concept of the structure and replication of the gene.
Mutagenic effects of X-rays and formaldehyde food in spermatogenesis of Drosophila melanogaster
Authors: Slizynska H.
Published: September 2009

The structural changes induced by X-rays in cells at different stages of spermatogenesis were analysed in salivary gland chromosomes of Drosophila melanogaster and compared with the changes induced by formaldehyde added to the food (FF) of the larvae.

The different stages of spermatogenesis vary in sensitivity to X-rays when measured by the percentage of sex-linked lethals, by the percentage of spermatozoa carrying structural changes, and by the number of changes in 100 spermatozoa. The proportions of the different types of change (T, In, Rp, Df), however, are fairly similar in all stages of spermatogenesis, but entirely different from those found after FF treatment. This suggests that it is the mutagen and not the sensitive stage which is responsible for the characteristic pattern of the FF effects.

The differences between the effects of X-rays and of FF are attributed to the different proportions of potential breaks induced by these two mutagens. Evidence has been presented indicating that while most of FF induced breaks are potential (about 73%), most of the X-rays induced breaks are immediate. For the dose rate used in the present experiment (below 1000 r/min.) only a small proportion (4–10%) of breaks induced by X-rays was found to be potential.
Complementation relationships ofNeurospora ammutants in relation to their formation of abnormal varieties of glutamate dehydrogenase
Authors: Fincham J. R. S. , Stadler D. R.
Published: September 2009

Six newammutants ofNeurospora,am14–am19, with defective formation of NADP-linked glutamate dehydrogenase, were isolated following treatment of conidia with nitrous acid. This brings the number of genetically distinct and viableammutants to sixteen. Heterocaryon-compatible isolates of each of the new mutants were tested for complementation with each of the mutants previously known. A number of new complementary combinations were found which add to the complexity of the complementation map which, however, remains linear.

The mutants which show complementation aream1,am2,am3,am7,am14andam19. It has proved possible to isolate an altered form of glutamate dehydrogenase from each of these exceptam14, which appears to produce no protein fractionating like the normal enzyme. Among the non-complementing mutants,am4produces an easily-isolated inactive form of glutamate dehydrogenase. These results agree with the immunochemical findings of Roberts & Pateman (1964).

Of the mutationally altered forms of the enzyme, theam1,am2,am3andam7varieties are electrophoretically identical or closely similar to the normal protein, while theam4andam19varieties move faster towards the anode at pH 8·5,am19being the faster of the two. Theam19protein, like theam2andam3proteins previously reported on, can be activated to give some enzyme activity, but the activity obtained is much lower for this mutant than foram2oram3.

All the complementary pairs of mutants, including those involvingam19, form active enzyme varieties which have very close to normal electrophoretic properties. In several cases the complementation enzyme is less stable to heat than the wild-type enzyme.
Interference studies in Neurospora crassa and N. sitophila
Authors: Scott-Emuakpor M. B.
Published: September 2009

Tetrad data from five-point crosses involving linkage group I (mating-type chromosome) and three-point crosses involving linkage groups VI and VII of Neurospora crassa and N. sitophila have been analysed in order to detect the phenomena of chromatid and chiasma interference on a comparative basis. Marker genes were transferred from N. crassa to N. sitophila by hybridization and repeated back crossing. The details of the methods of transfer and of making crosses have been described in a previous paper (Scott-Emuakpor, 1965).
A quick and efficient method for interruption of bacterial conjugation
Authors: Low Brooks , Wood T. H.
Published: September 2009

Jacob & Wollman (1961) produced interruption of chromosome transfer during conjugation in E. coli K-12 by exposing conjugating pairs to high shear forces created by a propeller-type mixer (a Waring blendor). In our laboratory, efforts to use this method were not completely successful because of the relatively long times required to ‘blend’ each sample and the large variations from sample to sample in the efficiency of separating mating couples (‘blending efficiency’). The variations in blending efficiency were thought to be due to lack of homogeneity of mixing in the blendor chamber. We have obtained much more satisfactory results by using a vibratory mixer which shakes the entire sample chamber and thoroughly agitates all the cells. Furthermore this vibratory blendor is much easier to use and permits taking at least twice as many samples per unit time, as compared to the usual blendor method.
Order of loci on the X-chromosome of the mouse
Authors: Lyon Mary F.
Published: September 2009

The locus of the genestriated, Str, on the mouse X-chromosome, was previously reported to be on the side of tabby (Ta) away from bent-tail (Bn). Results given in the present paper show this report to have been incorrect, and that the order of loci isBn-Str-Ta-(Mo-Blo). In addition, the position of the translocation break in Searle's translocation (T1GH) has been confirmed, the order of loci with respect to T16H beingBn-T16H break-Ta-Blo.
Polarized segregation in Ascomycetes and the differential bursting of asci
Authors: Lamb B. C.
Published: September 2009

Polarized segregation was studied at theascoandtan sporeloci ofNeurospora crassaand at thegrayandhyalineloci ofSordaria fimicola. Different alleles, re-isolates and temperatures of incubation of crosses were studied with theascolocus and different temperatures of incubation with thehandgloci. The mutants were crossed with the corresponding wild-types by methods giving a considerable degree of synchrony in the development of perithecia; segregation patterns were scored from perithecia at widely differing stages of ascal maturity. Significant polarized segregation was not generally observed when little or no dehiscence had occurred from a cross but usually became readily apparent as dehiscence proceeded. This indicated that the differences in frequency between the ascal classes that had previously been interpreted as showing polarized segregation at meiosis were actually due to a post-meiotic differential bursting of asci. This bursting was studied separately from the usually concurrent pigmentation of immature asci by comparing results from asci mounted in water with those from asci in the 2 M sucrose solution which was used throughout these experiments: the differential bursting produced by mounting asci in water gave similar polarized segregation results to those from natural dehiscence. A hypothesis to account for differential bursting in physiological terms was advanced and its predictions discussed. It seems likely that cases of apparent polarized segregation described in other Ascomycetes are also due to post-meiotic phenomena.
Restricted trandsuction by bacteriophage P22 inSalmonella typhimurium
Authors: Smith-Keary P. F.
Published: September 2009

1. In the transductionpro-401 (×) + some of the transductants are surrounded by several hundred small wild-type satellite colonies; these transductants spontaneously release phage which transducespro-401 to wild-type at high frequency (HFT phage).

2. When the HFT phage is used to infectpro-401 at very low multiplicities of infection, most of the transductants are defective lysogens and segregate proline-requiring phage-sensitive derivatives; these transductants are apparently heterogenotes. At higher multiplicities of infection, or with lysogenic recipients, a higher proportion of satellited transductants is found.

3. The HFT phage preparations transduce only the proline region of the donor genome.

4. The existence is inferred of a defective P22 particle specifically incorporating the proline region of theSalmonellachromosome; these defective particles can establish themselves as prophage and confer immunity upon the infected cell, but are unable to replicate unless a normal prophage is also present. Satellited transductants are lysogenic both for a normal and defective (proline region carrying) phage, and so on lysis release transducing phage.

5. This system is compared with the λdg-galand P1-dl-lacsystems inE. coli.
A test of sexual isolation in Drosophila
Authors: Robertson Forbes W.
Published: September 2009

1. A test is described for the development of sexual isolation between a wild and a derived population of D. melanogaster adapted to a new diet, containing EDTA. Other experiments had shown that adaptation to the new diet involved genetic changes in all chromosomes. Also fitness was reversed on the alternative diets under crowded competitive conditions.

2. In three replicated trials flies from each population were used to establish paired cage populations, supplied with the medium to which each was adapted, and the pairs of cages were joined to allow restricted immigration between them. The experiment was run for about twenty-five generations.

3. After fifteen and twenty-five generations, flies were collected from each cage to provide eggs which were cultured on the alternative diets to determine how far the members of pairs of populations differed from each other and from the foundation population. There were striking differences between the sub-populations and the parent populations, attributable to immigration between the former. Judged by the differences in performance between the sub-populations, genetic differences persisted but these were minor compared with the differences between the parent populations.

4. Tests of preferential mating on the part of flies from paired sub-populations were entirely negative.

5. Fourteen generations of selection for positive assortative mating failed to provide evidence of sexual isolation between the two basic populations, adapted to different diets.

6. From these and other experiments it is inferred that sympatric divergence is improbable in a species like D. melanogaster.
Selection for a threshold character inDrosophilaII. Homeostatic behaviour on relaxation of selection
Authors: Latter B. D. H.
Published: September 2009

This paper is concerned with three related aspects of the behaviour of populations under artificial selection for increased scutellar bristle number: (i) the pattern of response on the probit scale; (ii) the homeostatic behaviour of the selection lines on relaxation of artificial selection; and (iii) correlated responses in generation interval, reproductive capacity and competitive ability. The study was designed so that linkage would be a comparatively unimportant factor in promoting correlated responses to selection, and the effects of genetic sampling from generation to generation were also reduced to a low level.

Progress from the base mean of 4·05 bristles in females to a level of almost 8 bristles has been shown to involve two distinct phases with realized heritabilities of 0·34 and 0·10 respectively, the zone of transition corresponding closely to the position of the 6/7 threshold on the underlying scale. In addition to an apparent average reduction of about 25% in the additive genetic standard deviation in phase II by comparison with phase I, the loss in response due to the opposition of natural selection has been shown to reach a maximum near the zone of separation of the two phases.

The pattern of behaviour of the populations under artificial and natural selection has suggested the presence in the base population of genes of large effect on both bristle number and reproductive fitness. There is also evidence of additional genetic variation in bristle number which is effectively neutral with respect to fitness. Continued selection for increased scutellar bristle number in large populations has been shown to reduce mean competitive ability by more than 80%.
Identity of mutant genes ‘Shrivelled’ and cataracta congenita subcapsularis in the mouse
Authors: Verrusio A. C. , Fraser F. C.
Published: September 2009

The cataract-producing mutant gene previously described as ‘Shrivelled’ appears to be a recurrence of the mutant described by Paget as cataracta congenita subcapsularis, and should henceforth be referred to as CatFr.
Skeletal polymorphism and genetic drift in a Delhi frog, Rana cyanophlictis
Authors: Grewal Manjit Singh , Dasgupta Sanjoy
Published: September 2009

Nineteen axial skeletal variants are described in the frog Rana cyanophlictis, collected from five isolated populations of Delhi. Four of these populations came from large perennial ponds and one, a transitory population, was entrapped from a temporary rain pool. The populations were found to diverge significantly from each other in the incidence of these skeletal variants. We have attributed this divergence to genetic drift, but the effects of unknown selective forces cannot be ruled out.
The differential maturation of asci and its relevance to recombination studies ofNeurospora, Sordariaand similar Ascomycetes
Authors: Lamb B. C.
Published: September 2009

Four ascospore-pigmentation mutants were crossed with their wild-types by methods giving a considerable degree of synchrony in perithecial development; segregation patterns were scored from perithecia at different stages of maturity. The observed second-division segregation frequencies forascoinN. crassawere at a maximum when little or no ascal dehiscence had occurred but decreased markedly as dehiscence proceeded. No significant change in this frequency with maturity occurred fortan sporeinNeurosporabut inS. fimicolathe observed second-division segregation frequencies forgrayandhyalinerose with increasing perithecial maturity. As similar changes in this frequency were observed when asci were mounted in water instead of the 2msucrose solution normally used, it was concluded that changes in this frequency with maturity generally resulted from a differential maturation and bursting of asci with different spore arrangements, rather than from changes in crossover frequency in successive meioses. Some evidence of the latter phenomenon was found in two of theSordariacrosses.

In a cross ofasco×rib-1 inNeurospora, the observed frequency of recombination between the two loci was significantly higher in dispersed spores collected from young perithecia than in those from more mature perithecia: this effect was probably an artifact resulting from the differential maturation and bursting of asci with different divisions of segregation forasco. In a cross ofcrisp× + inNeurospora, an excess ofcrispprogeny was obtained from dispersed spores and an excess of +-progeny from spores from harvested perithecia. These deviations from the expected 1:1 ratio forcr: + were thought to result from a differential maturation of asci with different segregation patterns forcrispand the failure of many dehiscing asci to expel all eight spores.

Hypotheses to explain the various phenomena observed were discussed. Suggestions were made concerning the avoidance of bias from the differential maturation and bursting of asci in experimental procedures used in the study of recombination and gene conversion. This bias may be responsible for some phenomena previously attributed to events at meiosis.
Selection for and against a canalized phenotype inDrosophila melanogaster
Authors: Young S. S. Y.
Published: September 2009

Selection for and against the canalized phenotype in scutellar bristles was attempted in two selection lines and a randomly selected line was used as control. The selection lines were the Decanalization line (D) and the Canalization line (N). The D line was maintained by matings of scute males (scwbl) with three scutellars with wild-type females (scwbl/yw) with five bristles, in the N line scute males with four bristles were mated with wild-type females also with four bristles, while in the C line males and females of the above genotypes were selected at random. The lines were established from a sample of flies taken from a line selected for high scutellar numbers.

After eighteen generations of selection the C line was characterized by a regression of mean bristle number without appreciable change in variance. Relative to the N line, the D population showed a lower proportion of flies having four scutellars, a higher variance in bristle numbers, and a higher proportion of four-bristle scute flies having abnormal patterns.

Two alternative hypotheses were advanced to account for the results of this experiment. The first postulated a relative change in the widths of the four-bristle canalization zones in the selection lines, while the second suggested a relative change in frequencies of specific modifier genes for scutellars in scute and in wild-type genotypes of the lines. The evidence favours the latter hypothesis.
Genetic variation in diuretic responses: further and correlated responses to selection
Authors: Stewart J. , Spickett S. G.
Published: September 2009

Three parameters of diuretic response to water-load (diuretic lag, maximum rate of diuresis and ratio of total output to input volume) have each responded to selection from a genetically heterogeneous base stock with significant realized heritabilities. Selection has been continued for ten generations and has produced mice more extreme than any of the founder strains. In the selection lines for ratio of output to input, correlated responses in salt excretion during the course of the diuresis, relative adrenal weight, the relative size of the renal medulla, and the quantity of renal collecting ducts, have been observed. These correlated responses are accounted for in terms of renal and adrenal physiology. The elucidation of the individual genetic determinants of the responses is discussed.
The recovery of tryptophan A auxotrophs at high frequency in a strain ofSalmonella typhimurium
Authors: Riyasaty S. , Dawson G. W. P.
Published: September 2009

1. Auxotrophs were sought in a slow-growing reversion of thetryA47strain ofS. typhimurium. This reversion differs fromtryA47by a genetic change that is inseparable from the47site and has been designated47S. Out of thirty-nine auxotrophs that derived from independent mutations, twenty-two grew on minimal medium supplemented with anthranilic acid. Eight of these auxotrophs were examined and each was shown to have the47Ssite unchanged and to carry a further mutation in thetryAgene. These further mutations were shown to be at different sites in different auxotrophs.

2. Auxotrophs were sought in the wild-type LT-2 strain. None out of thirty-six were mutant in thetryAgene.

3. The47Ssite intryA47Swas replaced by47+transduced from wild-type LT-2. Auxotrophs were sought in this strain and only one out of nineteen was mutant in thetryAgene.

4. Auxotrophs were sought in a wild-type reversion oftryA47. Out of twenty-six none were mutant in thetryAgene.

5. The47+site in wild-type LT-2 was replaced by47Stransduced fromtryA47S. Auxotrophs were sought in this strain and twenty-two out of fifty-five were mutant in thetryAgene.

6. We conclude thattryAauxotrophs are only recovered at a high frequency when the47Ssite is present in thetryAgene.

7. In strains with the47Ssite in thetryAgene the frequency of auxotrophs that will grow on minimal medium supplemented with indole but not on minimal medium supplemented with anthranilic acid is appreciably higher than in those strains without the47Ssite in thetryAgene. These auxotrophs are mutant in genes that are in the same operon astryA.
Relationships among interaction products in hybrids between pigeons and doves, following transfer of genes between species
Authors: LaBar Martin M. , Irwin M. R.
Published: September 2009

Following the transfer to the common pigeon (Columba livia) of a cellular antigen (Cg) fromC. guinea, and toStreptopelia risoriaof respective members of the group-8 system fromchinensisandsenegalensis, new combinations of these two antigenic systems were produced from matings ofliviaandrisoria. The hybrid substances associated with the cells of each of the five new combinations of the cellular antigens were related to each other and to the usual F1-livia/risoriacells but, with the possible exception of two, were definitely differentiated from each other. Cross-reactivities of the reagents for the hybrid substances were also observed, primarily with heterozygotes of the group-8 system ofStreptopelia. Evidence is thus provided that the interaction takes place primarily if not entirely between the genes of the C-system ofColumbaand the group-8 system ofStreptopelia.
Study of the association of resistance to two drugs in a transferable determinant inSalmonella typhimurium
Authors: Anderson E. S. , Kelemen Marianne V. , Jones Christine M. , Pitton J.-S.
Published: September 2009

A strain ofS. typhimuriumcarrying transferable determinants, one for resistance to ampicillin (A), another for resistance to streptomycin and sulphonamides (SSu), was irradiated with ultraviolet light. A clone resulting from this treatment had lost streptomycin resistance and now carried the A determinant and a new determinant, ASu. Except for coding for ampicillin resistance, the ASu determinant was homologous with SSu. The A moiety of ASu produced ampicillin (penicillin) resistance of the same degree as the original A determinant. It was therefore concluded that irradiation had resulted in the elimination of the S gene in the SSu determinant and its replacement by an A gene to form ASu. Experiments with the ASu and SSu determinants suggest that there is normally only one copy of a resistance determinant in the host cell and only one cell site into which it can integrate.
Cytogenetical studies in wheat: II. An analysis of chlorophyll abnormalities in hexaploid wheat
Authors: McIntosh R. A. , Baker E. P.
Published: September 2009

Following segregation in two unrelated wheat crosses, albinism was associated with chromosome 7B nullisomy which permitted expression of mutant genes on chromosomes other than 7B. The frequencies of albino segregante differed in the two instances, being dependent upon the morphology of the 7B monosome, which was either telocentric 7BLor normal.

Aviridisphenotype also segregated from one cross. Its expression was independent of 7B aneuploidy. Failure to obtain lines segregating only for green andviridisphenotypes was due to semi-lethality resulting from the presence of two 7B isochromosomes.
Genetic control of DNA specificity inPseudomonas aeruginosa
Authors: Rolfe B. , Holloway B. W.
Published: September 2009

Genotypic and phenotypic changes of HCM inP. aeruginosaare due to a variety of causes. In addition to interstrain genetic differences and the semi-permanent effects of growth at 43°C, mutations affecting both restriction and modification have been isolated by direct selection and through the pleiotropic effects ofp–fluorophenylalanine resistance mutations. It is suggested that some of these changes affecting HCM may be taking place through alterations of the ribosomes.
The sequence of four structural and two regulatory methionine genes in theSalmonella typhimuriumlinkage map
Authors: Ayling P. D. , Chater K. F.
Published: September 2009

Three-point transduction analysis was employed to determine the sequence of four structural and two regulatory methionine genes (metA, B, F, HandmetI, J, respectively) on two apparently adjacent transduction fragments inSalmonella typhimurium. These fragments were subsequently orientated with respect to each other and the rest of the linkage map by the analysis of recombinants obtained in conjugation experiments. The following clockwise sequence of genes is proposed: -metJ-metB-metF-argF-thi-purD-metA-metI-metH-. The bearing of these results on the regulation of themetB–FandmetA–Hclusters is discussed.
Selective enrichment of R−segregants as the main mechanism of ‘curing’ of the R factor by acridine dyes
Authors: Yoshikawa Masanosuke
Published: September 2009

By the use of appropriate strains ofEscherichia coli, Shigella flexneriandSalmonella typhimuriumwith and without an R factor, R100, the mechanism of ‘curing’ of R factor by acridine dyes was examined. This R factor was shown to confer increased sensitivity to acriflavine upon the host cells.E. colistrain W-3630, once infected with R100, has never been observed to segregate R−cells. When mixtures of R+and R−cells of this strain were grown in acriflavine broth, the proportion of R−cells increased and was also correlated with the proportion in the initial inoculum. Other bacterial strains carrying R100segregate R~ cells spontaneously. Growth tests starting with varying proportion of R+and R−cells of these strains in acriflavine broth also gave a marked correlation between the initial and final proportions of R−cells, and indicated that the main cause of ‘curing’ the R factor was the selective enrichment of R−segregants present in the initial inocula or arising spontaneously during growth of the R+culture. These results suggest that the mechanisms underlying the ‘curing’ of F and R factors are different. Tests with several acridine dyes gave results similar to those with acriflavine.
The effects of Salmonella typhimurium on derepressed mutants of F-like factors
Authors: Grindley N. D. F. , Anderson E. S. , Smith H. R. , Grindley June N.
Published: September 2009

Derepressed mutants of F-like transfer factors, isolated by mutagenesis, were characterized as repressor-minus (i−) or operator-constitutive (oc). Mutants of the i− class are derepressed in K12 but repressed in Salmonella typhimurium. They are derepressed in S. typhimurium by a kanamycin resistance determinant carrying a locus der, described previously. Most oc mutants of F-like factors are derepressed in both K 12 and S. typhimurium. However, one mutant of F-lac was oc in K12 but was repressed in S. typhimurium. It was derepressed by der. Repression by S. typhimurium is different from that by fi+ factors, since der reverses the former but does not affect the latter. Possible interpretations of these findings are discussed.
Decanalization of scutellar bristle number inDrosophila
Authors: Scowcroft W. R. , Latter B. D. H.
Published: September 2009

A major difference in developmental stability has been demonstrated between two populations produced by artificial selection for supernumerary scutellar bristles. The test system involves the substitution of an X-ray induced partial revertant ofsc1for the wild-type allele at thescutelocus, enabling direct comparisons to be made of the degree of canalization at the wild-type level of expression of the character. One population is comparable with the unselected Canberra stock in stability, though it differs appreciably in mean bristle number: the other population shows a marked reduction in the level of regulation of bristle number variability. The alleles responsible for the reduced level of canalization are rare in the base population, and are of particular importance in the determination of limits to directional selection. Their effects on developmental stability have been shown to depend on the activity of the allele at thescutelocus.
Influence of the population genetic background on the persistency of a recessive lethal inDrosophila melanogaster
Authors: Ytterborn Karl H.
Published: September 2009

In a population of Drosophila melanogaster started from an inbred wild-type strain the recessive second chromosome lethal studied had shown overdominance which after many generations was lost. In the present study the persistence of this lethal was tested in three series each of five populations. The genetic backgrounds of the different series of populations were obtained from (a) the inbred strain, (b) the above original population after the overdominance had been lost, and (c) a population started from the same inbred strain and where another lethal had shown overdominance which subsequently had been lost. The lethal was overdominant in the (a) background but detrimental to the heterozygous carriers on the other backgrounds. The detrimental effect of the lethal was stronger in the (b) background than in the (c) background. The varying behaviour of the lethal is possibly due to different adapted background genotypes and/or different degrees of heterozygosity of the gene pools.
I-like resistance factors with thefi+character
Authors: Grindley June N. , Anderson E. S.
Published: September 2009

Thefi+(fertility inhibition+) property was originally described in R factors related to F (F-like factors). The originalfi−factors, in contrast, were related to the transfer factor of a colicin I factor (I-like factors). We describe here a group of R factors which arefi+but I-like. It is suggested that all the termsfi+,fi−, F-like and I-like be used in the description of transferable plasmids.