bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the fixation probability of mutant genes in a subdivided population
Authors: Maruyama Takeo 
Published: September 2009

SUMMARYFollowing 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.
Investigation of the mating system ofPseudodomonas aeruginosastrain I VI. Mercury resistance associated with the sex factor (FP)
Authors: Loutit J. S. 
Published: September 2009

SUMMARYResistance 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

SUMMARYSeven 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

SUMMARYAnomalous 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.
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.
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.
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%.
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.
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.
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.
Selective enrichment of R−segregants as the main mechanism of ‘curing’ of the R factor by acridine dyes
Authors: Yoshikawa Masanosuke 
Published: September 2009

SUMMARYBy 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

SUMMARYDerepressed 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.