bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the distribution of recessive embryonic lethals in a natural population ofCoelopa frigida(Fab.)
Authors: Burnet B. 
Published: September 2009

An account is given of the habitat and ecology of a wrackbed population ofCoelopa frigida(Fab.). The spatial distribution of the third-instar larvae was found to be patchy. This is due to a preference of adult flies for oviposition sites in zones of high temperature within the wrackbed. The relationship between larval density and temperature was found to account only in part for the patchy distribution, a second factor being the formation of family aggregates within each temperature zone. The effect of this type of spatial distribution on the interpretation of genetic sampling methods for the population is discussed.Samples of third-instar larvae from the wrackbed population have been analysed for the presence of recessive embryonic lethals in three consecutive years from 1957 to 1959. From a total of 528 gametes tested, 44 recessive embryonic lethals were isolated. Cross tests for allelism showed that certain lethals were repeated within samples taken in the same year.The gross frequency of embryonic lethals is shown to be independent of seasonal changes in population density. Estimates of gene frequency are made for certain individual lethals and these are shown to be greater than expected on the basis of the census size of the population. Possible causes of this discrepancy are examined.
Nutritional requirements of inbred lines and crosses ofDrosophila melanogaster
Authors: Sang James H. 
Published: September 2009

1. The problem of whether or not hybrids are more efficient, less variable and have less stringent nutritional needs than their parents is examined by finding the dose-responses of four inbredDrosophilalines and their crosses to casein, choline, RNA, riboflavine, nicotinic acid, pyridoxine and folic acid, under germ-free conditions.2. Under more or less optimal conditions, survival, development rate and weight of the hybrids are generally superior to those of the inbreds; the 4-way cross is not inferior to the 2-way crosses. Variability of the crosses is not necessarily lower than that of the inbreds, and the 4-way cross is no more variable than the 2-way crosses.3. As measured by growth rate, the hybrids use casein more effectively than the pure lines, but their relative efficiency declines as the casein supply is decreased. There is a positive correlation between casein requirements for optimal growth and minimum requirements of pyridoxine. Hybrids also tend to be more efficient in their use of choline, but not of the other nutrients examined.4. Deficiencies of particular nutrients (and also of excess provision of the non-vitamins) affect the lines and crosses differently, so that their relationships to one another are altered. The hybrids show no special advantage in resisting departures from the optimum. Variability is also changed significantly under sub-optimal conditions and, in some situations, the hybrids may then be more variable than the inbreds.5. Each line and each cross is found to have its own optimal nutritional environment, and its particular reactions to departure from this. The full potential of the genotypes cannot be manifest, therefore, by tests in a single, standard environment.
The effect of initial reverse selection upon total selection response
Authors: Allan J. S. , Robertson Alan 
Published: September 2009

A computer has been used to investigate the effect of an initial period of reverse selection on the subsequent response of a population to renewed forward selection with the same population size and selection intensity. As the computer was used to derive gene frequency distributions, there was no random element in the results obtained. A theoretical solution to the problem was obtained for genes with small effects.The process can be adequately described by the duration of the reverse selection (expressed in terms of the population sizeN), the product of population size and gene effect,Ns, and the initial gene frequency. If the duration of reverse selection,t, is less thanN/2, the loss in selection advance due to the reverse selection is roughlyt/N, though slightly greater than this for genes with low frequency. The ‘point of no return’ after which it is impossible, with the same population size and selection intensity, to return even to the starting frequency is 1·4Ngenerations for genes with small effect and this declines as the gene effect increases.Some extension of results to recessive genes is also given.
The parasexual cycle inVerticillium albo-atrum
Authors: Hastie A. C. 
Published: September 2009

Genetic recombination through the parasexual cycle, or some very similar system, was demonstrated. Diploid strains were very unstable, yielding about 95% haploid conidia from three-week-old cultures This high frequency of haploid segregants was at least partly attributable to greater sporulation of haploid mycelium, but may also reflect a higher frequency of haploidization than that found inAspergillus nidulans.Mitotic crossing-over also occurred frequently, and gave segregants homozygous for some markers but heterozygous for others. It was also detectable by changes in the phase of linked markers occurring during vegetative growth. Some heterozygous segregants were either aneuploids, or were formed by double mitotic crossovers.Haploid segregants, derived from nuclei which had previously undergone mitotic crossing-over, were often recovered. This coincidence of mitotic crossing-over and haploidization in one nuclear lineage, together with the probable occurrence of double mitotic crossovers, makes mitotic analysis less clear cut than inAspergillus nidulans.
On one of the formulae proposed for interpreting transduction data
Authors: Dawson G. W. P. 
Published: September 2009

The paper on the analysis of data from transduction experiments with Salmonella typhimurium, which was published in Genetical Research (Dawson, 1963), unfortunately contained an error on p. 419. In calculating the limiting values X/Y, the formulae for d and d′ are correctly stated, but their solutions are transposed. The last and third last lines on p. 419 should therefore be interchanged. In the arithmetic example on pp. 420 and 421, a similar interchange of the calculations of d and d′ is necessary. The maximum value of a/b is then:and the calculation of the minimum value should be:These values of 2·20 and 1·23 are to be compared with the values of 2·23 and 1·24 in the published paper.
Hyphal fusions in the wood-rotting fungusSchizophyllum commune: I. The effects of incompatibility factors
Authors: Ahmad Sayed S. , Miles Philip G. 
Published: September 2009

SUMMARYEffects of the incompatibility factors inSchizophyllum communeFries on the process of hyphal fusion are described. A role for the A incompatibility factor in hyphal fusion is indicated. Matings between strains with different mating types have higher fusion frequencies than matings between strains with the same mating types. Evidence is presented that the differences in fusion frequencies are not due to genetical factors other than mating types. When two strains of different mating types are grown in the same culture plate, but separated by a cellophane membrane, the strains are altered in some unexplained manner in such a way that even matings between strains of the same mating type have a higher fusion frequency than occurs in matings between compatible strains not so treated. Matings leading to the formation of common-B and dikaryotic mycelia have comparable fusion frequencies while those leading to the formation of common-A mycelia have a far lower frequency of fusions. It has been demonstrated that high fusion frequency is associated with heterozygosity at the A locus. It is suggested that a repression–derepression mechanism involving a cell wall degrading enzyme or enzymes may be involved in the regulation of hyphal fusion.
Lethal interactions of theeye-goneandeyelessmutants inDrosophila melanogaster
Authors: Hunt David M. 
Published: September 2009

SUMMARYA synthetic lethal system involving homozygous combination of the non-allelic eye mutantseye-goneandeyelessis described. The major lethal crisis is towards the end of the pupal instar although a number of double homozygotes die at pupation. The pupal lethal crisis can be overcome in a number of individuals by the experimental removal of the operculum from differentiated pupae. However, only a few of the resulting enclosed double homozygotes proved fully viable, the remainder dying almost immediately after emergence. Dissection of the surviving adults revealed that the brain is located in the anterior thorax.
Gene conversion: observations on the DNA hybrid models
Authors: Paszewski Andrzej 
Published: September 2009

SUMMARYSome features of gene conversion in fungi and their bearing on the hybrid DNA models are discussed. Available experimental data from tetrad analysis seem to give a more complex picture of polarity in intra-genic recombination and of the relations between conversion and post-meiotic segregation, and between conversion and crossing-over, than predicted by the models.A new hypothesis of the mechanism of gene conversion with special attention given to the aspect of asymmetry in this phenomenon is proposed as an alternative to the mechanism suggested by the DNA hybrid models.
Variations in enzyme phenotypes and their underlying genotypes among wild strains of the genusNeurospora
Authors: Grindle M. , Davis R. H. 
Published: September 2009

SUMMARYTwenty-three exotic strains of four species ofNeurospora(N. crassa, N. sitophila, N. intermediaandN. tetrasperma) were grown in minimal medium and their enzyme phenotypes were compared. The exotic strains did not differ substantially with respect to the specific activities of the biosynthetic enzymes, ornithine transcarbamylase (OTC), carbamyl phosphokinase and aspartate transcarbamylase. Exotic strains ofN. crassaandN. sitophilawere crossed with laboratory mutants ofN. crassato determine whether there were significant differences among the exotic strains in the gene complexes underlying their enzyme phenotypes. Most of the exotic strains carried similar OTC structural genes and similar genetic modifiers of OTC activity: their OTC structural genes were expressed normally in the genomes of the parent strains, in the alien genomes of standard laboratory mutants and in the mixed genomes of parent × mutant hybrids. One exoticN. crassacarried a distinctive OTC structural gene that elevated OTC activity when transferred into the genome of a standard laboratory mutant. A second exoticN. crassacarried distinctive genetic modifiers of OTC activity: two mutations,c-andhi, interacted in the exotic parent to normalize OTC activity and rate of growth, buthiled to extremely high OTC activities and to a reduction in rate of growth when separated fromc-by interstrain recombination.
The length of time required for a selectively neutral mutant to reach fixation through random frequency drift in a finite population
Authors: Kimura Motoo 
Published: September 2009

SUMMARYFrequency distribution of the length of time until fixation (excluding the cases of eventual loss) of a selectively neutral mutant in a finite population was obtained. With 4Negenerations (Ne, effective population size) as the unit length of time, the distribution has mean μ1= 1, standard deviation σ = 0·538, skewness γ1= 1·67 and kurtosis γ2= 4·51 (see Fig. 1).
A genetic study of cold resistance in wheat
Authors: Law C. N. , Jenkins G. 
Published: September 2009

SUMMARYThe variety Chinese Spring ofTriticum aestivumis susceptible to cold treatment applied at the juvenile plant stage, while the variety Cappelle-Desprez shows resistance to such treatment. By cytological and backcross procedures single homologous pairs of chromosomes from Cappelle-Desprez were substituted for their homologues in Chinese Spring. Assay experiments carried out on each of the 21 possible substitution lines indicated that three chromosomes, 4D, 5D and 7A of Cappelle-Desprez were involved in the determination of cold resistance. The resistance expressed by the three substitution lines carrying these chromosomes was less than the reaction of Cappelle-Desprez to cold treatment. Also the magnitude of this resistance supported a hypothesis that the action of the three chromosomes was additive on the scale of measurement used. The possible relationships of the genes for cold resistance to the established genes controlling other developmental characters, also carried by these three chromosomes, are discussed.
The reduction in fitness from genetic drift at heterotic loci in small populations
Authors: Robertson Alan 
Published: September 2009

SUMMARYIn finite populations, loci maintained segregating by hétérozygote superiority will be disturbed from their equilibrium positions by genetic sampling and the mean fitness of individuals will consequently be reduced. A general expression for this reduction is obtained for the segregation of two alleles. If the probability of continued segregation at the locus is high, the reduction tends to 1/4N, irrespective of the strength of selection, whereNis the effective population size. This will always be much less than the segregation load. Ifnalleles are segregating, so that all heterozygotes have the same fitness, the reduction tends to (n−1)/4N.
Selection for a threshold character inDrosophila: III. Genetic control of variability in plateaued populations
Authors: Latter B. D. H. 
Published: September 2009

SUMMARYAn analysis of populations ofDrosophila melanogasterwhich had ceased to respond to selection for increased scutellar bristle number has disclosed the existence of an overall negative genetic correlation between replicate lines in the frequency of the two major component bristle types, viz. anteriors and posteriors. Negative phenotypic correlations among component bristle sites have also been detectedwithinpopulations. A model involving competition among sites for the available resources of a particular limiting substrate is therefore proposed. Genetic changes have been effected in exceptional populations which lead either to an increase in the rate of production of the limiting substrate, or to a lowering of the concentration of the substrate necessary for bristle initiation. The allelic substitutions concerned are recessive, and have been described asdecanalizingalleles in view of their effects on both bristle number variability and a measure of developmental regulation at individual anterior sites. Genetic variation has also been demonstrated for the mean allocation of resources to each of the four component bristle types, viz. anteriore interstitials, posteriors and apicals. A brief discussion is given of the implications of the model for breeding practice in domestic species.
A system generating spontaneous intrachromosomal changes at mitosis inAspergillus nidulans
Authors: Nga B. H. , Roper J. A. 
Published: September 2009

Previous studies had shown that haploid strains ofAspergillus nidulanswhich have a chromosome segment in duplicate are unstable at mitosis. Through the study of various haploid and diploid strains, with and without translocations and with balanced and unbalanced genomes, it has been shown: (1) that imbalance of chromosome segments is responsible for instability, and (2) that the chromosomal deletions produced are confined solely or largely to the segments which provoke instability.The term ‘mitotic non-conformity’ has been proposed for this instability phenomenon. An explanation for it has been sought in terms of attachment sites, limited in number and specific for chromosome segments, at which replication is initiated.
Effect of inhibition of DNA synthesis on u.v. sensitive Bs strains ofEscherichia coli
Authors: Green Michael H. L. , Donch John , Chung Young S. , Greenberg Joseph 
Published: September 2009

The effect of nalidixic acid, a specific inhibitor of DNA synthesis, onEscherichia colistrain B (lon) and its u.v.-sensitive derivatives is examined. Strain B itself is sensitive to nalidixic acid, whereas its u.v.-resistant derivative B/r is resistant.It is shown that in allexr Astrains, in which u.v.-induced filamentation is suppressed, resistance to nalidixic acid is increased. Amongexr Astrains, Bs4 is exceptionally resistant to nalidixic acid. This is because nalidixic acid kills only growing cells and strain Bs4, atryauxotroph, may grow poorly under the conditions used to test nalidixic acid.Theuvrgenes of the HCR strains Bs1, Bs8 and Bs12 do not suppress u.v.-induced filamentation nor do they affect the response to nalidixic acid. Theuvrgene of strain Bs3 is unusual in increasing the tendency to filament and also sensitivity to nalidixic acid.Strains Bs1, Bs3 and Bs8 are all doubly mutated from strain B, the second mutation (notuvr) being responsible for their increased resistance to nalidixic acid as well as partially or completely suppressing filamentation.It is concluded that the cell division mechanism of (lon) strain B is sensitive to inhibition of DNA synthesis. Mutations which suppress the tendency of strain B to filament reduce its sensitivity to inhibition of DNA synthesis.
Chromosomal basis of dosage compensation inDrosophila: I. Cellular autonomy of hyperactivity of the maleX-chromosome in salivary glands and sex differentiation
Authors: Lakhotia S. C. , Mukherjee A. S. 
Published: September 2009

Morphology and the rate of RNA synthesis of theX-chromosome inXX/XOmosaic larval salivary glands ofDrosophila melanogasterhave been examined. For this purpose the unstable ring-Xwas utilized to produceXXandXOnuclei in the same pair of glands. The width of theX-chromosome and the left arm of the 3rd chromosome (3L) of larval salivary glands was measured and the rate of RNA synthesis by them was studied upon the use of [3H]uridine autoradiography in suchXX(female) andXO(male) nuclei developing in a female background (i.e. otherwise genotypicallyXX). In such mosaic glands the width of the singleX-chromosome of male nuclei is nearly as great as that of the paired twoX's of female nuclei, as is also the case in normal male (X Y) and female (XX). The singleXof male nuclei synthesizes RNA at a rate equal to that of the paired twoX's of female nuclei and nearly twice that of an unpairedXofXXnuclei. Neither the developmental physiology of the sex nor the proportion ofXOnuclei in a pair of mosaic salivary glands of anXXlarva has any influence on these two characteristics of the maleX-chromosome.It is suggested that dosage compensation inDrosophilais achieved chiefly, if not fully, by a hyperactivity of the maleX, in contrast to the singleXinactivation in female mammals, that this hyperactivity of the maleXis expressed visibly in the morphology and metabolic activity of theX-chromosome in the larval salivary glands of the male, and that this hyperactivity and therefore dosage compensation inDrosophilain general is not dependent on sex-differentiation, but is a function of the doses of theX-chromosome itself.
Correlated meiotic and mitotic maps inAspergillus amstelodami
Authors: Lewis L. A. 
Published: September 2009

Thirteen markers inAspergillus amstelodamiwere mapped through meiotic and mitotic recombination, resulting in good correlation of the two linkage groups established by each method. Mapping via mitotic analysis proved the more efficient of the methods because of the long distances between some of the markers established in this organism.Visual selection of haploid segregants from mitotic recombination was aided by the ability to recover conidia which differed in colour from the haploid parents. These contained pairs of conidial colour markers which were not epistatic to each other.
Mitotic non-conformity inAspergillus: successive and transposable genetic changes
Authors: Azevedo J. L. , Roper J. A. 
Published: September 2009

SUMMARYStrains ofAspergillus nidulanswith, a duplicate chromosome segment are mitotically unstable; in addition to phenotypically improved variants, arising following deletions in either duplicate segment, they give morphologically deteriorated types, some with, enhanced stability. In one isolate, deterioration and increased instability were determined by mutation in a duplicate segment; a more stable derivative no longer had this mutation but had one in another linkage group. Another variant, too unstable for analysis, gave derivatives whose single, new mutations were in different linkage groups. It is proposed that deterioration and increased instability result from tandem duplications on either duplicate segment; transposition of these to non-duplicated regions reduces instability. Another 17 variants had a single new mutation each; mutations, possibly clustered, occurred in all linkage groups. In these strains perhaps transposition preceded analysis. Deteriorated variants gave lineages of types with morphological changes caused by further, superimposed mutations. This continued instability is explained as interaction, in fidelity of replication, of non-homologous chromosome segments.Instability inA. nidulansstems from chromosome imbalance. As imbalance is known or suspected in other cases of instability it may be possible to show common mechanisms for apparently diverse phenomena.
Genetic loads at a polymorphic locus which is maintained by frequency-dependent selection
Authors: Kimura Motoo , Ohta Tomoko 
Published: September 2009

SUMMARYIf a polymorphic locus is maintained in finite populations by frequency-dependent selection with selective neutrality at equilibrium, it is generally accompanied by two genetic loads, i.e. the dysmetric and the drift loads. The former arises because the fitness of the population may not be at a maximum at the equilibrium gene frequency and the latter because genetic drift in small populations displaces the gene frequency from its equilibrium value.In some simple models of frequency-dependent selection considered, the drift load is independent of selection coefficients and is approximately equal to (n−1)/(2Ne), wherenis the number of alleles andNeis the effective population size.
Transfer characteristics of two resistance determinants in a wild strain ofKlebsiella aerogenes(V9A)
Authors: Reeve E. C. R. 
Published: September 2009

SUMMARYKlebsiella aerogenesstrain V9A carries determinants AKand TK, giving resistance to ampicillin and tetracycline, and a plasmid FKlac, but no active sex factor. F− and I-type sex factors were able to transfer TKfrom V9A toEscherichia coliK12 and between strains of K12, and TKbehaved as a separate plasmid with its own replicon. AKcould not be transferred, except possibly by a sex factor carrying its own A determinant, but the evidence for such transfer was inconclusive. It is suggested that AKis either a chromosomal gene or is in a plasmid with a cell attachment inKlebsiellanot represented inE. coliK12. AKproduces a β-lactamase.
Derepression of F-lacinSalmonella typhimuriumby a determinant for kanamycin resistance
Authors: Smith H. R. , Grindley June N. , Grindley N. D. F. , Anderson E. S. 
Published: September 2009

SUMMARYWhen a determinant for neomycin-kanamycin resistance (K) was transferred by an F-lacfactor intoSalmonella typhimurium, the resulting KF-lacstrain was sensitive to the male-specific phage μ2and F-lacwas derepressed. However, F-lacalone is repressed inS. typhimurium. When kanamycin resistance is spontaneously lost fromS. typhimuriumKF-lacan element persists which derepresses F-lacinS. typhimurium. The results are consistent with the hypothesis that a locusder, for derepression of F-lacinS. typhimurium, lies on the K plasmid. The R factor Rldrd19 is derepressed in K12 but is repressed inS. typhimurium. It also is derepressed byder. In contrast to F-lacand R1, another R factor, R136drdH8, is derepressed in both K12 andS. typhimurium, so that the intervention ofderis unnecessary for its derepression in the salmonella host.