bluuebunny/crossref_metadata_2025 huggingface dataset:
The regulation of NADL-glutamate dehydrogenase inAspergillus nidulans
Authors: Kinghorn J. R. , Pateman J. A.
Published: September 2009

Wild-type cells ofAspergillus nidulanshave undetectable NADL-glutamate dehydrogenase activity when utilizing glucose and high levels of NADL-glutamate dehydrogenase when utilizing certain amino acids as sole carbon sources.

A mutant, designatedgdhCl, has appreciable NAD-GDH activity when utilizing glucose as a carbon source. ThegdhC1mutation is semi-dominant and is located in linkage group III.
The order of replication of chromosomal markers inPseudomonas aeruginosastrain 1: I. Marker frequency analysis by transduction
Authors: Booker R. J. , Loutit J. S.
Published: September 2009

The generalized transducing phage F116 has been used to prepare lysates from fast- and slow-growing cultures ofPseudomonas aeruginosastrain 1. These lysates have been used to transduce a number of auxotrophic markers to prototrophy and the ratios of the numbers of transductants obtained with each lysate have been determined. Since the markers are those which have been mapped by conjugation in previous studies it has been possible to compare the ratios obtained for each marker with the relative position of the marker on the chromosome map. If the assumption is made that there is only one circular chromosome inP. aeruginosastrain 1 it is possible to suggest a way in which two apparently unlinked segments might be joined together. It is also possible to suggest that the chromosome replicates sequentially in two directions from a fixed origin.
exrB: amalB-linked gene inEscherichia coliB involved in sensitivity to radiation and filament formation
Authors: Greenberg Joseph , Berends Leonard J. , Donch John , Green Michael H. L.
Published: September 2009

PAM 26, a radiation-sensitive mutant ofEscherichia colistrain B, is described. Its properties are attributable to a mutation in a gene,exrB, which is cotransducible withmalB. It differs fromuvrA(alsomalB-linked) derivatives of strain B in being sensitive to 1-methyl-3-nitro-1-nitroso-guanidine and γ-radiation, and in being able to reactivate UV-irradiated phage T3. It differs fromexrA(alsomalB-linked) derivatives of strain B in forming filaments during the course of normal growth as well as after irradiation. WhenexrBwas transduced into a K12 (lon+) strain, filaments did not form spontaneously. Three-point transductions established the order of markers asmet A malB exrB. Based on an analysis of the frequency of wild-type recombinants in a reciprocal transduction betweenexrAandexrBstrains, it was inferred that they are not isogenic and that the order of markers ismalB exrA exrB.
Detrimental genes with partial selfing and effects on a neutral locus
Authors: Ohta Tomoko , Cockerham C. Clark
Published: September 2009

Gene and genotypic frequencies for a deleterious mutant in mutation selection balance are derived for an infinite population undergoing partial self-fertilization. These provide formulations of mean survival and the mutational load. Obtained also are the average number of mutant genes and affected individuals stemming from a single mutant.

As a concomitant effect on frequencies at a neutral locus the mutational load is distributed disproportionately among the neutral genotypes. For partially recessive mutant genes on the 1, 1-sh, 1-sscale, the effect is to increase the frequency of the heterozygote and to decrease the frequencies of homozygotes at the neutral locus relative to the frequencies expected with complete neutrality. This apparent overdominance at the neutral locus has been shown to be connected with identity disequilibrium rather than linkage disequilibrium. It increases generally assandhdecrease, and as the proportion of self-fertilization and the degree of linkage increase. The apparent overdominance with complete linkage is generally less than double that for free recombination. For partially dominant mutant genes,h≥ ½, the effects on the frequencies of heterozygote and homozygotes at the neutral locus are reversed.
Additive and non-additive genetic variance in odontometric traits in crosses of seven inbred lines of house mice
Authors: Leamy Larry J. , Touchberry R. W.
Published: September 2009

A least-squares diallel analysis of the offspring of crosses of seven inbred lines of house mice was performed for the mean widths of the second (M2) and third (M3) mandibular molars. Significant differences among lines, as well as between inbreds and hybrids (positive heterosis) were found for these characters. Estimates of the heritabilities (from general combining ability variances) were high for both teeth as were estimates of maternal effects. Specific combining ability and reciprocal effects were significant only for the M3. Additionally, X-irradiation reduced the mean number of individuals per litter, and thereby indirectly influenced the widths of both molars.
Mitochondrial mutations affecting resistance to erythromycin and mikamycin inParamecium aurelia: provisional results with a new method
Authors: Queiroz Clara , Beale G. H.
Published: September 2009

A new method for obtaining mitochondrial mutants ofParamecium aureliais described. Sensitive organisms were first placed in medium containing a low concentration (0·02 mg/ml) of erythromycin (ERY), insufficient to prevent fission. The paramecia were then transferred through a graded series of increasing ERY concentrations, with a period of growth at each concentration. A high yield of ERY-resistant mutants was obtained.

Continuous growth in 0·02 mg/ml ERY also resulted in the accumulation of a spectrum of mutants resistant to various concentrations of ERY. Many of these mutants are also resistant to mikamycin. On returning the resistant paramecia to media lacking ERY, some clones remained resistant whilst others reverted to sensitivity.
Inversion polymorphism in a two-locus genetic system
Authors: Charlesworth Brian
Published: September 2009

The types of equilibria possible with an inversion in a two-locus system are considered, and their stability properties investigated. With complete suppression of crossing-over in inversion heterozygotes, there are three possible types of stable equilibria; which of these is reached by a new inversion depends on the fitness effects of the two loci concerned. With one of these equilibria, basically involving cumulative overdominance of the selected loci, the inverted and standard sequences are genetically homogeneous and differ with respect to both loci. With the other types of equilibrium, the standard sequence remains heterogeneous for one or both loci. It is shown that this situation may lead to variations in karyotypic fitnesses when the inversion is changing in frequency. It is also found that, with certain fitness relationships, two alternative stable equilibria may coexist; the final frequency reached by an inversion may therefore depend on the population's history.

The effects of double crossing-over in inversion heterozygotes were also investigated, and it was shown that the equilibria with double crossing-over are closely related to the corresponding equilibria without it, except that both sequences are more heterogeneous genetically. Within each sequence there is almost complete linkage equilibrium between the selected loci, although both are in linkage disequilibrium with the inversion itself. It was also found that, with double crossing-over, the population tends to remain for many thousands of generations in a state of quasi-equilibrium. In this state, the inversion tends not to return to its original frequency after a perturbation; also, it may remain for a long time relatively homogeneous genetically, especially when rare.

These results were compared with those from experiments and observations on inversion polymorphisms.
Position effect variegation in the mouse
Authors: Cattanach Bruce M.
Published: September 2009

Position effect variegation has been studied in female mice heterozygous for thefleckedX-autosome translocation, T(7;X)Ct. Some of these carried the spotting gene (s) which clarifies the variegated patterns. Others carried a second X-autosome translocation, T(X; 16)16H, which suppresses the randomness of X-chromosome activity.

It was found the position effect variegation stems primarily from early occurring events which lead to the formation of clones of cells with different phenotypes. In this respect the phenomenon appears to parallel that found inDrosophila. However, in the mouse, late-occurring events are also found which can only be readily accounted for by the reactivation of previously inactive loci. They occur, not only during foetal development, but throughout the life-time of the animals and in a manner which suggests they derive from a progressive retreat of the inactivating influence of the heterochromaticXchromosome back along the attached autosome towards the breakpoint. It is proposed that the early occurring events do not lay down fixed programmes of gene suppression, as proposed forDrosophila, but that, like the later-occurring events, they represent the reactivation of previously inactivated loci. The possibility that this might also be true forDrosophilais discussed.

The study also provided evidence favouring the view that theX-chromosome controlling element, Xce, modifies the heterozygous phenotypes ofX-linked genes by biasing the randomness of the X-inactivation process, rather than by operating through cell selection mechanisms. The data also support and extend Mintz's (1967) concept of pigment pattern differentiation.
The effects of mutantp-alleles on the reproductive system in mice
Authors: Melvold Roger W.
Published: September 2009

Thep6H,p25H, andpbsalleles at the pink-eyed dilution locus in mice (Mus musculus) cause sterility in males and semi-fertility in females when homozygous, while thepd, pun, p, and + alleles do not reduce fertility. Pituitaries from sterile males had significantly lower proportions of gonadotropic cells than pituitaries from fertile males. Ovaries from semi-fertile females contained large numbers of developing follicles, but no corpora lutea or corpora hemorrhagica were found. The proportion of polyovular follicles in ovaries of semifertile females was abnormally high.

Pituitary gonadotropins appear to be reduced in the sterile genotypes although the lesion cannot be localized. Possible relationships between these and other pleiotropic effects of mutantp-alleles are discussed.
The use of bacteriophages for differentiating plasmids ofPseudomonas aeruginosa
Authors: Krishnapillai V.
Published: September 2009

Six bacteriophages have been used in the classification of 19 plasmids (antibiotic resistance-mediating R factors and FP sex factors which promote host chromosome transfer) ofP. aeruginosaisolated in different geographical regions. On the basis of phage-plating responses on isogenic strains of bacteria differing only in the plasmids carried, five groups of plasmids were distinguishable. In general the groups could be correlated with their geographical origin although differences between plasmids from the same region were found. The unique phage-plating responses were also useful in establishing the possible identity of plasmids isolated from the same original strain and given different designations by independent investigators. The classification of the plasmids derived here on the basis of phage-plating responses could be correlated with classifications based upon other phenotypic characteristics described elsewhere. The nature of inhibition of plating of phages B39 and G101 by R18–1 and R18–3 respectively was shown to be due to interference with some aspect of intra-cellular phage replication rather than to plasmid-mediated restriction.
Cytogenetic and complementation analyses of recessive lethal mutations induced in theXchromosome ofDrosophilaby three alkylating agents
Authors: Lim J. K. , Snyder L. A.
Published: September 2009

Salivary-gland chromosomes of 54 methyl methanesulphonate- and 50 triethylene melamine-inducedX-chromosome recessive lethals inDrosophila melanogasterwere analysed. Two of the lethals induced by the mono-functional agent and 11 of those induced by the polyfunctional agent were found to be associated with detectable aberrations. A complementation analysis was also done on 82 ethyl methanesulphonate- and 34 triethylene melamine-induced recessive lethals in thezeste-whiteregion of theXchromosome. The EMS-induced lethals were found to represent lesions affecting only single cistrons. Each of the 14 cistrons in the region known to mutate to a lethal state was represented by mutant alleles, but in widely different frequencies. Seven of the TEM-induced lethals were associated with deletions, only one of which had both breakpoints within the mapped region. Twenty-six of the 27 mutations in which only single cistrons were affected were mapped to 7 of the 14 known loci. One TEM- and two EMS-induced mutations were alleles representing a previously undetected locus in thezeste-whiteregion.
Bare-patches, a new sex-linked gene in the mouse, associated with a high production ofXOfemales: II. Investigations into the nature and mechanism of theXOproduction
Authors: Phillips Rita J. S. , Kaufman M. H.
Published: September 2009

The highXOproduction inBpa+ mouse stocks appears to be due, not toBpaitself, but to a closely linked factor for highXOproduction (Fxo) which may be a gene or a chromosomal aberration. The change ofBpa FxotoBpanon-Fxooccurs with a frequency of about 6%; the reciprocal change fromBpa FxotoFxonon-Bpahas not been found. There is some evidence thatFxomight involve a structural alteration such as an inversion or a deletion. TheX-chromosome loss is due to non-disjunction which occurs in about one-third of the oocytes, probably mainly at meiosis I. Frequencies of other chromosomal abnormalities found in the stocks are given.
Mitochondrial genetics, circular DNA and the mechanism of thepetitemutation in yeast
Authors: Clark-Walker G. D. , Gabor Miklos George L.
Published: September 2009

We propose a general hypothesis involving properties of circular DNA which can explain such phenomena as thepetitemutation, suppressiveness, and the polarity observed in mitochondrial recombination in the yeastSaccharomyces cerevisiae. This hypothesis involves excision and insertion events between circular DNA molecules as well as structural rearrangements in the DNA generated by these events. The special properties of circular DNA have been considered in analysing recombination, and a number of results are obtained which are not intuitively apparent.

This hypothesis can be applied to any situation involving circular DNA such as bacterial plasmids and cytoplasmic circular DNAs, where the opportunity exists for recombination and rearrangement events.
Interactions between the surface exclusion systems of some F-like plasmids
Authors: Willetts Neil , Maule John
Published: September 2009

Four surface exclusion systems have been identified amongst a group of F-like plasmids inE. coli: SfxI(F), SfxII(ColV2 and R538-1fin−), SfxIII(ColVBtrpand R1-19) and SfxIV(R100-1 and R136fin−). None of these systems was expressed in stationary phase cells or, except for ColVBtrp, duringfin+transfer inhibition, showing that the surface exclusion gene(s) is usually co-controlled with the transfer genes.

Recipient cells carrying two plasmids specifying different surface exclusion systems did not always express both of these: the overall pattern suggested that the four systems and/or their sites of action are related. There was no surface exclusion between donor cells carrying two plasmids determining different surface exclusion systems and recipient cells carrying a plasmid determining either one of these. Our hypothesis to explain this and other results is that surface exclusion prevents interaction between the tip of the pilus on the donor cell and a receptor site on the recipient cell surface. Pili (probably mixed) with two types of tips would be present on cells carrying two different plasmids, the one unresponsive to the single surface exclusion system of the recipient cells allowing transfer of both plasmids.
A genetic study of female sterility inNeurospora crassa
Authors: Mylyk Orest M. , Threlkeld S. F. H.
Published: September 2009

A genetic analysis following the initial detection of a female sterile variant resulted in the finding of seven or eight different female sterile mutants, most or all of which are on linkage groups I and II. They were present in heterokaryotic condition in already existing strains, except one which originated spontaneously during the study. All mutants fail to produce functional protoperithecia. Most of them, however, are able to function as female parents in heterokaryons. All mutants differ morphologically from the wild type, most being subtly different, but two being appreciably different. The apparently high frequency of occurrence of female sterile mutants suggests that protoperithecial development is under an elaborate genetic control. Differences in vegetative morphology appear to be a common property of mutants affecting the early stages of the sexual development.
Population structure in artificial selection: studies with Drosophila melanogaster
Authors: Madalena F. E. , Robertson Alan
Published: September 2009

The effect of sub-dividing a population during selection was studied by selecting downwards for sternopleural bristles in Drosophila melanogaster. The four structures used all involved the selection of 40 individuals out of 200 measured in each sex. The alternatives were:

(i) one large line with the same selection procedure in all generations,

(ii) eight small lines with the same procedure in all generations,

(iii) the ‘single cycle’ structure in which large lines derived from crosses between selected small lines at either the sixth or twelth generation, and,

(iv) the ‘repeated cycle’ structure in which the best five small lines were mixed at the sixth generation of selection to produce a new set of small lines on which the procedure was repeated for a total of three cycles.

Of the first two methods, the large line had a higher final response than did any of the small lines. The latter, selected with an intensity of 5 out of 25 in each sex, had lower average final response than had a similar group of lines selected from the same base population with the lower intensity of 10/25. The results showed no clear effect of the sub-dicision of the population, followed by selection between lines, though they were in general agreement with theortical expectations. Several second chromosome recessive lethals were found at high frequencies in different selected lines. One of these, found in eight of the lines, had an effect on bristles in the heterzygote of about 1·5 phenotypic standard deviations. The evidence strongly suggests a pleiotropic effect on bristle score.
Genetic analysis of larval feeding behaviour inDrosophila melanogaster
Authors: Sewell David , Burnet Barrie , Connolly Kevin
Published: September 2009

The larvae ofDrosophila melanogasterfeed continuously during their period of development. The rate of feeding activity, measured as the number of cephalopharyngeal retractions per minute, varies with the physiological age of the larva. Feeding rate responded readily to directional selection to give rise to non-overlapping populations with fast and slow feeding larvae, respectively. Realized heritabilities for the character from different selected lines varied between 11 and 21%. Crosses between the selected populations show significant dominance for fast feeding rate and appreciable non-allelic gene interaction. Larvae of the slow feeding populations showed a correlated reduction in locomotor activity but fast feeding larvae do not move about significantly faster than the unselected controls. Asymmetry of the correlated response to selection, it is argued, is due to selection in the slow feeding populations of alleles with a secondary effect in both behaviours.
Genetic studies on male sterility of hybrids between laboratory and wild mice (Mus musculusL.)
Authors: Forejt J. , Iványi P.
Published: September 2009

The genetic control of the sterility of male hybrids between certain laboratory and wild mice (Mus musculusL.) is investigated. The observed sterility is, by definition, hybrid sterility since both parental forms (i.e. wild and laboratory mice) are fully fertile, their male offspring displaying small testes with arrest of spermatogenesis at the stage of spermatogenesis or primary spermatocytes. Results of genetic analysis as well as the failure to detect any chromosomal rearrangements point to a genie rather than a chromosomal type of hybrid sterility.

Fifty-three wild males were classified into three sets, after mating with C57BL/10 inbred females, according to the fertility of their male progeny (set I – only sterile sons; set II – only fertile sons; set III – both fertile and sterile sons). The wild males of set I, which yield only sterile male offspring with C57BL/10 females, sire sterile sons also with females of the following inbred strains: A/Ph, BALB/c, DBA/1, and AKR/J, whereas the same wild males produce fertile offspring with females of C3H/Di, CBA/J, P/J, I/St and F/St inbred strains.

The described hybrid sterility seems to be under the control of several independently segregating genes, one of them (proposed symbol Hst-1) being localized on chromosome 17 (linkage group IX), 6 cM distally from dominantT(Brachyury). A chance to search for the mechanism of hybrid sterility is provided by the finding of two laboratory inbred strains, C57BL/10 and C3H/Di, differing with respect to theHybrid sterilitygenetic system only at theHst-1 gene.

Hst-1 is closely linked but apparently not identical with the sterility factor of recessive t alleles of theTlocus.
Further observations on the hairpin-tail (Thp) mutation in the mouse
Authors: Johnson D. R.
Published: September 2009

The hairpin-tail allele (Thp) of brachyury (T) on chromosome 17 of the mouse is unique in that the phenotype of heterozygous offspring depends on which parent contributed theThp.The present paper offers formal proof of this fact using theth2allele ofTas a marker, and discusses possible modes of action of the hairpin allele.
Physiological genetics of melanotic tumours inDrosophila melanogaster: VIII. The role of choline in the expression of the tumour genetu bwand of its suppressor,su-tu
Authors: Sparrow John C. , Sang James H.
Published: September 2009

The melanotic tumour genetu bwofDrosophila melanogasterhas a specific suppressorsu-tu. The genotypestu bw; +su-tuandtu bw; su-tushow opposite responses, as measured by tumour penetrance, to increasing choline levels in the defined axenic medium. The three major metabolic functions of choline have been examined using additions to the axenic medium to determine which biochemical pathway(s) are different in the two genotypes. It is concluded that the opposite strain responses are due to changes in the pattern of phospholipid synthesis, and that the gene product of thesu-tugene probably functions in this area of metabolism.
Aberrant ascus genotypes from crosses involving mutants at theglocus inSordaria fimicola
Authors: Kitani Y. , Whitehouse H. L. K.
Published: September 2009

The genotypes are given of over 4500 asci showing aberrant segregation at the grey (g) spore colour locus inSordaria fimicolafrom crosses, with outside markers present, betweenglocus mutants and wild type, or involving pairs ofglocus mutants that differed in spore colour (glocus mutants range from grey to hyaline). This colour difference enabled asci with aberrant segregation of the mutant spore colours to be detected in the two-point crosses, as well as those with wild-type (black) spores. From a total of 21 one-point crosses involving altogether seven primary and two secondaryglocus mutants, 2700 aberrant asci have been grouped into the 14 ascus genotypes that can be recognized, and in the two-point crosses 1830 asci (1044 fully scored) from 10 pairwise combinations of the mutants have been classified into the 150 ascus genotypes that can be distinguished.
The induction of ouabain-resistant mutants by N-methyl-N′-nitro-N-nitrosoguanidine in Chinese hamster cells
Authors: Davies Peter J. , Parry Jim
Published: September 2009

Clones of V79 Chinese hamster cells resistant to the steroid compound ouabain have been induced by mutagen treatment with MNNG (= N-methyl-N′-nitro-N-nitrosoguanidine). The frequency of resistant colonies was increased from spontaneous value of 2 × 10−6 to a frequency of 1·2 × 10−3 with MNNG treatment.

The highest number of induced mutants appeared when an expression time pf 40 h was allowed between MNNG treatment and addition of ouabain.
Footpad bristles: a convenient metric character in mice
Authors: Festing Michael F. W.
Published: September 2009

A new metric character in mice, ‘footpad bristle number’ is described. The character is easily measured under a stereo-microscope, is very highly inherited, and is independent of age, sex and the environment common to littermates. Such a character might prove useful in a number of quantitative genetic studies in mice.
Phenotypic characterization of R-factor tetracycline resistance determinants
Authors: Foster T. J. , Walsh Áine
Published: September 2009

The tetracycline-resistance determinants of R-factors from different compatibility groups have been tested inEscherichia coliK12 and phenotypically classified into two major classes. Class I determinants confer high-level resistance to tetracycline (> 100 μg/ml) and moderate resistance to minocycline (5–25 μg/ml) while those of Class II gave moderate resistance to tetracycline (50–70 μg/ml) and low resistance to minocycline. Each class was subdivided because of variation in resistance profiles and in the abilities of tetracycline and minocycline to induce increased resistance. Strains carrying two compatible TetrR-factors of the same or different phenotypic groups did not show increased tetracycline resistance.
A deterministic model of cyclical selection
Authors: Hoekstra Rolf F.
Published: September 2009

A deterministic model of cyclical selection in randomly mating populations is studied. Sufficient conditions for a protected polymorphism, which are for the special case of alternating selection also necessary conditions, are obtained using a simple graphical approach. The most important condition requires ‘marginal overdominance’ (Wallace, 1968); the other conditions seem hard to satisfy in a natural situation. Furthermore it is shown that the cyclical selection model can be regarded as a special case of a frequency-dependent selection model (Cockerhamet al.1972). Using this property, a mean fitness function for the cyclical selection model is derived. Generally, the mean fitness will not be maximized under cyclical selection. The relevance of the model to the problem of the role of cyclical selection in the maintenance of genetic polymorphism in natural populations is discussed. It is concluded that this relevance is probably rather limited with regard to the creation of protected polymorphism, but that the influence of cyclical selection on transient polymorphisms might be more significant. An approximate formula for the time needed for a given change in gene frequency under cyclical selection is derived. It appears that cyclical selection can extend considerably the time during which a transient polymorphism persists, especially if the selective differences in the different environments are of the same order of magnitude and of opposite sign.
The effect of different selection intensities on selection response in egg-laying ofTribolium castaneum
Authors: Ruano R. G. , Orozco F. , López-Fanjul C.
Published: September 2009

An experiment was carried out to test the effect of varying selection intensity on the response to individual selection with a fixed number of individuals scored per generation. The selected trait was egg laying of virgin females ofTribolium castaneumscored from the 7th to the 1 lth day after adult emergence. Five different selected proportions of females were considered (5, 10, 20, 33 and 50%) and each treatment was represented by two replicate lines. Control lines were maintained throughout the experiment. The lines selected at the lowest proportions (5 and 10%) led to the largest initial gains, but the largest final gains were achieved, by the lines where the proportions selected were 10 and 20%, in agreement with theory. Lines where the proportion selected was 50% gave the lowest rate of response over the period considered (32 generations). A good agreement was found between predicted and realized short-term responses to selection. Prediction at later stages of selection deteriorated in the most strongly selected lines mainly due to the levels of inbreeding attained.
The dominance ofexrBoverexrB+in heterodiploids ofEscherichia coli
Authors: Greenberg Joseph , Donch John , Berends Leonard
Published: September 2009

To test whetherexrB, a mutation inEscherichia coliB making this strain sensitive to ultraviolet radiation and unable to divide normally, is dominant toexrB+, merodiploids were constructed by crossing HfrexrB metA+his× F−malB met A thr proA recA. metA+recombinants were fertile (F′) and sensitive to UV. One of these, F′exrB proA, was crossed with an F−metA malB thr, selecting formetA+proA+. All such progeny acquiringmalB+were UV-sensitive, fertile and segregatedmet malUV-resistant progeny. They were, therefore, meriodiploids, F′exrB/exrB+.exrBis dominant toexrB+, in which respect it resemblesexrA(lex).
Protein variation in strains of mice differing in body size
Authors: Garnett I. , Falconer D. S.
Published: September 2009

Nine (41%) of the 22 enzymic and non-enzymic loci examined in a strain of mice divergently selected for six-week body weight (six lines selected in each direction and six controls) were found to be polymorphic. The degree of polymorphism varied between the replicates from a maximum of 38% to a minimum of 14% with an average individual heterozygous at 7·7% of its loci. There was no obvious association between any of the isozyme variants and body size. The frequency distribution among the 18 lines was adequately accounted for by random genetic drift. However, an association was observed between body size and theHbblocus; theHbbsallele was found to be fixed in all of the six Large lines. An examination of the variance of gene frequencies at this locus excluded random genetic drift as an explanation for the fixation.
Location of genes for the utilization of acetamide, histidine and proline on the chromosome ofPseudomonas aeruginosa
Authors: Day Martin , Potts J. Rowland , Clarke Patricia H.
Published: September 2009

Interrupted mating methods were used to map the positions on thechromosomeof genes for the utilization of acetamide, histidine and proline. An entry time of 22 min was found for aputmarker determining the utilization of proline. Two groups ofhutmutants were studied. Mutationhut-109 was located at 18 min and mutationhutU108, which results in a defect in urocanase activity, mapped at 28 min.hutUwas shown by transduction with bacteriophage F116 to be linked toser-3 but not tomet-28 andilv-202, giving a map order ofhutU-ser-3-ilv-202-met-28.

The amidase genes were assigned an entry time of 65–75 min. A method is described for examining late entry markers by interrupted mating.
Extensions to the model of an infinite number of selectively neutral alleles in a finite population
Authors: Avery P. J.
Published: September 2009

The model, suggested by Ohta & Kimura, of an infinite number of selectively neutral alleles, in which alleles can only mutate to neighbouring alleles, has been extended to include a migratory pattern. The stepping-stone and island models of migration have been considered. In the latter case, it has been found that as the number of colonies becomes large, the expected number of alleles,ne, becomes approximately equal to

wheremis the migration rate,vis the mutation rate andNeis the effective size of each population. This solution tends to that of Ohta & Kimura asm→ 0 but one can see that for any appreciable value ofNem, a large increase inneis obtained. In order to check the validity of iterative results, models with a finite number of alleles have been considered, and their solutions have been found to converge quickly to those of the infinite case. The results exemplify the great power of migratory structure and neutral alleles to maintain a large amount of heterozygosity. Double step mutation and the finite time solution have also been considered.
Fitness of third chromosome homozygotes inDrosophila melanogaster
Authors: Sved J. A.
Published: September 2009

A population cage experiment has been carried out to estimate fitness for a sample of fourteen non-lethal third chromosomes inD. melanogaster. This measurement, which should take into account all aspects of fitness, gives an estimated mean fitness of chromosome homozygotes of approximately ten percent.
Cytofluorimetric evidence for meiosis in gametangial nuclei of Phytophthora drechsleri
Authors: Mortimer A. Martin , Shaw David S.
Published: September 2009

Relative DNA contents of samples of nuclei from hyphal tips and from gametangia at different stages of development have been obtained by cytofluorimetry. The occurrence of nuclei with 4C, 2C and 1C DNA complements in gametangia and mainly 2C complements in hyphae indicates that meiosis takes place in the gametangia of Phytophthora drechsleri.
Trimethoprim-resistant mutants ofE. coliK12: preliminary genetic mapping
Authors: Breeze A. S. , Sims P. , Stacey K. A.
Published: September 2009

Trimethoprim-resistant mutants ofE. coliK12 have been isolated by-serial subculture in progressively higher concentrations of trimethoprim. High-level resistance depends on the accumulation of several mutational changes. Transduction with bacteriophage P1 has shown that all the mutations involved in resistance are associated with a locus, to be calledtmr, betweenpyr AandpdxAand closely linked topdxA. Resistance is accompanied by, and presumably due to, an increased activity of the target enzyme, dihydrofolate reductase. Thetmrlocus may include the structural gene for dihydrofolate reductase but the only mutations that have so far been observed are concerned with regulation.
The replication of the chromosome of Pseudomonas aeruginosa strain 1: II. Sequential mutagenesis of synchronized cultures
Authors: Booker R. J. , Loutit J. S.
Published: September 2009

The order of replication of a series of genes in Pseudomonas aeruginosa has been studied in synchronized cultures using a method based on the technique of sequential mutagenesis. This technique relies on the increased susceptibility of the replication point of the bacterial chromosome to mutagenesis by N-methyl-N′-nitro-N-nitrosoguanidine. The genes studied were those previously mapped by conjugation and whose order of replication had been studied by an investigation of gene frequencies in exponential populations. The results are consistent with the idea that there is two-way replication of the chromosome of P. aeruginosa starting at a point near trp-1 and arg-6. They also confirm that the two linkage groups which have been found by conjugation replicate at different times. If the assumption is made that there is only one chromosome in P. aeruginosa, the results can be used to show how the two linkage groups may possibly be joined together and the order is such that there would have to be two sites of attachment for the sex factor FP2.
Drift variances of heterozygosity and genetic distance in transient states
Authors: Li Wen-Hsiung , Nei Masatoshi
Published: September 2009

Using the moments of gene frequencies, the drift variances of heterozygosity and genetic distance in transient states have been studied under the assumption that all mutations are selectively neutral. Interestingly, this approach provides a simple derivation of Stewart's formula for the variance of heterozygosity at steady state. The results obtained indicate that if all alleles in the initial population are equally frequent, the standard derivation of heterozygosity is very small and increases linearly with time in the early generations. On the other hand, if the initial allele frequencies deviate appreciably from equality, then the standard deviation in the early generations is much larger but increases linearly with the square root of time. Under certain conditions, the standard deviation of genetic distance also increases linearly with time. Numerical computations have shown that the standard deviations of heterozygosity and genetic distance relative to their means are so large that a large number of loci must be used in estimating the average heterozygosity and genetic distance per locus.
Evidence for a new kind of regulatory gene controlling expression of genes for morphogenesis during the cell cycle inUstilago violacea
Authors: Day A. W. , Cummins J. E.
Published: September 2009

The first part of the paper provides strong supportive evidence for the previous findings (Cummins & Day, 1973; Day & Cummins, 1973) that the two alleles of the mating-type locus of the basidiomyceteUstilago violaceahave different periods of inducibility during a cell cycle, and that the cell cycle characteristics of each allele are maintained in freshly isolated diploids. This difference in temporal properties of the alleles appears to be the basis of the dominance of allele a2as it is inducible during a phase of the cell cycle when allele a1is non-inducible. During G1both alleles appear to be inducible and apparently ‘neutralize’ each other so that the cell cannot mate.

The second part of the paper provides evidence for a unique genetic control mechanism. The evidence suggests that the period of cell cycle inducibility of a locus governing a morphogenetic pathway may be regulated by a separate control gene thecclocus, with two known allelesccstr(a stringent or restricted period of inducibility) andccrel(a relaxed or non-restricted period of inducibility). This hypothesis stems from analysis of a diploid that wasa1·ccstr/a2·ccreland showed dominance of allelea2during the S and G2phases when freshly isolated, but which became incapable of mating after a period of subculturing. Analysis of haploids derived from this diploid strain showed that both mating-type alleles were functional but that it was now homozygous forccstr, i.e. of genotypea1·ccstr/a2·ccstr· Thus the temporal and functional aspects of the mating type alleles are determined by different loci. It is postulated that cell cycle control loci may be widespread and serve to regulate the action of genes concerned with morphogenesis in relation to other cell cycle events.
The genetics ofPhycomyces blakesleeanus
Authors: Cerdá-Olmedo E.
Published: September 2009

The genetic relationship between germspores and parental mycelia has been investigated in crosses involving multiply-marked heterokaryons and in simple difactor crosses.

It is concluded that for each zygospore the number of different diploid nuclei undergoing meiosis is often more than one, but generally not more than two. The meiotic products divide to produce the nuclei in the usually uninucleate germspore primordia and then continue dividing to produce germspores. Unmated nuclei do not pass directly from parents to progeny.

Each germsporangium contains differing numbers of viable germspores, with an average of about 7000; different genotypes are represented by varied numbers of germspores and often expected genotypes are missing. When the results of several germsporangia are added together or germspore stocks from many germsporangia are analysed, reciprocal genotypes appear in equal numbers and reliable recombination frequencies may be calculated.
The effect of selected linked locus on heterozygosity of neutral alleles (the hitch-hiking effect)
Authors: Ohta Tomoko , Kimura Motoo
Published: September 2009

A diffusion model was developed to investigate the effect of a mutant substitution by natural selection on heterozygosity at a linked neutral locus. Using this theory, we made extensive numerical analyses to compute the expected total heterozygosity (i.e. the sum of the fraction of heterozygotes over all generations until fixation or loss) at the neutral locus. It was shown that the hitch-hiking effect is generally unimportant as a mechanism for reducing heterozygosity. The effect becomes significant only when the recombination fraction between the selected and the neutral marker loci is smaller than the selection coefficient. In order to check the validity of the mathematical theory, Monte Carlo experiments were performed, and the results were in agreement. It has been suggested that linkage is important only in transient small populations such as at the time of speciation.
The probability of survival of a mutant gene in an age-structured population and implications for the evolution of life-histories
Authors: Charlesworth Brian , Williamson John A.
Published: September 2009

An expression is derived for determining the probability of survival of a new favourable mutation in a large random-mating population with overlapping generations. For a gene of small effect, in a near-stationary population, an approximate formula similar to the usual one for discrete generations is obtained. The implications of these results for the evolution of life histories are discussed, using the partial derivatives of the chance of survival of a gene, with respect to changes in age-specific fecundities and survival probabilities. The properties of these derivatives are very similar to those of the derivatives of the intrinsic rate of increase, analysed by Hamilton (1966), thus providing a genetical basis for his conclusions concerning the evolution of life histories.
Manganese mutagenesis in yeast: II. Conditions of induction and characteristics of mitochondrial respiratory deficientSaccharomyces cerevisiaemutants induced with manganese and cobalt
Authors: Prazmo Wieslawa , Balbin Ewa , Baranowska Hanna , Ejchart Anna , Putrament Aleksandra
Published: September 2009

Manganese and cobalt are capable of inducing ρ−mutations* in non-growing cells ofSaccharomyces cerevisiae, but their mutagenic action is much stronger in growing cells. At a given concentration cobalt and manganese can be either strongly mutagenic or non-mutagenic, depending on the cell density.

Most of the ρ−mutants induced with manganese and a considerable proportion of those induced with cobalt are suppressive and/or transmit drug resistance markers, so they must still carry mitochondrial DNA. Cobalt can decrease suppressiveness with low efficiency and eliminate drug resistance markers from established ρ−clones.
The distributions of the combinations of the sexes in mammalian litters
Authors: James William H.
Published: September 2009

There is subnormal dispersion in the distributions of the combinations of the sexes in some samples of litters of pigs, rabbits and mice. For instance, consider litters of exactly size 8. As contrasted with binomial expectation, there are too many with exactly 4 males and 4 females, and too few unisexual litters. It is argued that this supports the hypothesis (independently proposed by the author and by Guerrero) that P, the probability that a zygote will be male, varies with the time at which it is formed within the cycle. It is noted that data of Kaufman seem to support the hypothesis.
Cell lineage analysis of kynurenine producing organs inDrosophila melanogaster
Authors: Nissani Moti
Published: September 2009

Six hundred and ten gynandromorphs were produced in which anXchromosome loss uncovered the vermilion mutation. The mosaic patterns observed indicate that wild type ocelli are incapable of kynurenine production and that, in addition to the eyes, postembryonic kynurenine producing cells originate from two separate regions of the blastoderm. The positions of these regions on the genetic fate map ofDrosophila melanogastercorrespond to the embryonic precursors which give rise to the kynurenine producing cells of the larval fat body and Malpighian tubes.
A factor on a wild third chromosome (IIIRa) that modifies the Segregation Distortion phenomenon inDrosophila melanogaster
Authors: Trippa G. , Loverre A.
Published: September 2009

IIIRais a genetic modifier of Segregation Distortion (SD) inDrosophila melanogaster, which was discovered in the same natural population from Ranna (Sicily) that carriedSDRa. It is located at 49·7 ± 0·8 on chromosome III.IIIRawas found to have a dominant effect on segregation distortion which varied with the origin of theSDchromosome tested. Thus it enhanced the level of distortion caused by 14SDchromosomes from seven natural populations in Southern Italy and Sicily, but decreased the level of distortion caused bySDR−1, a chromosome from a natural population near Rome. Moreover,IIIRadetermined or enhanced the distorting effect ofSDRain males heterozygous forSDRaand variousSD+wild chromosomes differently sensitive toSDRa. The frequency of chromosomes having an effect likeIIIRachromosome was very high (around 70%) in samples from two natural populations of Southern Italy tested-those of Ranna and Corato. No effects ofIIIRaother than its ability to modify SD have been detected.
Use of isozymes as chromosome markers in wheat-rye addition lines and in triticale
Authors: Tang K. S. , Hart G. E.
Published: September 2009

The alcohol dehydrogenase (ADH), glutamate oxaloacetate transaminase (GOT), acid phosphatase (ACPH), endopeptidase (EP) and aminopeptidase (AMP) zymogram phenotypes of Chinese Spring wheat, Imperial rye, the Chinese Spring-Imperial triticale and the series of seven disomic Imperial chromosome additions to Chinese Spring were determined. It was found that the zymogram phenotypes produced for one or more of the enzymes by each of the Imperial chromosomes 3, 6, C and D differ sufficiently from that of Chinese Spring so as to provide evidence for the presence or absence of each of these chromosomes in addition lines and triticales. The structural genes Got-R2 and Got-R3 were located in Imperial chromosomes 6 and 3 respectively and other genes involved in the production of GOT in chromosomes C and D. By analysis of GOT alone, evidence for the presence or absence of Imperial chromosomes 3, 6, C and D in addition lines and triticales can be obtained. Adh-R1 was located in chromosome C and a gene(s) involved in the production of an ACPH was located in chromosome D.

The linkages obtained for Got-R2, Got-R3 and Adh-R1 demonstrate homoeology between the Imperial chromosomes 3, 6 and C and the Chinese Spring chromosomes of groups 3, 6 and 4 respectively. The discovery that Adh-R1 is located in Imperial chromosome C also suggests that the 4R/7R and 7R/4R homoeologous groupings proposed elsewhere for the chromosomes of the rye cultivars Imperial, Dakold, and King II should be reassessed, since they are inconsistent with the known linkages of Adh-R1 in the three cultivars. The finding in King II of two forms of ADH and of two ADH genes has been reported. The results of our study of Imperial, King II, and Dakold indicate that rye possesses but one ADH and only one ADH structural gene.
Linkage relationships of markers on chromosome 17 of the house mouse
Authors: Hammerberg Graig , Klein Jan
Published: September 2009

Linkage data for the following markers on chromosome 17 of the house mouse were obtained: centromere (marked by translocationR67),Brachyury(T),tufted(tf),H-2, andthin fur(thf). The markers were found to be arranged in that order in the genetic map and the combined genetic distances between individual markers were found to be as follows:Rb7…T, 4·5 cM;T…tf, 5·8 cM;tf…H-2, 5·0 cM;H-2…thf, 15·1 cM. The localization of thethflocus on the non-centromeric side of theH-2complex provides an important marker for this arm of chromosome 17. The map distances in the centromeric portion of chromosome 17 changed drastically in the presence of varioustfactors. These factors strongly reduce the recombination frequency in theT…tfandtf…H-2intervals and this crossing-over suppression is most likely responsible for the linkage disequilibrium betweentandH-2reported earlier. Recombinants involving atchromosome but occurring to the right of theH-2complex do not change the properties oftfactors suggesting that all determinants responsible for the t phenotype are located in the chromosomal region betweenTandtf(H-2).