bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetic control of the kinetics of mouse spermatogenesis
Authors: Bruce W. Robert , Furrer Rudolf , Goldberg Robert B. , Meistrich Marvin L. , Mintz Beatrice
Published: September 2009

The kinetics of spermatogenesis in the mouse, and the possible genetic controls, have been investigated in different genotypes by means of the method of velocity sedimentation at unit gravity to separate testis cells and nuclei labelled with tritiated thymidine. The progression of the radioactivity through different sedimentation classes of cells provides a measure of their kinetics. The results demonstrate kinetic differences at the stage of spermatocyte differentiation between the C57BL/6 and AKR inbred strains of Mus musculus musculus and in randombred mice of the subspecies Mus m. molossinus. These kinetic differences are controlled by genetic factors which are not linked to the Y chromosome. The relevant autosomal alleles of C57BL/6 are dominant over those of AKR in F1 hybrids.
Definition of the blue mutant phenotype and its genetic basis inSaccharomyces cerevisiae
Authors: de G. Mitchell I. , Bevan E. A.
Published: September 2009

Mutant colonies of yeast are described which varied in colour from blue to green and in intensity of colour when grown on medium containing methylene blue. Blue mutant colonies contained more dead cells, decolorized redox dyes more slowly, had a higher respiratory quotient on glucose containing medium, and absorbed more methylene blue dye than did wild-type. The blue colony phenotype was induced both spontaneously and at high frequency by ultraviolet light and ethylmethane-sulphonate in both haploid and diploid strains. Many of the light-coloured colonies isolated following mutagenic treatment reverted to wild-type when subcultured but most dark-coloured colonies remained stable. Stable blue mutants were shown to arise by mutation of many separate nuclear genes in haploids and were often caused by recessive lethals in diploids.
Variation in the basal level of alkaline phosphatase inCoprinus lagopuswild-type strains
Authors: North Jane , Lewis D.
Published: September 2009

Two wild-type strains ofCoprinus lagopusisolated from a single basidiocarp differ by a factor of two in their basal level of alkaline phosphatase. The gene responsible for this difference is allelic toreg-2and unlinked to thepholoci; the allele conferring a lower basal level is dominant both in diploids and dikaryons.
The three locus model with multiplicative fitness values
Authors: Strobeck Curtis
Published: September 2009

The necessary and sufficient conditions for the stability of the equilibrium point with no linkage disequilibrium are obtained for the three locus model with multiplicative fitnesses. It is shown that there are six inequalities that must be satisfied in order for this equilibrium to be stable. Three of the inequalities require that there be heterozygotic superiority at all loci. The other three are exactly those inequalities which are required for each pair of loci to be stable with linkage equilibrium if they are considered to be an isolated two locus system. Thus, all the information needed to determine the stability of this equilibrium with three loci is contained in one and two locus theory.
Genetic studies of class 2 nonsense suppressors inEscherichia coli
Authors: Rothwell M. Anne , Green Michael H. L. , Bridges Bryn A.
Published: September 2009

Three genetically distinct ochre suppressors have been identified in a strain ofEscherichia coliB/r, all of which suppress a tyrosine auxotrophy and classify as class 2 by phage suppression pattern. One ochre suppressor, which was obtained by conversion from a class 2 amber suppressor, and a second ochre suppressor obtained directly from the non-suppressing parent, were found to have separate map locations, though a peculiar phenotype with regard to a leucine auxotrophy is exhibited by strains carrying either suppressor. We suggest that both suppressors correspond to separate genes for glutamine-insertingtRNA. A Leu+mutant of a strain carrying one of these suppressors was studied and was found to contain a further nonsense suppressor having amber-suppressing activity at a reduced level. We suggest that this suppressor might result from a mutation in another part of the translational machinery concerned with glutamine insertion. The third ochre suppressor has no effect on the leucine auxotrophy and mapping data suggest that it may besupL, an ochre suppressor probably inserting a different amino acid, from glutamine.
Aeruginocin tolerant mutants ofPseudomonas aeruginosa
Authors: Holloway B. W. , Rossiter Heidi , Burgess Diana , Dodge Judy
Published: September 2009

Mutants ofPseudomonas aeruginosatolerant to the action of trypsinsensitive aeruginocins can be readily isolated. They are found to be heterogeneous for a range of phenotypic characteristics (including the pattern of membrane protein components in polyacrylamide gel electrophoresis), response to bacteriophages (including both plaque formation and the ability to be lysogenized), sensitivity to various toxic agents, colonial morphology, and cellular morphology. The nature of these changes strongly supports the view that the mutants examined have undergone alteration in membrane structure. A limited genetic analysis indicates that at least two chromosomal regions are involved.
Protein and nucleic acid metabolism in organs from mice selected for larger and smaller body size
Authors: Priestley G. C. , Robertson Moira S. M.
Published: September 2009

Studies of the growth and composition of Q-strain mice selected over 20 generations for high and low body weight at 6 weeks of age, and their unselected controls, were made on livers and kidneys of males from the five selection replicates A, B, C, D and F. Differences in growth rate between Large and Small QD mice were confirmed from 2 to 9 weeks of age, but were greatest in the third, fourth, sixth and seventh weeks. Total amounts of dry matter, protein, free amino acids, bulk RNA and ribosomes were increased or decreased from control values in proportion to organ weight. A less-perfect relationship between DNA content and organ weight suggested that some small changes in average cell mass had accompanied the main change in cell number in organs from the selected lines. Absorbance profiles of polyribosomes from both organs were identical in selected and control mice: selection had not operated on the proportion of single (currently inactive) ribosomes. Attempts to relate the observed differences in growth rate in QD mice to differences in the rate of protein synthesis produced an unexpected result: incorporation of radioactively labelled amino acids was consistently higher in the organs of the Small mice. Measurements of rates of protein turnover, and calculated rates of protein degradation, suggested that protein might also be degraded more rapidly in the small mice.
Replicated selection for body weight in mice
Authors: Falconer D. S.
Published: September 2009

The variation in the response to selection was studied by replication of selected lines. A random-bred strain of mice was divided into six replicates. Two-way selection for 6-week weight was applied in an identical manner to each replicate, and each had an unselected control. Each line (6 large, 6 control, 6 small) was maintained by minimal inbreeding with 8 single-pair matings. The overall mean responses, both up and down, were linear and very regular for ten generations, with realized heritabilities of 40% upwards, 33% downwards and 37% for the divergence. The separate replicates, however, differed greatly in their realized heritabilities, with upward selection ranging from 25 to 46%, and downward selection from 16 to 50%. The theoretical prediction that, because of genetic drift, the standard error of a realized heritability is underestimated by the standard error of the regression of response on cumulated selection differential was borne out in this experiment. The empirical standard error, calculated from the observed variance between replicates, was more than twice as great as that of the regression. The empirical standard errors showed that the asymmetry between upward and downward responses was not significant. The variation between the replicates was ascribed mainly to random drift, which may seriously influence the conclusions about the realized heritability and the asymmetry of response that would be drawn from a single experiment with the population size of one of these replicates. After 23 generations of selection the large lines were approaching limits, and the limit appeared to be at the same level in all. The small lines showed an undiminished realized heritability after 23 generations, but the selection differentials were then so small that little progress was made. There was evidence of counter-acting natural selection. All aspects of productivity – proportion of fertile matings, litter size and weaning rate – declined in the control lines. The overall productivity of the large lines was a little below the controls, and that of the small lines was reduced to about half the level of the controls. The separate replicates differed from each other significantly in all the components of productivity.
A case of chromosome dissociation in a shrew
Authors: Olert J.
Published: September 2009

A male common shrew trapped at Bonn/BRD was found to have a karyotype differing from the normal karyotype by a dissociation of a large metacentric chromosome. Similar findings are hitherto unknown in mammals.
Lac+plasmids are responsible for the strong lactose-positive phenotype found in many strains ofKlebsiellaspecies
Authors: Reeve E. C. R. , Braithwaite J. A.
Published: September 2009

A variety ofKlebsiellastrains examined all show either a strong (ML+) or a weak (ML−/+) lactose-positive phenotype on MacConkey agar. ML+Klebsiellae have about 10 times the β-galactosidase activity of ML−/+strains in cultures both induced and not induced for this enzyme. Of 14 ML+strains of diverse origin tested, at least 13 carry alacoperon on a plasmid which can be transferred toEscherichia coli. The seven plasmids so far studied in detail all belong to the F compatibility group but are unable to promote their own transfer. To explain these results it is suggested that theKlebsiellagroup derive from a common ancestor with a chromosomallacoperon of low efficiency, which was made good by the acquisition of alacoperon from another bacterial strain, probablyE. coli: the newlacgenes remained as a plasmid, possibly because they could not be integrated in the new host.
Simultaneous selection for two correlated traits inTribolium
Authors: Bell A. E. , Burris Martin J.
Published: September 2009

Simultaneous selection byindependent culling levelsof two correlated traits in all four combinations of directions was investigated withTriboliumin a replicated experiment extending over nine generations. In addition to the two primary traits, 13-day larval weight and pupal weight, four secondary traits (pupation time, adult emergence time, adult weight and larval number) were observed.

The observed responses for both selected and unselected traits agreed with theoretical expectations after the latter were adjusted for changes which occurred in genetic and phenotypic parameters. Phenotypio variances for the selected traits were correlated positively with population means, yet genetic variances and heritabilities declined in all selected populations. No change was detected in the genetic correlation between selected traits even though the divergent two-trait selection was designed especially to ‘break’ the positive correlation of + 0·55 ± 0·12 present in the base population.

Striking changes in growth and developmental patterns resulting from the divergent selection were discussed in terms of metamorphic limits and ‘stabilizing’ genetic correlations.
Transfer-positive J-independent revertants of the F factor inEscherichia coliK 12
Authors: Achtman Mark
Published: September 2009

Cells carryingtraJ−mutants of F are transfer-deficient and are good recipients in conjugation (Achtman, Willets & Clark, 1972). In addition, thetraJgene product is involved in pilus- and in plasmid-specificity (Willetts, 1971). J-independent mutants were isolated as revertants of atraJ−mutant; they still carry thetraJ−mutation but also carry at least one other mutation which results in transfer in the absence of thetraJgene product. J-independent transfer of these mutants is not inhibited by the R 100 repressor. Various models are presented which can account for the properties oftraJ−mutants and of these J-independent revertants.
A multivariate analysis of subline divergence in the shape of the mandible in C57BL/Gr mice
Authors: Festing Michael
Published: September 2009

The shape of the mandible in. nine sublines of C57BL/Gr, seven other strains of ‘C57 ancestry’ and four unrelated strains was studied by multivariate techniques. The generalized distance function was used to classify individuals in the groups which they most closely resembled. The degree of misclassification depended on the pedigree relationship between strains and sublines. The generalized distance between pairs of subline centeroids was also highly correlated (r = 0·60) with the number of generations between them. A canonical variate analysis was used to reduce the dimensionality so that a graphical display of the relationships between strains and sublines could be made. The results agreed closely with the classification analysis. It was concluded that the shape of the mandible could be used for subline identification though the accuracy of this technique depends on how closely the sublines are related.
Non-homologous meiotic pairing in the A and B genomes of Brassica: its breeding significance in the production of variable amphidiploids
Authors: Prakash Shyam
Published: September 2009

Brassica juncea Coss (2n = 36) is a naturally occurring allotetraploid. In the progenies of F1 hybrids of its constituent parents B. campestris sub.sp. oleifera var. toria × B. nigra and B. campestris sub.sp. japonica × B. nigra, the majority of the plants were parthenogenetic homozygous amphidiploids like B. juncea whereas a few differed in morphological and physiological characteristics. The latter, presumed to have arisen partheno-genetically, were suspected to be homozygous for chromosomes changed by allosyndetic recombination. One of these derived plants with curley leaves was crossed first with one of the homozygous amphidiploids and secondly with B. c. sub.sp. oleifera var. toria. Sporocytes of the two hybrids were studied at meiosis. The presence of one or two quadrivalents in the first hybrid and two trivalents in the second suggested that allosyndetic recombination had occurred in the 18-chromosome hybrid. The progeny was presumed to have arisen through pseudo-diploid parthenogenesis and this in association with allosyndetic recombination may provide a means of breeding higher yielding genotypes.
Location of factors enhancing crossing over on linkage group I of Neurospora
Authors: Hargrave Jenny , Threlkeld S. F. H.
Published: September 2009

An enhancement of cross-over frequencies previously reported by Newcombe & Threlkeld (1972) is shown to be due to two regions located on linkage group I, a few cross-over units to the right of the centromere. The distal region appears to be shorter than the proximal region, but equally effective in enhancing cross-over frequencies. The longer proximal region is readily divisable by cross-overs and probably spans several crossover units.
Characterization of the F transfer cistron,traL
Authors: Willetts N. S.
Published: September 2009

The properties of two transfer-deficient Flacmutants (inEscherichia coliK12) carrying mutations in the cistrontraLare described. ThetraLproduct is needed for conjugational DNA transfer and for pilus formation, but not for surface exclusion; it is not plasmid-specific.traLmaps betweentraAandtraE; one of thetraLmutations is apparently polar ontraA. The properties of Tra+revertants of this mutation suggest that thetraLproduct is directly required for F-specific phage infection.
The effects of inhibition of protein synthesis on the phenotype ofAbnormal-abdomen
Authors: Hillman Ralph , Shafer Stephen J. , Sang James H.
Published: September 2009

Penetrance and expressivity of theDrosophilamutantAbnormal-abdomen(A53g) may be reduced by adding inhibitors of protein synthesis, of RNA synthesis, and of oxidative phosphorylation to the defined, sterile medium on which larvae are developing. When grown on regular diet, the mutant flies contain a higher concentration of total protein than do wild-type flies. The metabolic inhibitors which reduce the expressivity of the mutation also lower protein concentration in these mutant flies. The reduction of protein synthesis is directly correlated with the reduction of expression of the mutant genotype. The regulation of the morphological abdominal abnormalities by the complexA53ggenotype is discussed in relation to the control, by this same genetic system, of the mechanisms of protein synthesis.
Mixed self and random mating at two loci
Authors: Weir B. S. , Cockerham C. Clark
Published: September 2009

An infinite population practising a constant amount of selfing and random mating is studied. The effects of the mating system on two linked loci with an arbitrary number of neutral alleles are determined. Expressions are obtained for the two-locus descent measure, and hence genotypic frequencies and disequilibria functions, in any generation. The nature of the equilibrium population is deduced. The special cases of pure selfing or pure random mating and completely linked or completely unlinked loci are considered separately.
A new sex factor ofPseudomonas aeruginosa
Authors: Pemberton J. M. , Holloway B. W.
Published: September 2009

Of 150 wild-type strains ofPseudomonas aeruginosaexamined, 48 formed recombinants when mated toP. aeruginosastrain PAO FP−and hence presumably possess sex factors. Three different types of sex factor were distinguished by the pattern of transfer of particular markers in different regions of the chromosome and by the ability to confer resistance to mercury in strain PAO. One new sex factor, FP39, was studied in detail, and while similar to the previously studied FP2 in terms of transfer kinetics, natural stability and resistance to curing by acridines, it differed from FP2 in promoting chromosome transfer from a site 10 min to the left of the FP2 origin and in showing apparently aberrant entry kinetics for a leucine marker situated 48 min from the FP2 origin. This was due to FP39 having a genetic determinant either for a structural gene of leucine biosynthesis or a specific suppressor gene for this locus. PAO strains carrying both FP2 and FP39 were unstable for both sex factors, suggesting a relationship between them.
Gene symbols inAspergillus nidulans
Authors: Clutterbuck A. J.
Published: September 2009

Proposals are made for symbols consisting of a primary gene symbol of lower case italic letters referring to the mutant phenotype (three letters for new symbols, old symbols unchanged), an italic capital locus specific letter (or a hyphen in mutants not yet tested for allelism) and an italic mutant number. Optional superscripts are recommended to convey additional information. Further proposals relate to symbols for chromosome aberrations and to strain numbers.
Comparison of two transformation systems for the assay of theNeurosporaphotoreactivating enzyme
Authors: Tuveson R. W.
Published: September 2009

TheNeurospora crassaphotoreactivating enzyme has been assayed for by theHemophilus influenzaeandBacillus subtilistransformation systems. In contrast to theH. influenzaesystem, u.v.-treated transforming DNA fromB. subtilisdid not give evidence of reactivation of u.v. lesions by crude enzyme extracts fromN. crassawhen exposed to photoreactivating light. The u.v. dose required to inactivateB. subtilistransforming DNA is about ten times that required to inactivateH. influenzaeDNA to the same level of survival. This difference in dose required to inactivate DNA's of about the same base composition probably reflects the greater u.v. resistance of theB. subtilisrecipient strains used. Hypotheses are considered which suggest thatN. crassacrude enzyme extracts contain either nucleases which degradeB. subtilistransforming DNA excessively or an inhibitory factor which affects the transformation process itself.
Enzyme variability in theDrosophila willistoniGroup. V. Genic variation in natural populations ofDrosophila equinoxialis
Authors: Ayala Francisco J. , Powell Jeffrey R. , Tracey Martin L.
Published: September 2009

We have studied genetic variation at 27 loci in 42 samples from natural populations of a neotropical species,Drosophila equinoxialis, using standard techniques of starch-gel electrophoresis to detect allelic variation in genes coding for enzymes. There is considerarle genetic variability inD. equinoxialis. We have found allelic variation in each of the 27 loci, although not in every population. On the average, 71% of the loci are polymorphic – that is, the most common allele has a frequency no greater than 0·95 – in a given population. An individual is heterozygous on the average at 21·8% of its loci.

The amount of genetic variation fluctuates widely from locus to locus. At theMdh-2locus arout 1% of the individuals are heterozygotes; at the other extreme more than 56% of the individuals are heterozygous at theEst-3. At any given locus the configuration of allelic frequencies is strikingly similar from locality to locality. At each and every locus the same allele is generally the most common throughout the distribution of the species. Yet differences in gene frequencies occur between localities. The pattern of genetic variation is incompatible with the hypothesis that the variation is adaptively neutral. Genetic variation inD. equinoxialisis maintained by balancing natural selection.

The amount and pattern of genetic variation is similar inD. equinoxialisand its sibling species,D. willistoni. Yet the two species are genetically very different. Different sets of alleles occur at nearly 40% of the loci.
Experimental modification of the dominance relations of a melanotic tumour gene inDrosophila melanogaster
Authors: Belt Ann Louise , Burnet Barrie
Published: September 2009

The melanotic tumour genetu-C4inDrosophila melanogastershows incomplete dominance, together with variable penetrance and expressivity. It is tentatively located in the region of locus 52–53 on the third chromosome. Tumour formation in mutant homozygotes involves a precocious haemocyte transformation leading to the appearance of lamellocytes at the beginning of the third larval instar. These aggregate to form tumour-like masses which subsequently melanize. The process of tumour formation is in broad outline similar to that found in other tumour strains. Melanotic tumour formation is treated as a dichotomous threshold character, assuming an underlying normal distribution of liability relative to a fixed threshold. The expression of the tumour gene can be influenced by the levels of protein, phospholipid, nucleic acid and carbohydrate in the larval food medium, and changes in dominance and penetrance induced by sub-optimal environments deficient in these nutrients are positively correlated. Reinforcement by selection of the dominance relations oftu-C4was accompanied by correlated changes in penetrance. Conversely, selection for increased penetrance was accompanied by correlated changes in dominance. Dominance and penetrance, it is concluded, are fundamentally related aspects of tumour gene expression. Recruitment of dominance modifiers linked to the tumour gene was excluded by the mating scheme employed, and the observed changes in dominance relations in response to selection were due largely to modifiers located on the second chromosome. Changes in dominance relations produced by selection could be significantly reinforced, or reversed, by environmental factors and consequently show a substantial genotype – environment interaction effect. These facts are relevant to current theories of dominance evolution.
Chromosomal location of a prophage inPseudomonas aeruginosastrain PAO
Authors: Krishnapillai V. , Carey K. E.
Published: September 2009

Segregation of the prophage of bacteriophage 90 has been observed in reciprocal crosses between lysogenic and non-lysogenic parents ofPseudomonas aeruginosastrain PAO. Linkage of the prophage was shown to three genes determining histidine biosynthesis in that region of the chromosome 7–13 min from the site on the chromosome at which the sex factor FP2 promotes chromosome mobilization.
Enzyme protein polymorphism in the slug Arion ater
Authors: Burnet Barrie
Published: September 2009

Populations of the slug Arion ater rufus sampled from several localities in England and the Netherlands are polymorphic for different electro-phoretic variants of digestive-gland esterase and salivary-gland tetra-zolium oxidase. Samples of Arion ater ater, which is endemic to the British Isles, were found to be monomorphic for these enzymes. Localized populations of A. a. rufus in Britain could have originated from specimens imported accidentally from continental Europe. There is evidence for gene flow between overlapping populations of the two subspecies. In one of the English populations of A. a. rufus, studied in detail, polymorphism for esterase and tetrazolium oxidase is shown to be balanced. Heterosis may be an important factor contributing to the maintenance of balanced polymorphism for tetrazolium oxidase in this population.
Evidence of premeiotic control of chromosome pairing inTriticum aestivum
Authors: Bayliss M. W. , Riley Ralph
Published: September 2009

A genotype of wheat deficient for a pair of chromosomes stabilizing chiasma frequency against extremes of temperature was investigated to determine the position and duration of temperature sensitivity with respect to first metaphase of meiosis. Temperature changes over a critical range, followed by sequential sampling and measurement of chiasma frequency, showed a relatively short temperature-sensitive stage, the position and duration of which were dependent on the final temperature used. Comparison with meiotic timings made independently showed that the temperature-sensitive stage occurred in the premeiotic interphase. Euploid wheat was shown to have a stage in chiasma formation sensitive to high-temperature treatments at a similar time.

Comparison with the work of others showed that the sensitive stage lay between the last premeiotic mitosis and the start of DNA synthesis. This modification of chromosome pairing at a much earlier stage than has been previously demonstrated is further evidence that the processes of chromosome pairing and crossing-over are probably more complex than formerly envisaged.
Analysis of the resistance mediated by several R-factors to Tetracycline and Minocycline
Authors: Robertson J. M. , Reeve E. C. R.
Published: September 2009

The resistance levels conferred by the T-determinants in four R-factors to Tetracycline and Minocycline in cells ofEscherichia coliK 12, before and after induction of maximum resistance by treatment with sub-inhibitory concentrations of the drugs, are measured by simple growth-and-challenge tests. The effect of a plasmid TKwhich confers tetracycline resistance on its hostKlebsiella aerogenesis tested in the same way. The five T-determinants fall into a high-level and a low-level group for resistance, the former giving 3- to 4-fold higher resistance in both induced and uninduced cells than the latter. The T-determinants all confer much lower resistance to Minocycline (a tetracycline molecule modified at the C-6 and C-7 positions) than to Tetracycline. The main cause of this difference is that cells carrying a T-determinant exclude Minocycline much less efficiently than Tetracycline, but in addition Minocycline is less effective than Tetracycline in inducing increased resistance. These results are discussed in the light of a model put forward to explain the inducible nature of R-factor resistance to the tetracyclines.
A subvital gene inRana pipienslinked to the Burnsi locus
Authors: Browder Leon W.
Published: September 2009

A cross of a leopard frog heterozygous for the dominant Burnsi gene (B/ +) with a wild-type (+ / +) resulted in a large excess ofB/ + progeny. Two descendent lines established by theseB/ + progeny are characterized by excess +/ + progeny. These seemingly contradictory data are reconciled by postulating the existence of a dominant subvital gene (Sbv) linked to the + allele of Burnsi in the initial cross. Progeny used to establish subsequent lines were recombinants withSbvlinked toB. This proposed linkage would constitute the first case of linkage between two mutant loci in anuran amphibians.
Non-random association between electromorphs and inversion chromosomes in finite populations
Authors: Nei Masatoshi , Li Wen-Hsiung
Published: September 2009

With the aim of knowing the probable magnitude of non-random association between inversion chromosomes and electromorphs, both deterministic and stochastic studies are conducted on the evolutionary change of non-random association, which is defined as the difference in the frequency of a given allele between inversion and non-inversion chromosomes. In these studies inversion chromosomes are assumed to be subject to selection but electromorphs are selectively neutral, and recombination is allowed to occur between inversion and non-inversion chromosomes with a low frequency. The deterministic study has shown that in a variety of selective schemes for inversion chromosomes the non-random association decays at a rate equal to the recombination value in every generation. Thus, if the recombination value is of the order of 10−5˜ 10−4, it would take a long time for the non-random association to disappear. Furthermore, the stochastic study has indicated that random genetic drift generates non-random association of inversions and electromorphs in finite populations and the standard error of non-random association often becomes larger than the mean. In addition to these problems the time required for the electromorph frequencies in the inversion and noninversion chromosomes to become equal in a finite population and the probability that the population of inversion chromosomes remains monomorphic for the allele which existed in the initial inversion introduced are studied. Considering all these quantities, it is concluded that data on the non-random association between electromorphs and inversions are not very informative for the study of the maintenance of protein polymorphism. It is also indicated that in the study of association between electromorphs and inversion chromosomes non-random association or Yule's coefficient of association has a better property than the usual linkage disequilibrium measure or correlation coefficient. Implications of this study on some experimental observations are discussed.
Mitotic recombination inMusca domesticaL. and its influence on mosaicism, gynandromorphism and recombination in males
Authors: Rubini P. G. , Vecchi M. , Franco M. G.
Published: September 2009

In the housefly, mosaics appear spontaneously but rarely. Sexual mosaics or gynandromorphs also appear in strains in which sex determination is based on autosomal sex factors. Rare cases of recombination in the male have been reported by some authors. In field and laboratory populations, mitotic plates with figures indicating exchange of chromatid segments are regularly observed in tissues of individuals of both sexes and at all stages of development. All these anomalies are interpreted as outward manifestation of the same phenomenon: mitotic recombination. The cytological basis of mitotic recombination, its relative frequency, its influence on linkage and genetic variability are discussed.
Transduction of inositol-fermenting ability demonstrating phylogenetic relationships among strains ofSalmonella typhimurium
Authors: Old D. C. , Dawes P. F. H. , Barker Ruth M.
Published: September 2009

The production of Inl+recombinants was readily demonstrated in transductional crosses from Inl+donor strains to Inl−recipient strains from different biotypes and biogroups. None of numerous crosses between different pairs of strains from biotypes 25 and 26 and the biogroup FIRN (biotypes 29, 30, 31 and 32) gave Inl+recombinants suggesting that theinlmutation was present at the same intragenic site in all of these strains. Strains of the FIRN biogroup (Fim−Inl−Rha−Bxyl−) are thought to have descended by successiverhaandfimmutations from an ancestral bacterium of biotype 25 (Fim+Inl−Rha+Bxyl−). The sites of theinlmutations in other Inl−biotypes (9, 10, 27 and 25hi) were independent and each was different from that in strains from biotypes 25, 26 and FIRN.
Construction of isomitochondrial and isonuclear strains for recombinational analysis of mitochondrial loci in S. cerevisiae
Authors: Kruszewska A. , Szcześniak B.
Published: September 2009

In the mitochondrial and nuclear genetic background of the 777-3A strain (op1, ade1, α) a set of strains with different nutritional requirements and mating types, carrying the op1 mutation versus its wild-type OP1 allele was constructed. This makes possible the use of strains with the same genetic background in recombinational analysis of mitochondrial loci.
Effects ofY-chromosome variants on the male behaviour of the mouseMus musculus
Authors: Stewart A. D. , Manning Aubrey , Batty Jennifer
Published: September 2009

A study of crosses between CBA/FaCam and C57B1/6Fa mice revealed an effect of the origin of theY-chromosome on testis weight and aggressive behaviour, but failed to reveal any effect on sexual behaviour and androgen metabolism. There is therefore no evidence that androgens mediate theY-linked variation in aggressive behaviour and testis weight. On behavioural grounds, it is difficult to compare measures of sexual and aggressive behaviour, but it appears from these results that there are major genetic components on theY-chromosome controlling the development of sexual and aggressive behaviour which are distinct.
The genetic variability of polygenic characters under optimizing selection, mutation and drift
Authors: Bulmer M. G.
Published: September 2009

The effect of optimizing selection, mutation and drift on a metric character determined by a large number of loci with equal effects without dominance was investigated theoretically. Conditions for a stable equilibrium under selection and mutation, in the absence of drift, have been obtained, and hence the amount of genetic variability which can be maintained by mutation has been determined. An approximate expression for the average amount of genetic variability to be expected in the presence of drift in a population of finite size has also been obtained and evaluated.
Mutants inSaccharomyces lactiscontrolling both β-glucosidase and β-galactosidase activities
Authors: Tingle M. , Halvorson H. O.
Published: September 2009

InSaccharomyces lactis, a class of mutants isolated for low β-glucosidase activity are reduced in activity for β-galactosidase as well. Genetic studies indicate that their properties are the result of a single mutation in a nuclear gene. In diploide containing a wild-type and mutant β-galactosidase allele, the mutant phenotype is partially dominant. The two enzymes can be separated physically and under appropriate conditions are induced independently in wild-type strains.
Fixation probability of a mutant influenced by random fluctuation of selection intensity
Authors: Ohta Tomoko
Published: September 2009

The probability of fixation of a mutant gene in a finite population was investigated by taking into account the effect of random fluctuation of selection intensity. It was shown that not only the product of the effective population number and average selection coefficient (Nes) is important, but also the ratio of the mean and the variance of selection coefficient (s/Vs) has an important influence on fixation probability. In particular, when this ratio is small, a mutant gene, even if selected against, becomes fixed in the population like a selectively neutral mutant. In general, when random fluctuation of selection intensity is not negligible it may be convenient to use ‘effective selection coefficient’. The bearing of the present findings on the neutral mutation-random drift theory of evolution and variation at the molecular level was discussed.
Is subline differentiation a continuing process in inbred strains of mice?
Authors: Hoi-Sen Yong
Published: September 2009

Two new sublines of the C57BL/Gr strain of mice have been studied which were derived from earlier sublines in which no genetic variance could be demonstrated. The incidence of some 31 minor skeletal variants was examined which could thus go up or down. As new subline differences have arisen with about the same frequency and mean magnitude of effect as in the past, there is no doubt that, at least in the C57BL strain, subline differentiation is a continuing process. Its high frequency (about 0·01 changes per character at risk per generation) is difficult to reconcile with spontaneous mutation rates of single genes in the mouse. The possibility must thus be considered that some other self-perpetuating processes or entities of some degree of stability are handed down in the lines of descent in which they have arisen, or perhaps become unmasked. There is no reason to suppose that this type of event is confined to inbred strains (in which it can be demonstrated fairly easily); it presumably occurs similarly in mixed stocks in which it would scarcely be detectable.
The average number and the variance of generations at particular gene frequency in the course of fixation of a mutant gene in a finite population
Authors: Maruyama Takeo
Published: September 2009

In the case of an allele which is going to become fixed in a population, the average number of generations for which the population assumes particular gene frequencies is investigated, using the diffusion approximation. Explicit formulas were obtained and they were checked by computer simulations. As a particular case, it is shown that if a new mutant that is selectively neutral is eventually fixed in a population of sizeN, it spends two generations on average at each of the intermediate frequencies (1/2N, 2/2N, …, (2N−1)/2N), and the variance at each frequency is four generations.
Natural selection for enzyme variants among parthenogenetic Daphnia magna
Authors: Hebert P. D. N. , Ward R. D. , Gibson J. B.
Published: September 2009

The frequencies of genetically determined electrophoretic variants of two enzyme systems in the parthenogenetic crustacean D. magna have been followed in two isolated populations. In both populations a marked excess of hetero-zygotes was found in the later samples. It is concluded that the observed changes in gene and genotypic frequencies are due to natural selection as both migration and genetic drift can be excluded.
Sexuality in Neurospora crassa II. Genes affecting the sexual development cycle
Authors: Vigfusson N. V. , Weijer J.
Published: September 2009

Eighteen male sterile mutants of N. crassa which block various stages of the sexual development cycle have been functionally categorized on the basis of complementation tests. Nine of these (those which block early stages of the sexual cycle) have also been analysed through recombination studies. On the basis of these data, a minimum of four genes appear to be involved in early stages of sexual development (i.e. probably prior to karyogamy) and several genes are indicated which control later stages of the cycle. Complementation phases with respect to sexual development in heterothallic Ascomycetes are discussed as well as a comparison of results obtained with expectations and with those obtained in related Ascomycetes.
A comparative study of the coats of chimaeric mice and those of heterozygotes for X-linked genes
Authors: Cattanach B. M. , Wolfe H. G. , Lyon M. F.
Published: September 2009

The coats of Ta–Ta+ and c–c+ chimaeric mice have been compared with those of Ta heterozygotes and animals heterozygous for an X-autosome translocation which causes c-variegation. With one exception all those features typical of the heterozygotes were found in their chimaeric counterparts, thus showing that the creation of two cell populations by X-inactivation can ultimately lead to the observed heterozygous phenotypes. The one exceptional feature not found in c-variegated chimaeric mice was the progessive increase in the proportion of pigmented hairs in c areas with age which occurs in X-autosome translocation heterozygotes.

The coat of a Modp / + – Ta chimaeric animal was also investigated. Ta hairs showing only the colour effect of Modp were numerous, suggesting that Modp and Ta affect different cell populations. However, Ta hairs showing the structural effect of Modp were very rare. The two observations suggest Modp can operate independently upon two different cell types – melanocytes and hair follicle cells.
Multiple changes in lens protein composition associated with the CatFr gene in the mouse
Authors: Day T. H. , Clayton R. M.
Published: September 2009

The ocular cataracts produced by the dominant CatFr gene in the mouse, Mus musculus, are associated with quantitative changes in the lens proteins (crystallins). The three classes of crystallin are affected differentially in homozygotes. Heterozygotes show a smaller effect. The quantitative levels of crystallin subunits are also affected and these changes are different for each subunit. The overall loss in protein is not readily explicable hi terms of a generalised leakage or a general tendency to insolubilisation. Possible mechanisms for the action of the gene are suggested.
Chromosome mapping inPseudomonas aeruginosa
Authors: Pemberton J. M. , Holloway B. W.
Published: September 2009

A more extensive linkage map ofPseudomonas aeruginosastrain PAO has been compiled from data obtained by both, conjugation and transduction procedures. All the markers examined are located on one linkage group and the available evidence suggests that the sex factor FP2 promotes transfer of the chromosome in a polarized manner from only one site on this linkage group.
Studies of aromatic biosynthetic and catabolic enzymes inUstilago maydisand in mutants ofU. violacea
Authors: Berlyn Mary B. , Giles Norman H.
Published: September 2009

A multienzyme complex for five of the enzymes in the prechorismate portion of the aromatic biosynthetic pathway has been demonstrated inUstilago violacea, and has previously been reported inU. maydis(Ahmed & Giles, 1969). This complex is similar to that found inNeurospora crassaand other fungi. InU. violaceapolyaromatic-requiring mutants show pleiotropic deficiencies for all five of these enzymes, similar to the extreme pleiotropic polar mutants of thearomgene cluster in Neurospora (Giles, Case, Partridge & Ahmed, 1967a; Case & Giles, 1971). This result is interpreted as mutational evidence for anaromgene cluster inU. violaceacomparable to that inN. crassa. A second low molecular weight, heat-stable isozyme of dehydroquinase is shown to be present at high (constitutive) levels inU. maydis, as previously indicated by Ahmed & Giles (1969), but this activity is increased to extraordinarily high levels in cells grown in the presence of quinate. In contrast,U. violaceastrains do not grow on quinate, have a single, heat-labile dehydroquinase species, and lack activities for other enzymes in the quinate catabolic pathway.
Non-reciprocal intragenic mitotic recombination inDrosophila melanogaster
Authors: Kelly Patricia Tamarah
Published: September 2009

X-ray-induced mitotic recombination within the lozenge locus ofDrosophila melanogasterwas found to be non-reciprocal. Recombination was detected by the presence of faceted spots in a smooth (lozenge) eye. Markers were present so that if recombination were reciprocal, equal numbers of vermilion and apricot-vermilion-coloured faceted spots would be formed. Of 19 faceted spots found among more than 60000 eyes examined, 10 were vermilion, 7 variegated (some vermilion and some apricot-vermilion-coloured facets), and 2 probably variegated. None was uniformly apricot-vermilion in colour. Four mechanisms for the formation of faceted spots are discussed: double reciprocal recombination, misrepair or gene conversion before chromatid replication, misrepair or gene conversion after chromatid replication, and misrepair or gene conversion followed by chromosome loss. The evidence most strongly supports the hypothesis that all faceted spots were formed by either misrepair following X-irradiation or gene conversion and were originally vermilion in colour. Subsequent chromosome loss from these vermilion cells led to the production of variegated spots. Variegated spots were generally smaller than those uniformly vermilion in colour, indicating that chromosome loss may occur with greater frequency in older irradiated larvae.
Suppressors of ‘blue’ mutations in yeast
Authors: Mitchell I. de G. , Bevan E. A.
Published: September 2009

Mutants ofSaccharomyces cerevisiaewhose colonies were blue when grown on nutrient agar medium containing methylene blue reverted to wild-type with white-colony phenotype at high frequency. This reversion was controlled by nuclear gene suppressors in some mutants, and by cytoplasmic suppressors in others. Each of the latter suppressed several independetly segregating blue mutants. These suppressors could be divided into two classes: suppression by petite mutations which behaved as recessives, and suppression by a cytoplasmic factor in respiration-sufficient cells which behaved as dominant over wild-type but might also be a mutation ofrho. A relationship between blue mutation and temperature sensitivity was suggested.
A stable duplication as an intermediate in the selection of deletion mutants of phage T4
Authors: van de Vate C. , Symonds N.
Published: September 2009

A selective procedure is described for the isolation of deletions in phage T4. This is based on the properties of partial diploids which possess a tandem duplication covering the rII region. The starting-point of the procedure is a particular s1231/3157 diploid which has a high segregation frequency and so possesses a long duplication. The replacement in this diploid of the large deletion 3157 by the small one 196 further increases the length of this duplication and removes the terminal redundancy of the resulting phage which are then non-viable. New compensating deletions which restore the terminal redundancy and thus the viability to these diploids are thereby selected. Nine new independent T4 deletions have been isolated by this procedure. The length of three has been estimated by terminal redundancy measurements and each found to be appreciably longer than the rII region. While developing the isolation procedure a key diploid intermediate was identified with the property that is was completely stable; that is, unlike typical diploids which continually generate haploid segregants during phage multiplications, this diploid strain produced no viable haploid segregants. This unexpected finding led us to examine the general problem of how tandem duplications can be stabilized. The solution we propose here is a structural one involving new stabilizing deletions which penetrate into one arm of the duplication removing certain essential genes. These stabilizing deletions are located in such a way that all haploid segregants formed by recombination are necessarily non-viable. Further investigations of the original stable diploid, and others isolated subsequently, validated this model for these phage diploids. It also led to the recognition of several novel genetic structures involving repeated DNA sequences which, together with the concept of the stabilizing deletions, could be of general significance.
A simple and rapid technique for obtaining a high proportion of hybrid cleistothecia in Aspergillus nidulans
Authors: Bainbridge B. W.
Published: September 2009

A technique is reported for crossing strains of Aspergillus nidulans which produces hybrid cleistothecia in 7 days. The method depends on the partial inhibition of cleistothecium formation of auxotrophic mutants by growth-factor limitation. Cleistothecia form at the junction of two strains inoculated on to complete medium. The method has a number of advantages over standard techniques.