bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetical analysis of proline mutants and their suppressors inAspergillus nidulans
Authors: Weglenski P.
Published: September 2009

1.Complementation between thirteen proline auxotrophs inA. nidulanswas studied. Two groups of mutants with different complementation pattern were found. These two groups could also be distinguished on the basis of recombination tests.

2. The spontaneous reversion rate of proline mutants was established. In all cases studied the reversions were due to suppressor mutations. Dominant, semi-dominant and recessive suppressors were distinguished.

3. Complementation between recessive suppressors was studied. Only a few of the suppressors obtained could be located in different complementation groups.

4. Three suppressor loci were mapped, two of them,su-2andsu-6in chromosome III linked to thephen-2locus, respectively 22 and 26 map units distant, and the third in chromosome I, linked to thead-9locus (1·9 map units).su-2is a mutant at theSu-4 prolocus already identified by Forbes (1956).

5. The action of these suppressors is thought to consist in affecting the pathway of arginine synthesis by one of three mechanisms: (1) accumulation of an inter mediate (ornithine); (2) increased activity of ornithine δ-transaminase; and (3) a third, as yet, unclear process possibly involving feed-back regulation of arginine synthesis or the regulation of arginine breakdown to ornithine.
Studies on mitotic gene conversion inUstilago
Authors: Holliday Robin
Published: September 2009

In order to develop a system for the study of the mechanism of intragenic recombination inUstilago, mutants lacking nitrate reductase activity were isolated, and five alleles were combined in pairs in ten vegetative heteroallelic diploids. The diploids have the mutant phenotype, i.e. inability to utilize nitrate as sole source of nitrogen, but they will recombine to produce wild-type cells much more frequently than the back-mutation rates of haploids or homoallelic diploids. The spontaneous rate of recombination can be enormously increased by low doses of UV light, particularly if treatment is during the period of DNA synthesis in the mitotic cycle. By means of half-tetrad analysis it has been shown that this process of intragenic recombination, as in other fungi, is due to gene conversion rather than reciprocal exchange. It has also been shown that the frequency of UV-induced conversion under standard conditions gives a rough measure of the distance between two mutant sites, since it was possible to use these frequencies to make a linear fine structure map of the gene. These results are discussed in relation to a hybrid DNA model for gene conversion slightly modified from that previously suggested for meiotic recombination.
The limits to artificial selection for body weight in the mouse I. The Limits Attained in Earlier Experiments
Authors: Roberts R. C.
Published: September 2009

1. The results of some selection experiments for body weight in the mouse, conducted in the past in this laboratory, have been examined from the point of view of the limits ultimately reached.

2. The limits that are apparently attained do not necessarily remain stable over prolonged periods of time; two large lines showed marked decreases despite continued selection for high body weight.

3. Selection for high body weight reached a limit in the region of 30 g. at 6 weeks of age; small mice reached their limit at around 12 g.

4. The time taken to reach the limit may vary from ten to thirty generations, even for this one trait.

5. The total response for unidirectional selection was between two and six times the phenotypic standard deviation, or three to twelve times the additive genetic standard deviation.

6. Consideration of the half-life of the selection responses excluded the likelihood of the chance fixation of alleles unfavourable to the direction of selection.

7. The loci contributing to the response could each have an effect amounting to anything from one-half to one phenotypic standard deviation in the base population.

8. This indicated that up to twenty loci had contributed to the response.

9. The intensity of selection practised was close to the optimum for obtaining the maximum total response.

10. The rule of parsimony would indicate the exhaustion of the additive genetic variance as an adequate explanation of the limits attained.
The limits to artificial selection for body weight in the mouse II. The Genetic Nature of the Limits
Authors: Roberts R. C.
Published: September 2009

1. The effects of long-continued selection for body weight in two lines of mice, one large and one small, are described.

2. The large line showed a sharp increase in weight after remaining at an apparent limit for twenty generations. A rare combinational event is suggested as the most likely explanation.

3. Reversed and relaxed selection from the large line at the limit failed to yield any response. This indicates that effectively, the additive genetic variance in this line had been exhausted.

4. In contrast, the small line at the limit regressed slightly towards the base population when selection was relaxed. Reversed selection yielded a ready response until a new limit was apparently reached. Loci affecting body weight in this line had therefore not been fixed by selection.

5. Natural selection, operating on viability between conception and the time when the selection was made, appears to explain best the lack of fixation in the small line.

6. Attention is drawn to the necessity of more experimental work to elucidate the genetic nature of the limits to artificial selection.
The formation of Hfr strains inEscherichia coliK12
Authors: Broda Paul
Published: September 2009

The isolation and characterization of an isogenic series of twelve Hfr strains is described. From their points of origin it was concluded that the sex factor integrates at a limited number of sites on the bacterial chromosome. Although the nutritional requirements of these Hfr strains were similar to those of the parent F+strain, it was observed that one group had a markedly slower growth rate. The relevance of these observations to theories on the nature of F+fertility and on the formation of Hfr strains is discussed.
The general importance of disruptive selection (A comment on Waddington and Robertson's recent paper)
Authors: Thoday J. M.
Published: September 2009

In their recent paper, Waddington & Robertson (1966) discuss the general importance of disruptive selection and make various points that call for comment.

First, their statement that ‘It is most desirable that Thoday's results … should be repeated, with special attention to the strict virginity of the flies used, …’ appears to some readers as a scarcely veiled imputation that my experiments, especially that of Thoday & Gibson (1962), were executed without technical competence, though Waddington has informed me such imputation was not intended.
Small eyes—a new dominant eye mutant in the mouse
Authors: Roberts R. C.
Published: September 2009

A new mutant, Small eyes (symbol Sey), that reduces the size of the eye in the mouse, is described. It is dominant, and lethal when homozygous.
Influence of non-lethal doses of radiation on allelic recombination inChlamydomonas reinhardi
Authors: Lawrence C. W.
Published: September 2009

The influence on allelic recombination of non-lethal doses of gamma radiation delivered at different stages during meiosis has been determined and the data compared with previous results concerning gene recombination. Both kinds of recombination are influenced at only two, probably the same two, meiotic stages. During the first sensitive stage, probably in preleptotene, the frequency of allelic recombination is increased, but that of gene recombination decreased. The frequency of both is increased during the second sensitive stage, which is probably in pachytene.
An approach to the problem of whether clustering of functionally related genes occurs in higher organisms
Authors: Elston R. C. , Glassman Edward
Published: September 2009

A Statistical analysis of the genome of D. melanogaster indicates that functionally related genes tend to be found on a particular chromosome and, when their locations within a given chromosome are measured in terms of map units, show a tendency to cluster; this clustering within chromosomes, however, is completely accounted for by the known clustering of all genes within chromosomes. Thus the analysis does not reveal any obvious functional significance for the arrangement of the genes within the chromosomes of this organism.
The bar-properties, in particular glucosylation of deoxy-ribonucleic acid, in crosses of bacteriophages T2 and T4
Authors: de Groot B.
Published: September 2009

Analysis of the inheritance of the three bar-properties of bacteriophage T4: exclusion of T2 from the progeny of crosses, glucosylation of the hydroxymethylcytosine (HMC)moiety of the DNA according to T4, and plating with large plaques onE. coliK strains, was carried out by means of marker rescue from T4 by T2 onE. coliK (λh) as a selective indicator. Five of the strains isolated plated with large plaques on K (λh), but did not exclude T2 and showed T2 glucosylation; plating onE. coliK (λh) was found to segregate from the other two bar-properties. The sixth isolate showed, in addition to plating with large plaques on K, partial non-excludability by the parental T4 and T4 glucosylation of HMC. If partial non-excludability is the result of T4 glucosylation, the role of the additional glucose substitutions might be a protective effect on the DNA against the exclusion factor of T4. This proposal is supported by the analysis of the progeny from a single burst from a cross of T4 and T2. The following T2 genes were partially excluded: host-range, no exclusion of parental T2, sensitivity to ultraviolet, and limited plating efficiency onE. coliK (λh). The exclusion factor of T4 is not transmitted to all progeny and does not behave like a bar-property. Only resistance to exclusion and T4 glucosylation were transmitted to all twenty-seven progeny of the single burst. The elimination of sensitivity to exclusion and T2 glucosylation is explained by assuming that the recombinant class with the exclusion factor of T4 and T2 α-glucosylation will exclude itself and be suicidal upon infection of a new host. Exclusion and differential glucosylation are discussed with regard to restriction and modification, respectively.
Recombination within theYlocus inAscobolus immersus
Authors: Kruszewska A. , Gajewski W.
Published: September 2009

Mutants of theYlocus differed appreciably in their basic conversion frequencies (frequencies of conversion in one-point crosses) to wild type. The differences in the basic conversion frequencies in the opposite direction, i.e. from corresponding wild-type allele to mutant, were in general not pronounced. For some alleles frequencies of conversion in both directions were similar, but for the others they differed markedly. No evident correlation between the position of mutants on the map and their basic conversion frequencies was observed.

In two-point crosses in repulsion, the great majority of recombinant octads were of conversion type. In these crosses symmetry or asymmetry of conversion depended mainly on similarity or differences in basic conversion frequencies of mutants crossed. In crosses between mutants from different clusters the recombination frequencies were near to the sums of their basic conversion frequencies. Such ‘mutant specificity’ makes it impossible to establish the linear order of mutants on the basis of recombination frequencies in two-point crosses.

The results of two-point crosses in repulsion between mutants within clusters pointed to the influence of one allele on the frequency of conversion of another one. This ‘marker effect’ was also evident in some three-point crosses.

The frequencies of simultaneous conversions in two-point crosses in coupling did not show negative correlation with the distances between the mutants involved.

It seems that many of the data presented here are most easily explained by recently developed hybrid DNA models.
A genetic analysis of resistance to nystatin inSaccharomyces cerevisiae
Authors: Ahmed K. A. , Woods R. A.
Published: September 2009

1. A number of stable nystatin-resistant mutants of the yeastSaccharomyces cerevisiaehave been isolated from platings of a sensitive wild-type strain on low concentrations of the antibiotic.

2. These mutants were found to be resistant to 10, 15 or 60 units of drug/ml.

3. Analysis of meiotic segregants from crosses of these mutants to wild-type indicate that resistance is determined by two types of genes; resistance genes and modifiers.

4. Functional analysis of the mutants demonstrated the existence of three recessive resistance genes,nys-l,nys-2 andnys-3 and thatnys-1 andnys-2 were linked.

5. Genetic analysis showed thatnys-1 was affected by two modifiers,Mnys-1 andMnys-2, but that onlyMnys-2 affectednys-2 andnys-3.

6. The modifiersMnys-1 andMnys-2 are dominant.

7. An investigation of the effects of temperature and medium on resistance demonstrated marked interactions between genotype and environment for both the resistance genes and the modifiers.

8. Second-step mutants have been isolated by plating first-step mutants on higher concentrations of the drug. Some of these are resistant to 800 units/ml.

9. Some possible mechanisms of nystatin resistance are discussed.
The inheritance in wheat of crossability with rye
Authors: Riley Ralph , Chapman Victor
Published: September 2009

1. By the use of intervarietal chromosome substitution lines, the poor crossability with rye (S. cereale, 2n = 14) of the wheat (T. aestivum, 2n = 42) variety Hope was shown to be determined by chromosomes 5A and 5B. The genes Kr1 and Kr2, which are responsbile for poor crossability (Lein, 1943), are probably located on chromosomes 5B and 5A respectively.

2. Crossability is actively inhibited by the dominant alleles, Kr1 and Kr2, of Hope and is apparently not enhanced by the recessive alleles, kr1 and kr2, of the readily crossable variety Chinese Spring.

3. The inhibition of crossability with rye conferred evolutionary and agricultural advantage upon wheat by preventing the production of sterile wheat-rye hybrids which could be regarded as weeds generated from within the crop.
A genetic study of primary and secondary reversions of sometryptophanAauxotrophs ofSalmonella typhimurium
Authors: Riyasaty S. , Dawson G. W. P.
Published: September 2009

1. The linkage order of fourtryAmutants ofS. typhimurium, andcysB-12, is:

Attempts to plot the position oftryA-50were unsuccessful.

2. Some of the reversions oftryA-8,tryA-47,tryA-56andtryA-50were analysed genetically;tryA-52does not revert. All four auxotrophs gave reversions that were phenotypically and genetically indistinguishable from that expected by back-mutation of the original mutant site.

3. BothtryA-8andtryA-50produced reversions that grew as wild-type but were due to unlinked suppressor mutations. Some of these were super-suppressors in that they suppressed bothtryA-8andtryB-4; others suppressed many site mutants in thetryAgene but did not suppresstryB-4.

4. All the slow-growing reversions oftryA-8,tryA-50andtryA-56, and a minority of the semi-fast reversions oftryA-8, were due to unlinked suppressors.

5. All the slow-growing reversions oftryA-47, the semi-fast reversions oftryA-56and the majority of the semi-fast reversions oftryA-8were due to genetic changes that were inseparable, in very extensive experiments, from their original mutant site.

6. Slow-growing reversions oftryA-47produced faster growing mutants. Some of these were due to mutation in unlinked modifying genes and in others the genetic change was within thetryAgene. Nine of the latter had the genetic change just to the left of the47Ssite; in one the change was inseparable from the47Ssite. None had this further change to the right of the47Ssite. These further changes, in the absence of the47Ssite, gave prototrophic phenotypes; they are inter-site suppressors.
Four new linkage groups inCoprinus lagopus
Authors: Moore David
Published: September 2009

1. By means of tetrad analysis three vitamin-requiring mutants have been established as markers of centromeres distinct from those of the two known chromosomes.

2. Mutants existing in stock were tested for linkage with these centromere markers, and four previously unknown linkage groups with independent centromeres thereby established and accurately mapped.

3. Corrections were made to the maps of existing linkage groups. TheAlocus (Group I) was shown to be approximately four times as distant from its centromere as hitherto supposed (at least in most crosses); and several markers of Group II were mapped for the first time.
Sex pili and common pili in the conjugational transfer of colicin factor Ib bySalmonella typhimurium
Authors: Meynell G. G. , Lawn A. M.
Published: September 2009

The kinetics of spread of colicin factor Ib (colIb) incol− cultures ofS. typhimuriumwas studied. The rate of spread was greater withpil+ strains (those forming common pili) than withpil− strains. The difference reflects inefficient pairing betweenpil− cells, which donate or receivecolIbefficiently only when mated withpil+ cells. The donor function ofcolIbis known to be repressed a few generations after it is acquired by acol− cell. While donor ability is manifest, a new type of pilus (the ‘Ib pilus’) is formed which is morphologically distinct from common pili and other sex pili such as that determined by the F factor. The Ib pilus is presumably involved in the transfer ofcolIbby conjugation.
Some additional results on the maintenance of kappa particles inParamecium aurelia(stock 51) after loss of the geneK
Authors: Beale G. H. , McPhail Sheila
Published: September 2009

Additional data are presented on the maintenance of kappa particles in cells ofP. aurelia(stock 51) after removal of the geneK. It is shown that kappa particles may be maintained for as long as twenty-seven fissions in the absence ofK, or may disappear before eight fissions. Slight retardation in fission rate of paramecia quickly eliminates kappa particles. The bearing of these results on the metagon theory is discussed.
On the induction of a recombination-deficient mutant ofEscherichia coliK-12
Authors: Ben-Gurion Renana
Published: September 2009

A lysogenic, recombination-deficient bacterial mutant (rec−) can be induced to produce λind−C587 by a temperature shift, although it does not produce phage after u.v. irradiation when lysogenic for wild λ. When this mutant (rec−) was made colicinogenic for colicins E2 and I, colicin production was found not to be inducible.

Superinfection of irradiated lysogenicrec−(λ) bacteria, at doses of irradiation that did not reduce their capacity to produce phage λ, was not productive. It seems therefore that a certain product(s) that usually arises following u.v. irradiation inrec+cells, and triggers the induction of lysogenic and colicinogenic cells by causing loss of immunity or repression, is not produced in therec−mutant. However, immunity is lost and the prophage is induced after a temperature shift inrec−cells which are lysogenic for λind−C857.
Polarized exclusion of bacteriophage T2 in crosses with T4
Authors: De Groot B.
Published: September 2009

Four crosses were made between bacteriophages T4 and partially non-excludable T2exr+4. Each cross was designed as a four-factor cross: in total seven pairs of homologous genes were used as markers, extending over half the circular map from the locus for adsorption specificity (h+) along the map segment for the early functions to osmotic-shock sensitivity (o).

The frequencies of T2 markers recovered in the progeny show polarized exclusion: the frequencies are low forh+2at the beginning of the map segment for the early functions and increasing too+2. Recombination of T2exr+4is restricted for all loci concerned and the recombinational events are probably non-reciprocal. Restriction of sequential replication from a fixed starting point is proposed to explain polarized exclusion of T2 genes. Non-homology is dicussed in relation to restricted recombination.
Homoeologous pairing of a chromosome from Agropyron elongatum with those of Triticum aestivum and Aegilops speltoides
Authors: Johnson Roy , Kimber Gordon
Published: September 2009

1. Complex hybrids were produced having twenty-nine chromosomes, consisting of one telocentric and twenty complete chromosomes of T. aestivum (2n = 6x = 42), seven complete chromosomes of Ae. speltoides (2n = 2x = 14) and one telocentric chromosome derived from A. elongatum (2n = 10x = 70). The presence of the Ae. speltoides genome permitted pairing between homoeologous chromosomes at meiosis and the behaviour of the two telocentric chromosomes was observed.

2. The A. elongatum chromosome was seen to pair with chromosomes homoeologous to those of group 6. There was no evidence that it paired with chromosomes of any other group.

3. When the A. elongatum telocentric and those of 6A and 6D occurred in the same configuration it was evident that the telocentrics 6A and 6D were for corresponding chromosome arms, and the A. elongatum telocentric for the opposite arm.

4. The average rate of pairing was much lower for the A. elongatum telocentric than for wheat telocentrics. Previous studies had indicated very good genetic compensation of the A. elongatum chromosome for chromosomes 6A and 6D. It was therefore indicated that genetic equivalence and pairing affinity were not closely related in this case. Some implications of this are discussed.
A partial deletion map of the galactose operon inE. coliK12
Authors: Davison John , Frame Robin , Bishop John
Published: September 2009

We have isolated a number of λdgHFT lysates which carry proximal fragments of the galactose operon. Most of these have been shown to be different, and each terminates in either the kinase or transferase cistron. They divide the kinase cistron genetically into seven blocks of mutants, and the transferase into eight.

When a λdgis used to transduce a bacterium which carries a mutation in a cistron which is intact in the λdgthe transduction frequency is high in the presence of λ-helper. This is attributed to integration of the transducing fragment at the λ-attachment site and complementation between the two operons in the heterogenote. When the same λdgtransduces a mutation lying in the cistron in which the λdgterminates, so that recombination within the galactose operon is obligatory, the transduction frequency is 10 to 1000 times less.

In such cases there is a general increase in transduction frequency between distal mutations (i.e. those lying near the termination of the deletion) and proximal mutations, but the relationship does not hold for many individual pairs of mutants, probably due to physiological differences between the bacterial strains.
Nijmegen waltzer—a new neurological mutant in the mouse
Authors: van Abeelen J. H. F. , van der Kroon P. H. W.
Published: September 2009

A new neurological mouse mutant, Nijmegen waltzer (symbol nv), that causes circling and head-shaking without deafness, a marked tendency for aggressiveness, and reduced weight, is described. It is a single autosomal recessive, with complete penetrance and variable expression, and is probably located in linkage group I.
A study on simultaneous conversions in linked genes inAscobolus immersus
Authors: Paszewski Andrzej
Published: September 2009

White-spored mutants ofA. immersuswere used in experiments carried out to study the relationship between conversions occurring simultaneously in linked genes, and to check whether conversion occurs at random in the two chromatids of a chromosome.

Conversions in two loosely linked loci were shown to be independent of each other and randomly distributed between sister chromatids. On the other hand, conversions in two closely linked loci showed a high correlation of occurrence.
On the relationship between heterochromatization and variegation inDrosophila, with special reference to temperature sensitive periods
Authors: Hartmann-Goldstein Ingeborg J.
Published: September 2009

Using a strain ofD. melanogastercarrying an X-4 translocation, comparison between groups of individuals cultured at 14°, 19° and 25°C. showed good correlation between heterochromatization, variegation in malpighian tubules andNotch. All these phenomena are enhanced by low temperatures. Correlation was less good within each temperature group, and considerable variability was observed between individuals within the group, and between nuclei from one individual.

Experiments involving a temperature change during the embryonic period indicate that (1) heterochromatization is especially temperature-sensitive during the early embryonic period but may be increased by low temperature later, (2) larval malpighian tubules are sensitive to temperature only during the early embryonic stage, and (3)Nis influenced by temperature during early embryonic life and also during the larval period.

Our observations, in conjunction with those of other workers, could be explained as follows: exposure of individuals to low temperature at a time when a specific system is beginning to differentiate will cause the processes concerned to be blocked in some cells. At least during the early embryonic stages this appears to involve heterochromatization of the relevant locus. Once the processes are established which will lead to the formation of a character, further heterochromatization has no effect on the phenotype. Temperature may affect pupal or adult phenotype in this way or by a direct action on the metabolic processes of cells.

Further experiments showed: (1) the greatest temperature-sensitivity of all three phenomena within the first 6 hours of embryonic life; (2) striking fluctuations of the effect of temperature, especially within the early embryonic period; (3) close correspondence between all three phenomena in time of response to temperature. Some alternative interpretations are considered.
The initiation and development of the hair follicle population in tabby mice
Authors: Claxton J. H.
Published: September 2009

Hair follicle initiation and development was examined in tabby mutants and compared with a previous study of this sequence in normal mice. Initiation commenced at about the 17th embryonic day and continued for 1 and possibly 2 days after birth. Although central primary follicle initiation was of shorter than normal duration, it was more rapid, with the result that the central primaries achieved a greater maximum density, and their total numbers were greater in tabby than in normal mice.

In general structural terms, follicle group development proceeded normally except that no secondary follicles appeared, and for this reason, the mature grouping pattern of follicles was comparatively simple. Central primary follicles, the first to be initiated, were evenly spaced in the skin but the later association of lateral primaries with them was unusually close, and the resulting groups of primary follicles were relatively more compact in the mutants than they were in normal mice.

No simple explanation in terms of the altered timing of follicle initiation or the reduced complexity of the follicle group could be given for the abnormalities of the tabby coat.

Selection for high and low numbers of secondary vibrissae in tabby mice produced some correlated changes in the maincoat follicle population, but there was no apparent alteration to the time of onset of initiation. Evidently selection did not simply modify the effects of theTagene.
Genetic studies on mutations in species A and B of theAnopheles gambiaecomplex
Authors: Mason G. F.
Published: September 2009

1. A number of mutants affecting changes in the pigment of larval and adultAn. gambiaeare reported.

2. Two other pigment characters are also described. One of these, diamond, is probably inherited as a single factor.

3. Two of the mutants are sex-linked and the experimental results showAn. gambiaeto have aDrosophilaform of sex-linkage.

4. The sex-linked white-eye mutant is shown to be epistatic to the gene for collar and the characters diamond and red stripe.

5. Attention is drawn to the difference in sex-linkage betweenAn. gambiae, andC. pipiensandAe. aegyptiwhich may indicate different methods of sex-determination.
Penetrance of a rare genetic defect
Authors: Sittmann K.
Published: September 2009

Contrary to the conclusion of earlier workers, penetrance of a very rare genetic defect, congenital tremor in White Leghorn chicks, was found to be complete. By appropriate correction of the original data for small family size it is shown that the defect is determined not by one but two pairs of autosomal recessive genes. In the terminology of human genetics, ascertainment of affected individuals corresponded to conditions of ‘truncate’ selection in the case of maternal sibships and more nearly to ‘single’ selection in the case of paternal sibships.
The recognition of an alien chromosome segment translocated to a wheat chromosome
Authors: Kimber G.
Published: September 2009

1. Chromosome 6B of T. aestivum, to which a small segment of an Ae. umbellulata chromosome had been translocated, was examined both by interference microscopy and in stained preparations.

2. In the stained preparation a constriction was observed in the long arm of chromosome 6B and also a terminal knob that was also observed on chromosome A of Ae. umbellulata.

3. These features were also observed by interference microscopy and in addition the portion of the chromosome 6B of Transfer distal to the constriction had different phase-retarding properties.

4. It is concluded that the part of chromosome 6B distal to the constriction is the part of Ae. umbellulata chromosome A which carries the gene for the leaf-rust resistance of that species and of the wheat variety into which it was translocated.
Developmental ‘Noise‘ and a congenital malformation
Authors: Adams Morton S. , Niswander Jerry D.
Published: September 2009

Non-directional asymmetry of paired organs is attributed to developmental ‘noise’. The level of asymmetry is inversely correlated to the degree of developmental stability. Children affected with familial cleft lip ± cleft palate have an increased asymmetry of their dermatoglyphics and molar teeth. The action of polygenes with a quasi-continuous distribution is consistent with this observation.
The sex factor of colicin factor E1a
Authors: Meynell G. G. , Lawn A. M.
Published: September 2009

The sex factor ofcolE1aappears related to Ib, the sex factor ofcolIb, by each of three criteria: mutual inhibition of epidemic spread, antigenic structure of the sex pilus and susceptibility to I phage. The failure of each factor to spread in cultures carrying the other implies that donor ability is subject to a cytoplasmic repressor. Unlike twocolIfactors,colE1aandcolIa(orIb) can co-exist to give a doubly colicinogenic strain.
Mapping ofochresuppressors inEscherichia coli
Authors: Eggertsson Gudmundur
Published: September 2009

Genetic mapping of suppressors of theilv-188mutation is described. Suppressors of this mutation have been mapped at fourochresuppressor loci:sup L,sup M,sup Nandsup O. Theochresuppressor described by Brenner & Beckwith is shown not to suppressilv-188whereas thesuppressor described by the same authors suppressesilv-188and may represent the same locus assupOsuppressors. The mapping by P1 transduction of thesup L,sup Mandsup Nloci is described.
Genetic studies inEudorina
Authors: Mishra Nawin C. , Threlkeld S. F. H.
Published: September 2009

A formal genetic analysis of the heterothallic, colonial green algaEudorina eleganshas been described. Wild-type strains were found to be sensitive to different drugs when grown on minimal agar containing very low concentrations of these drugs. Mutant strains resistant to high concentrations of drugs have been isolated. These aremsr-500(resistant to 500 μg/ml of DL-methionine-DL-sulfoximine),ery-r-100(resistant to 100 μg/ml of erythromycin) andsr-100(resistant to 100 μg/ml of streptomycin). The wild-type phenotypes sensitive to these drugs have been designated asmss-500,ery-s-100andss-100respectively. Thesr-100also showed cross-resistance to other antibiotics belonging to the streptomycin group.

On genetic analysis, themsr-500andery-s-100were found to be inherited in a Mendelian way. These alleles are not linked to each other or to the mating type locus. The inheritance of mating type was found to be due to a single gene difference.

The inheritance ofss-100/sr-100was found to be non-chromosomal and was characteristically uniparental, always transmitted through the female parent. The evidence for the non-chromosomal gene (NC genes) controllingsr-100/ss-100phenotypes in this organism has been derived from the exceptional zygotes in which the male parent apparently transmits streptomycin resistance to the progeny. Although ultraviolet or gamma-radiation resulted in normal survival curves of the exposed cells, no mutant deficient in any nutritional requirement was isolated.
Inhibition of mitochondrial synthesis in yeast by erythromycin: cytoplasmic and nuclear factors controlling resistance
Authors: Thomas D. Y. , Wilkie D.
Published: September 2009

Erythromycin-resistant mutants were separated into two categories showing Mendelian and non-Mendelian inheritance of resistance respectively. The cytoplasmic factor was located in the mitochondrion based on the fact that the loss of the mitochondrial genetic unit associated with the petite mutation (the ρ factor, assumed to be the mitochondrial DNA) resulted in a corresponding permanent loss of resistance. Conversely, the petite mutation in gene resistant mutants had no effect on the inheritance of resistance.

Analysis of vegetative and sexual progeny of isolated zygotes from a number of crosses between resistant and sensitive strains indicated that different mitochondrial types, both sensitive and resistant, co-exist in the yeast cell and are distributed at random among daughter cells under non-selective conditions. Only resistant mitochondria are in evidence if zygotes are put down to proliferate on medium containing the antibiotic.

Resistant strains were tested for retention of resistance following anaerobic culture (known to cause disruption of mitochondria). The cytoplasmic mutants retained their resistance but two gene-resistant mutants tested both lost their resistance. It was suggested in the latter case that resistance is dependent on the existence of intact mitochondrial membrane (possibly inner membrane). In the former mutants the mechanism of resistance may be the alteration of one or other of the components of the protein-synthesizing system of the organelle.
The effects of nutritional deficiencies on themaroon-likematernal effect in Drosophila
Authors: Chovnick A. , Sang J. H.
Published: September 2009

1. Themaroon-likematernal effect, present whenma-lflies are bred from non-mutant mothers, is not found among the late emergents from normal cultures. The hypothesis that this is due to a deficiency of some nutrient(s) in old cultures is tested by growing larvae on defined, germ-free media with the nutrients reduced one at a time.

2. Omission of lecithin (but not reduction of casein, sucrose, RNA or cholesterol) decreases the percentage of maternally affected emergents, in proportion to the lowering of the lecithin supply. This is not a consequence of choline deficiency but of the shortage of fatty acids. Oleic, palmitic and linoleic acids can substitute for lecithin, when adequate choline is provided.

3. Pantothenic acid, nicotinic acid, thiamine and biotin deficiencies (but not reduced pyridoxine, riboflavine or folic acid) also lower the proportion of maternally affected flies. There is an interaction between pantothenic acid and lecithin, but not between lecithin and the other effective vitamin deficiencies.

4. Addition of the excretory product hypoxanthine to the complete diet significantly lowers the proportion of maternally affected emergents, but equivalent amounts of uric acid, or of guanylic acid, do not. It is argued that the quantitive relationships make it improbable that accumulation of excretory products play any great part in the disappearance of the maternal effect, whereas it is more likely that nutritional deficiencies do.

5.ma-llarvae grown on low lecithin have the same complement of xanthine dehydrogenase as those reared on normal lecithin. The lecithin effect is therefore assumed to operate by affecting the pattern of pteridine synthesis. Phenylalanine, which would also be expected to alter this pattern, modifies the maternal effect similarly.
The production and characteristics of diploids inUstilago violacea
Authors: Day A. W. , Jones J. K.
Published: September 2009

1. Forty-nine auxotrophic mutants were isolated after irradiation with ultraviolet light. The biochemical requirements were identified and the response to possible precursors tested in some of them.

2. Diploid colonies were synthesized from compatible, auxotrophic haploid strains on an artificial medium by an adaptation of the balanced heterokaryon technique. Selection of diploid cells was especially convenient as the dikaryon cannot grow on such media, and is therefore only a transitory stage under these cultural conditions. Diploid cells were different in shape and size from haploids, and gave rise to colonies which could be distinguished by eye from haploids. The way in which diploid colonies arose from fusions between haploid cells was followed by microscopic observation. When known numbers of fused haploid cells were plated on minimal medium, diploid colonies occurred at a frequency of 3 × 10−4.

3. Diploid cells, heterozygous for mating-type alleles, were incompatible with either haploid mating-type (i.e. neutral).

4. Diploid cells could infect the host plant as a pure culture (i.e. they are solopathogenic).

5. Meiotic and mitotic segregation of the large-celled strains was used to confirm diploidy. Spontaneous mitotic segregation was very rare. Mitotic crossing-over was induced at a high frequency by irradiation of diploid cells with ultraviolet light. A convenient technique for induced haploidization was devised usingp-fluoro-phenylalanine. Preliminary evidence using this technique indicates a haploid chromosome number of at least seven.

6. It is considered thatU. violaceahas many advantages as an organism for genetical research, especially for analysis of the parasexual cycle.
Spontaneous transformation inBacillus subtilis
Authors: Ephrati-Elizur Erela
Published: September 2009

Cultures ofBacillus subtilisrelease transforming DNA during the early exponential and stationary phases of growth. The pattern of release of transforming DNA was followed by measuring transformation in a system consisting of a non-transformable DNA donor and a differently marked transformable recipient. Transformation in this system seems to be at least as efficient as that induced by purified DNA. Fluorescence microscopy revealed that released DNA remained bound extracellular to intact cells. The release of DNA during early exponential growth seemed to be correlated with the cells' proneness to lysis; both DNA release and cell lysis were inhibited by chloramphenicol. In stationary cells, the release of DNA was neither correlated with a similar proneness to lysis nor inhibited by chloramphenicol.
Dosage compensation as a developmental phenomenon inDrosophila
Authors: Lee Geoffrey L.
Published: September 2009

The three theories of dosage compensation inDrosophilaare examined. Data are presented supporting a developmental interpretation. The reason why such a mechanism is applicable in insects but not in mammals is discussed.
Frequency dependence of mating success inDrosophila pseudoobscura
Authors: Ehrman Lee
Published: September 2009

Matings ofDrosophila pseudoobscurawere observed in Elens-Wattiaux chambers, using individuals of three karyotypes: AR/AR, AR/CH and CH/CH. In each chamber two karyotypes were represented, with frequencies 10:10, 2:18 or 18:2. The males of the heterokaryotype AR/CH tend to have an advantage in mating compared to the homokaryotypes, provided that both kinds of males are equally frequent, i.e. the ratio 10:10. This advantage is further increased when the heterokaryotype is a minority, the ratio 2:18. When the homokaryotype, AR/AR or CH/CH, is a minority (18:2) it is equally or more successful than the heterokaryotype in securing mates. Among females, the mating success is independent of frequency, or the minority females have sometimes only a slight advantage.
Chromosomal and extrachromosomal transmission of cellular melanization in the Freckled phenotype in Drosophila melanogaster
Authors: Barigozzi C. , Gorla M. Sari
Published: September 2009

Freckled (Frd) is a dominant mutant of D. melanogaster, lethal in double dose, which manifests itself by melanization in the adult stage, while nothing can be noticed in the larva and/or in the pupa. Its localization has been determined at nearly 102 of the second chromosome.

Among the offspring from backcrosses involving Frd, some individuals that do not carry the Frd gene exhibit a weak Frd manifestation in the adult stage, or a stronger one, mostly lethal, in the larval or pupal stage. Weak Frd, indicated as [Frd], is transmitted indefinitely without any recognizable linkage with the chromosomes, although its frequency is influenced by the 1st and, probably, by the 3rd chromosome. No matroclinous transmission has been found. It is concluded that [Frd] is probably controlled by an extrachromosomal entity, not located in the cytoplasm. The possible relationships between Frd and [Frd] are discussed.
Demonstration of different mutational sites controlling rhamnose fermentation in FIRN and non-FIRN rha−strains ofSalmonella typhimurium: an essay in bacterial archaeology
Authors: Morgenroth A. , Duguid J. P.
Published: September 2009

Observations of mutation and phage-mediated transduction of rhamnose-fermentation properties were made on two groups of wild-type rhamnose-non-fermenting (rha−) strains ofSalmonella typhimuriumisolated in several different countries. The ‘FIRN’ group included twenty-three strains in the biotypes 15, 16, 17 and 18, and the ‘non-FIRN rha−’ group included fourteen strains in a new biotype, provisionally designated 19 X d. The two groups showed different patterns of mutational behaviour and the pattern was uniform for the different strains in each group. Non-FIRN rha−strains gave rise directly to colonies of rha+mutant bacteria in platings on rhamnose minimal media. FIRN strains were unable to do this, but produced rha+bacteria by two successive mutations, the first of which yielded weakly fermenting (rhaw) bacteria capable of fermenting rhamnose in peptone water, but not of utilizing it for growth on minimal medium.

Rha+recombinant bacteria were produced in transductional crosses between any one FIRN strain and any one non-FIRN rha−strain, but not in any cross between one FIRN strain and another FIRN strain or between one non-FIRN rha−strain and another non-FIRN rha−strain. These findings suggest that although the sites of the rha−mutations are different between the FIRN and non-FIRN rha−groups, they are located at identical sites on the chromosome in all strains in either group. It is concluded that all FIRN strains have probably descended from a single ancestral strain which underwent mutations at two sites in the rhamnose region of the chromosome and that all non-FIRN rha−strains have descended from a single ancestral bacterium which underwent a mutation at a third site in the rhamnose region.
Selection under assortative mating in mice
Authors: Sutherland T. M. , Biondini Patricia E. , Haverland L. H.
Published: September 2009

1. Approximately 25000 mice have been produced over twelve generations of selection in nine lines. The experimental design involved a 3 × 3 factorial arrangement of direction of selection with mating system. The primary character measured was 6-week body weight.

2. Consistently high phenotypic correlations between mates have been achieved, positive in the assortative lines, negative in the disassortative lines. Correlations were low and inconsistent in direction in the random-bred lines. These correlations have had very little, if any, effect in redistributing the genetic variance as estimated from the variance component analysis; the expected higher variances in the assortative lines and expected lower variances in the disassortative lines have not appeared, thus leaving heritability unaffected.

3. Selection differentials likewise show no consistent advantage for the assortative lines, so that the progress from selection has been virtually identical in all three mating systems in each direction.

4. Assortment of mates, either positively or negatively, for characters of even moderate heritability appears to have little influence on the outcome of selection. On the other hand, selection has been singularly effective in modifying the mean 6-week weight, with progress markedly greater in the downward direction; indeed it appears that the lower limit, may already have been approximately attained.

5. Environmental effects operating in the various generations have affected all lines in remarkably consistent fashion.
Triplications and the problem of non-homologous crossing-over
Authors: Slizynska H.
Published: September 2009

Two triplications induced in a normal halpoid chromosome complement by TEM (Tr-I) and by mustard gas (Tr-II) are described. Two models which may lead by successive steps to the formation of a triplication are suggested. The induction of two latent breaks is essential in both of them. The origin of repeats in general is discussed. It is concluded that chromosome breaks rather than non-homologous crossing-over constitute the major source of repeats.
Analysis of quantitative inheritance of body size in mice: V. Effects of small numbers of polygenes on similar genetic backgrounds
Authors: Chai C. K.
Published: September 2009

Sublines carrying isolated polygenes determining body size, developed by selection and repeated backcrossing to theLGandSMstrains of mice, were inbred by full-sib matings with concomitant selection to study the inheritance of body size, using birth, weaning (28-day) and 60-day body weights as indices.

Mean body weights in those sublines backcrossed toSMand selected for large body size were greater than in those selected for small body size, proving that the difference resulting from seven earlier generations of backcrossing and selection, although small, was genetic and could be fixed by inbreeding. The mean body weights of the sublines selected for small body size drifted upward despite downward selection, a phenomenon thought to be due to the pressure of natural selection outweighing that of artificial selection.

In the sublines developed from backcrosses to theLGstrain, mice from lines selected for small body size attained a mean body weight greater than that of mice from lines selected for large body size and also than of the parentalLGstrain. These results were contrary to expectation and a genetic interpretation was offered.
The genetics ofDacus oleae: II. The genetics of two adult esterases
Authors: Zouros E. , Tsakas S. , Krimbas C. B.
Published: September 2009

The genetics of two esterase systems in adults of the olive fruit flyDacus oleae(Gmel.) have been studied by starch gel electrophoresis. Two unlinked autosomal genes, each with multiple alleles, control the synthesis of a number of isozymes. GeneAcontrols the synthesis of an acetylcholinesterase, and geneBthat of a pseudocholinesterase or lipase. GeneBproduces hybrid enzyme in heterozygotes for active alleles. In crosses the segregation of seven active and one silent allele in geneA, and of six active and one silent allele in geneB, have been studied. Six more active alleles for geneAand five active alleles of geneBhave not been studied in this paper.
Investigation of the mating system ofPseudomonas aeruginosastrain 1: I. Kinetic studies
Authors: Loutit J. S. , Pearce L. E. , Marinus M. G.
Published: September 2009

A method has been developed which will permit the mapping of the genetic material ofPseudomonas aeruginosa. This has been made possible by the use of potassium nitrate in the mating medium and other modifications which have increased the frequency of recombination. In certain circumstances, theilvA12marker may be transferred by more than 1% of the donor cells.