bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetic variability maintained in a finite population due to mutational production of neutral and nearly neutral isoalleles
Authors: Kimura Motoo
Published: September 2009

1. The average and the effective numbers of alleles maintained in a finite population due to mutational production of neutral isoalleles were studied by mathematical analysis and computer simulation.

2. The exact formula was derived for the effective number (ne) of alleles maintained in a population of effective sizeNe, assuming that there areKpossible allelic states and mutation occurs with equal frequency in all directions. If the number of allelic states is so large that every mutation is to a new, not pre-existing, allele, we havene= 4Neu+1 − 2Neu2, whereuis the mutation rate. Thus, the approximation formula,ne= 4Neu+1, given by Kimura & Crow (1964) is valid as long as 2Neu2≪ 1.

3. The formula for the average number of alleles (na) maintained in a population of actual sizeNand effective sizeNewas derived by using the method of diffusion approximation. If every mutation is to a new, not pre-existing, allele, we obtain

whereM= 4Neu. The average number of alleles as a function ofMandNis listed in Table 1.

4. In order to check the validity of the diffusion approximations, Monte Carlo experiments were carried out using the computer IBM 7090. The experiments showed that the approximations are satisfactory for practical purposes.

5. It is estimated that among the mutations produced by DNA base substitutions, synonymous mutations, that is, those which cause no alterations of amino acids, amount roughly to 0·2–0·3 in vertebrates.Incompletely synonymous mutations, that is, those which lead to substitution of chemically similar amino acids at a different position of the polypeptide chain from the active site and therefore produce almost no phenotypic effects, must be very common. Together with synonymous mutations, they might constitute at least some 40% of all mutations. These considerations suggest that neutral and nearly neutral mutations must be more common than previously considered.
The genetic control of antibody production. A study of isoimmune antibodies in cattle twins
Authors: Sellei J. , Redel J.
Published: September 2009

1. The antibody response was studied in twenty-five monozygous (MZ) and ten dizygous (DZ) pairs o f cattle twins, which were inoculated with red cells from one cattle donor carrying the M, V and U′ antigens. These red cell antigens are controlled by genes at three different loci. Most o f the recipients lacked two or all of these antigens. All had passed puberty at the onset of the experiment.

2. The antibody response against the three antigens differed markedly. Anti-U′ appeared on the average 11 days after the 1st injection and the maximum titre values were high. The V antibodies were produced at a slow rate, while anti-M was intermediate.

3. There was some influence of age on the rate and intensity of antibody production. Older animals gave a faster response and, with regard to anti-M, also higher titres.

4. Twins belonging to the same MZ pair usually produced v e r y similar antibody curves. However, there was at least one noticeable exception, which is given special consideration in the Discussion. The differences between MZ pairs accounted for a considerable portion of the variance in the different measures of antibody response and in most cases this portion remained significant also after the elimination of the influence o f age and sex. The DZ pairs were more variable.

5. The simultaneous response o f two or three antibodies in the same animal was studied. There was a significant positive association between antibody types which suggests the existence o f individual (probably genetic) differences in the general antibody-producing ability.
Fertility differences between homogamous and heterogamous matings
Authors: Cannings C.
Published: September 2009

The effect of fertility differences between homogamous and heterogamous matings are considered. The equilibria are evaluated and their stability deterimined. Completely positive and completely negative assortative mating with two and with three forms, are investigated as special cases of the above fertility structure. In these cases convergence of the genotype frequencies has beer demonstrated.
Genetic analysis of some mutations causing resistance to tetracycline inEscherichia coliK12
Authors: Reeve E. C. R.
Published: September 2009

Mutations in at least five different genetic loci cause some degree of resistance to Chloramphenicol, Tetracycline or both antibiotics inEscherichia coliK12. Two have been identified as chromosomal genes:cmlAnear λ prophage andcmlBnearpyrD. A third, giving mucoid antibiotic-resistant mutants, is probablycapR(Ion) nearlac. Another group of mucoid mutants gives marked increases in resistance to Tetracycline and in sensitivity to Puromycin; these mutants do not occur atcapR. Although all the mutations have rather small effects on resistance level, the patterns of resistance to the three antibiotics appear to be characteristically different for mutations at different loci.
Postmeiotic segregation in locus ‘46’ ofAscobolus immersus
Authors: Gajewski W. , Paszewski A. , Dawidowicz A. , Dudzińska B.
Published: September 2009

White-spored mutants ofAscobolus immersuswere used to study postmeiotic segregation within a gene. It was found that in two-point crosses between mutants showing postmeiotic segregation, polarization in recombinant asci resulting from this type of segregation resembled that in normal (even-type) conversion. However, the ratio of recombinant asci with even segregation (6:2 asci) to those with odd segregation (7:1 asci) was much higher than might have been expected on the basis of the frequencies of various recombinant asci found in crosses between the same mutants and the wild-type strain. It seems that none of the current models of recombination gives a satisfactory explanation of the results obtained.
Genetic variation in the eel: I. The detection of haemoglobin and esterase polymorphisms
Authors: Pantelouris E. M. , Payne R. H.
Published: September 2009

Electrophoretic studies on starch gel demonstrated the existence in the European eel of four haemoglobins, not two as believed from agar gel studies. The two minor fractions have been shown to be neither polymers nor methaemoglobin derivatives of the two principal fractions.

The esterase zymograms of eel sera exhibit up to eight fractions. The individual differences observed suggest genetic polymorphism and the same applies to the esterase pattern of various tissues.

This approach is of value for the collection of phenotypic frequency data with a view to solving the Atlantic eel problem.
The selection of auxotrophs ofPenicillium chrysogenumwith nystatin
Authors: Macdonald K. D.
Published: September 2009

A simple technique for the selection of auxotrophs ofPenicilhium chrysogenumafter mutagenic treatment has been devised using nystatin. It relies on the differential sensitivity of germinated and dormant conidia to nystatin and on the gradual loss of antibiotic activity which occurs on complex media at laboratory incubation temperatures. After mutagenic treatment, conidia were plated on MM agar to allow germination of prototrophs and then overlaid with CM agar containing enough nystatin to kill germinated conidia but not ungerminated auxotrophic conidia. When nystatin activity had decreased sufficiently the latter germinated and grew and thus were enriched relative to prototrophs.
Multistep transduction of tryptophan (trp) genes inEscherichia coli
Authors: Gratia J. P.
Published: September 2009

Plaque-forming transducing (pt) particles of bacteriophage ø 80 have been used to transduce genes governing tryptophan synthesis. Main interest was devoted to strains which carry deletions extending for varying distances into the tryptophan (trp) operon, coveringtrp Aand ending intrp B,trp Cor further. If the deletion does not over-reachtrp C, infection byptparticles carrying thetrp(CBA)+segment gives rise to stable partial diploids which express the complete tryptophan independence. If the deletion is further extended, transductants are not entirely complemented and appear only on medium containing indole. If the recipients do not carry any prophage in the attachment site of ø 80 (att80) the indole-requiring transductants are very unstable; if the recipients do carry such prophage, even defective, all transductants are very stable. Stable indole-requiring diploids can be superinfected by otherptphages carrying the complementary genes of the tryptophan operon, giving rise to supertransduced indole-independent bacteria. Transduction to complete independence of tryptophan or any precursor has also been achieved in three steps. Supertransductants yield after u.v. inductionptphages carrying the initialtrpsegments and segregate rare cells with incomplete ability to synthesize tryptophan. They are therefore polylysogenic polyploid heterogenotes carrying overlapping segments of thetrpoperon linked to prophage genomes.

When recipients are carrying a prophage inatt80, transductants appear at a low frequency. The reduction is particularly pronounced with ø 80pttransducing segmenttrp(CBA)+to immune bacteria.
An endonuclease-deficient strain ofUstilago maydis
Authors: Holliday R. , Halliwell R. E.
Published: September 2009

A strain ofUstilago maydishas been isolated, after treatment with nitrosoguanidine, which lacks an extracellular endonuclease capable of causing two strand breaks in DNA. Genetic analysis suggests that the strain carries two mutations and is probably also deficient in a second nuclease.
The comparison of closely related groups of rodents by DNA/DNA annealing
Authors: McLaren Anne , Walker P. M. B.
Published: September 2009

Within the genus Apodemus, DNA from A. sylvaticus and A. flavicollis could be distinguished on the basis of reciprocal DNA/DNA annealing in agar, even when unfractionated DNA was used. In preliminary experiments, DNA from geographical races of A. sylvaticus could not be distinguished, nor could DNA from two closely related species of Peromyscus.

Within the species Mus musvulus, the fast-renaturing fraction of L-cell DNA, separated on a hydroxyapatite column, was able to discriminate between L-cell (originating from the C3H inbred strain) and NZB (New Zealand Black) inbred strain DNA in agar.
The XO and OY chromosome constitutions in the mouse
Authors: Morris T.
Published: September 2009

A study was made of reproductive performance and embryonic mortality inXOandXXfemales. In the stock used, the mean litter size ofXOfemales (4·46) was greatly below that ofXXones (8·17). One series of pregnant females of both karyotypes was dissected after 15 days' gestation, and another series after 3½days' gestation. In the former, there was a significantly greater amount of embryonic mortality inXOfemales both before implantation and at the small and large mole stages. By far the greater amount occurred before implantation. The data from dissections after 3½ days' gestation concerned pre-implantation embryos, since normal embryos at this point are at the late morula or early blastocyst stage. The embryos fromXOfemales contained a large group of obviously and characteristically abnormal ones; they comprised 60/280 of the embryos fromXOfemales, compared with 4/189 of theXXones. They appeared to have developed abnormally from a very early stage, probably the two-cell stage, and were considered to represent the missingOYclass of zygotes. In addition, it was concluded that there was probably an abnormally low segregation of nullo-Xgametes fromXOfemales.
Resistance ofEscherichia colito penicillins: IV. Genetic study of mutants resistant to D, L-ampicillin concentrations of 100 μg/ml.
Authors: Boman Hans G. , Eriksson-Grennberg Kerstin G. , Normark Staffan , Matsson Eva
Published: September 2009

The first two steps towards increasing ampicillin resistance inEscherichia coliconcern the genesampAandampBwhich are located at least 20 min from each other (Eriksson-Grennberget al.1965 and the two preceding papers). This paper describes a third class ofampA-containing mutants (designatedampAB) which are resistant to D, L-ampicillin concentrations of 100 μg/ml. When such as F-strain (D31) was crossed to different Hfr strains analysis of thetrp+andproB+recombinants indicated that resistance genes were located betweentrpandproB. Altogether five classes of recombinants were produced but only the two genesampAandampBwere recovered. One interpretation suggested is that the resistance of D31 is due to the presence ofampAandampBand a chromosomal aberration by whichampAwas moved to a position nearampB. It was possible to transduce both intermediate levels of resistance as well as the full resistance of anampABdonor strain, but the strains produced were unstable. In crosses the presence ofampABin the recipient reduced the number of recombinants by reducing the number of stable pairs. In an Hfr strainampABwas shown to give rise to additional difficulties in establishing the cell contact during mating. Some ampicillin resistant mutants also showed decreased ability to propagate the RNA phage MS2.
The introduction of genetic material from inferior into superior strains
Authors: Osman H. El Sayed , Robertson Alan
Published: September 2009

1. A series of experiments have been carried out withDrosophila melanogasterin order to improve further a population, highly selected for a quantitative character, by introducing genetic material from an inferior population. The effects of selecting the latter before crossing to the selected line, of waiting after crossing before restarting selection and of varying the intensity of selection after crossing have been studied. The inferior population used was the large random breeding population from which the selected line had been produced by selecting downwards for sternopleural bristles.

2. There proved to be some incompatibility between the conditions necessary to achieve the two criteria of success—the time to surpass the selected line and the extent by which it was eventually exceeded. The lines which surpassed it soonest had not been selected before crossing and had been selected intensely immediately afterwards. Those which surpassed it most had had the greatest amount of selection before crossing followed by the most intense selection afterwards.

3. Crossing-over did not appear to be a limiting factor after crossing. Neither a period of relaxation after crossing nor a lower intensity of selection after crossing increased the chance of success.

4. Genetic analyses were made of several lines which had exceeded the original selected line. In separate lines, second, third and fourth chromosomes were found which were superior to the chromosomes of the selected line. This and other evidence shows that the limits in such lines with a small number of parents are not in any way absolute but artefacts of the selection programme. The extreme third and fourth chromosomes were both recessive to that of the selected line in the effect on bristle score.

5. A theoretical discussion of such selection programmes is given, assuming that the character is controlled by independently segregating loci. It is shown that, if two alleles at different loci have an equal but small chance of fixation in the initial selection, one because it is rare and the other because, though frequent, it has little effect on the character, such a programme will tend to pick up the former rather than the latter. Of two such rare alleles with an equal initial chance of fixation, the one additive and the other recessive, the chance of fixation of the latter will be greater in a crossing programme.
The effects of population size and selection intensity in selection for a quantitative character inDrosophila: I. Short-term response to selection
Authors: Frankham R. , Jones L. P. , Barker J. S. F.
Published: September 2009

1. The response to selection for increased number of bristles on one abdominal segment was studied over 12 generations using a factorial design of three population sizes (10, 20 and 40 pairs of parents) and five selection intensities (10, 20, 40, 80% and controls).

2. The responses on the average agreed well with those expected from the estimated base population heritability, but individual replicates diverged considerably.

3. Larger populations tended to give greater response to selection, due mainly to larger realized heritabilities.

4. There was no consistent effect of selection intensity on realized heritability.

5. For populations with the same number of individuals scored, less intense selection gave greater realized heritabilities.
The effects of population size and selection intensity in selection for a quantitative character inDrosophila: II. Long-term response to selection
Authors: Jones L. P. , Frankham R. , Barker J. S. F.
Published: September 2009

1. An experimental evaluation of Robertson's (1960) theory of limits in artificial selection was attempted. A number of lines from the Canberra base population were selected for abdominal bristle number over 50 generations with population sizes of 10, 20, and 40 pairs of parents and selection intensities of 10, 20 and 40% as well as unselected controls.

2. In general, the total response obtained increased with an increase inNī(product of population size and standardized selection differential).

3. Thus, total response increased with increase in the number of individuals scored, or, for a fixed number of parents, increase in selection intensity increased both rates of response per generation and total response.

4. But for the same total number scored, the response increased as selection intensity decreased. However, the proportion selected had only a small effect as compared with that of the total number scored.

5. Sublines in which the population size was reduced after 16 generations of selection but with the selection intensity kept constant, immediately fell behind their parent lines and gave much less response.

6. Agreement between replicate lines was generally poor, particularly for the 10- and 20-pair lines.

7. Patterns of response in individual lines were frequently irregular and ‘waves of response’ were not uncommon.

8. The results are discussed in terms of several theoretical models of selection limits. In general, agreement with these models was poor, as much of the response appeared to be due to a few genes (or gene combinations) with large effects on bristle number.
Growth rate and haploidization ofAspergillus nigeron medium containingp-fluorophenylalanine
Authors: Lhoas Pol
Published: September 2009

1. The comparison of the dry weight of thin layer haploid and diploid colonies ofA. nigeron complete medium and complete medium supplemented withp-fluoro-phenylalanine led to the conclusion that there is a difference in growth rates of hyphae under these different conditions.

2. The growth curves of the same strains on both media were established. On complete medium, haploids and diploid show a growth rate increasing linearly for about 20 h after germination and reaching a maximum which is then maintained. Onp-fluorophenylalanine, the haploids show a similar curve, although the maximum growth rate reached and maintained is about half that on complete medium; for the diploid, however, the maximum is less than the corresponding one in the haploid and, once this maximum has been reached, the growth rate goes down linearly to a very low value which is then maintained.

3. The cytological study of the hyphal tip cell showed, in the presence of the amino acid analogue, a reduction of the mean size of the diploid nuclei together with an increase of the number of nuclear fragments. This explains the growth rates observed and is accepted as a confirmation thatp-fluorophenylalanine, by its action on the mitosis, favours chromosome losses which lead finally to the production of haploid nuclei.
Aegilops×Secalehybrids: the production and cytology of diploid hybrids
Authors: Majisu B. N. , Jones J. K.
Published: September 2009

Hybrids between four diploid species ofAegilopsand species ofSecalewere obtained by using embryo culture. There was a marked incompatibility in the crosses betweenSecalespecies and each of the four species in Section Sitopsis ofAegilopsandAe. mutica. It is suggested that this genetic incompatibility withSecalespecies is an additional similarity between these species ofAegilopsand the diploid species ofTriticum.

Most chromosomes ofAegilops(A) andSecale(S) are univalent during meta-anaphase of meiosis in these hybrids, but some appeared to associate and others to pair as apparently normal chiasmate bivalents. Analysis of non-chiasmate and chiasmate associations showed that the frequencies of autosyndetic (AA and SS) and allosyndetic (AS) associations fitted the 3AA: 7AS: 3SS ratio expected if association and pairing is at random. Any deviations from random involved a deficiency rather than an excess ofAegilops-Secalepairing. There is no evidence that the chromosomes ofSecaleare homologous with those ofAe. caudata,Ae. comosaandAe. umbel-lulata, and it is suggested that the genome ofSecalespecies does not show any homology with the genomes of the generaAegilops. This does not preclude the presence of homologous segments. It is suggested that the possibility of random association of chromosomes should be considered when occasional pairing in interspecific hybrids is analysed, and that identification of chromosomes and recognition of chiasmata are required. The possibilities of chiasmata between non-homologous chromosomes, of a genetic mechanism in rye which suppresses the pairing of homoeologous chromosomes, and of other factors causing asynapsis and pseudo-synapsis between genetically similar chromosomes are discussed.
Genetical and structural analyses of cell-wall formation in Chlamydomonas reinhardi
Authors: Davies D. Roy , Plaskitt A.
Published: September 2009

Fifteen mutant strains of Chlamydomonas reinhardi were isolated which showed defects in some aspect of the process of cell-wall formation. Genetic analyses indicated that most of the mutations were due to single gene changes; two were anomalous in that non-Mendelian segregations were obtained on crossing with other genotypes, and on selfing they frequently gave rise to wild-type phenotypes.

Occasional somatic revertants were also obtained from these two strains. On the basis of these analyses it is suggested that there are two levels of control operating in the process of cell wall biogenesis - one concerned with subunit production at the nuclear level and another, possibly concerned with three-dimensional organization, at another level. Electron-microscope analyses of the different mutants showed the mutants to be divided into three main categories: those in which the wall was formed but was not attached to the plasma membrane, those in which the wall was attached to the membrane, and those in which very little wall was formed. In the last class in particular, vesicles containing wall precursors were clearly visible, and were shed through the plasma membrane into the medium.
Gene conversion: remarks on the quantitative implications of hybrid DNA models
Authors: Gutz Herbert
Published: September 2009

Some quantitative implications of the gene conversion models of Holliday and Whitehouse & Hastings are discussed. These models predict two kinds of mispairing when a heterozygous mutant is in hybrid DNA. It is pointed out that the latter model, in contrast to statements in the literature, does not require identical repair rates in both kinds of mispairing.

Furthermore, some peculiarities are discussed which result if, among the corrected fractions of hybrid sites, the frequency of repair to wild-type is the same in both kinds of mispairing (r=s). In the Holliday model a minimum results under this condition for the frequency of asci which show a normal 4:4 segregation, but which have originated by repair from meioses with hybrid DNA.
A genetic analysis of therudimentarylocus ofDrosophila melanogaster
Authors: Carlson Peter S.
Published: September 2009

A study of the structural and functional organization of therudimentary(r: 1–54·5) locus ofDrosophila melanogasterhas demonstrated that alleles of this gene reside in a number of recombinationally separable sites, and display a complex pattern of interallelic interaction. Data relating to interallelic interaction have been utilized to construct a linear complementation map consisting of 7 complementation units and 16 complementation groups. Comparison of the genetic fine structure map and the complementation map shows that the two maps are approximately co-linear. Totally non-complementing alleles reside at both ends of the fine structure map. Therlocus is best interpreted by the model of a single cistron whose product affects several distinct developmental processes and whose alleles display a complex pattern of interallelic complementation. Intragenic recombination within therlocus is accompanied by the appearance of parental and recombinant flanking marker classes not expected on the basis of reciprocal recombination. Studies with half-tetrads demonstrate that intragenic recombination can occur either by gene conversion or by a reciprocal exchange mechanism. The pattern of organization seen at therlocus is similar to patterns of organization found in work with fungal genes.
Evidence for allelism of leaner and tottering in the mouse
Authors: Tsuji Shigekatsu , Meier Hans
Published: September 2009

We found thatlais located in linkage group XVIII. It is highly probable thatlaandtgare alleles, and closely, linked toEs-1. Mice of the genotypela/tgare abnormal, with clinical signs similar totg, although more severe. They develop earliest signs at about 15 days of age, similar tola, are runted but fertile and can live for months. Clinical signs are ataixa, stiffness, retarded motor activity and intermittent focal seizures. The pathological basis for these symptoms is still elusive. The three types of mice,la/la,la/tgandtg/tgare thus distinct clinically,la/tgresembling in some respect either of the other two.
The highly polarized recombination pattern within the methA gene ofAspergillus nidulansRecombination within the methA cistron ofA. nidulans
Authors: Putrament Alexandra , Rozbicka Teresa , Wojciechowska Katarzyna
Published: September 2009

The recombination between the methA alleles ofAspergillus nidulansis very strongly polarized. The mutants can be mapped in respect to each other and in respect to the flanking markers, both on the basis of the relative frequency of one of the P classes and one of the R classes. In all crosses it is the distal mutant which converts predominantly.

In one combination of the mutants crossed the low temperature at which meiosis proceeded increased recombination frequency and modified the recombination pattern.
Salmonella hybrids containing genic material of multiple origins
Authors: Armstrong F. B. , Sprague George F.
Published: September 2009

Bacterial hybrids were produced to contain genetic material ofSalmonella typhimurium, Escherichia coli, S. montevideoandS. abonyorigins. Analyses by transduction provide evidence that 6% of the originaltyphimuriumgenome has been replaced in the production of these hybrids. Although a number of biosynthetic pathways are affected by this gene substitution, the growth rate of these hybrids in minimal medium is unchanged. Supporting evidence for the close relatedness betweenS. typhimuriumand the other three species is not observed in recombination studies. Available results favour the concept that differences in base sequences are responsible for the low frequency of recombination obtained in heterologous crosses.
Gene conversion in higher organisms: Non-reciprocal recombination events at the rosy cistron inDrosophila melanogaster
Authors: Ballantyne G. H. , Chovnick Arthur
Published: September 2009

Analysis of a series of exceptionalry+half-tetrads, produced in mass matings involving rosy mutant heterozygous half-tetrads, provides rigorous demonstration of the occurrence of non-reciprocal as well as reciprocal recombination events within the rosy cistron ofDrosophila melanogaster. Inferences about allele recombination drawn from this and other studies in Drosophila provide a strong argument that gene conversion occurs as a regular event in higher eukaryotes.
Development and complementation of lethal mutations at the dumpy locus ofDrosophila melanogaster
Authors: Metcalfe Judith A.
Published: September 2009

The genetical and developmental aspects of six dumpy mutants ofDrosophila melanogasterhave been investigated. The mutantsobm,lmandolv(possibly alleles),lv, lv1andlvI(possibly alleles) were known to be lethal when homozygous. Previously the lethal effect has been treated as a uniform effect. However, the lethal stage is not the same for all homozygotes, being egg/larval (E/L) for the threelvalleles, egg (E) forolv, larval/larval ecdysis (L/L) forlmand E/L and larval (L) forobm. Not all heterozygous combinations are lethal, i.e.obm/lmandobm/lvIare not lethal. Phenotypically the lethal heterozygotes fall into two patterns: (i) combinations not involving the alleleobmand (ii) combinations involvingobm. In the former, the mutant with the developmentally later expression is ‘dominant’ to the mutant with the developmentally earlier expression. In the latter, the genotypes manifest different proportions of individuals at the lethal stages E, E/L and L. Previous observations suggested that the lethality of the homozygoteobm/obmwas associated with the presence of an independent lethal in the stock. Observations presented here suggest that the lethality is a function of theobmallele itself. Complementation between some of the lethal mutants is not in accordance with the general rule for dumpy that compounds manifest the traits they have in common.
Genetic analysis ofsulmutants ofEscherichia coliB
Authors: Donch John J. , Chung Young Sup , Green Michael H. L. , Greenberg Joseph , Warren Guylyn
Published: September 2009

Thesulgene of B/rw (Witkin) and 26 independently isolatedsulmutants were examined for their suppression of radiation sensitivity. The suppressedlongene was demonstrated by transducing it into a K12proCrecipient. Thesulgene of B/rw and all but one of the B/r mutants was found to be linked to a gene controlling azide resistance. Transduction data established the order of markers asleu azi mutT sul. One B/r mutant was found not transducible with azide resistance,sulmutations were found to suppress the capsular polysaccharide production oflonstrains.
Biochemical investigation of the slow-growing non-perithecial (sgp) mutants ofAspergillus nidulans
Authors: Houghton J. A.
Published: September 2009

Using polarography the uptake of oxygen by intact and homogenized mycelium of a wild-type strain and strains of slow-growing non-perithecial (sgp) mutants was compared. It was found that whilst the oxygen uptake of intact, wild-type mycelium increased on the addition of glucose or succinate as substrate, uptake of oxygen by mutant mycelium increased only when glucose was used as substrate and was unaffected by succinate. When, however, homogenates of mutant mycelium were used oxidation of the succinate occurred. It was concluded that the inability of the mutants to utilize succinate was due to their impaired ability to take up the compound across the hyphal wall and this was confirmed using radioactively labelled substrates. It is tentatively suggested that the abnormal growth of thesgpmutants on glucose medium and their impaired permeability to tricarboxylic acid cycle intermediates may be due to reduced availability of high energy compounds caused by a lesion in their oxidative phos-phorylation system.
A technique for replica platingCoprinus lagopus, a filamentous fungus
Authors: Kaplan Philippa J. , Walls D.
Published: September 2009

The problem of replica plating filamentous fungi such asCoprinus lagopusis overcome by inducing micro-colonies with sodium deoxycholate and using ‘Velcro’, a hooked material, to replace velveteen in the standard replica plating technique. ‘Velcro’ is advantageous in that it has a regular pattern of closely spaced hooks which transfer small inocula from the colonies on the master plate.
The nature of the purebred-crossbred genetic covariance
Authors: McNew Ronald W. , Bell A. E.
Published: September 2009

Epistatic models are examined for conditions which result in a negative covariance between a sire's purebred and test-cross progenies. It is found that heterozygote superiority is not a necessary condition for its occurrence. The frequencies of the same allele in the selected population and in the tester should be divergent. The implications of using the covariance in prediction are discussed. The important result to note is that selection in the crossbred may not be optimum even with a negative covariance.
Isoenzymes and polyploidy I. Qualitative and quantitative isoenzyme studies in the Triticinae
Authors: Mitra R. , Bhatia C. R.
Published: September 2009

Isoenzymes of alcohol (ADH), malate (MDH), glutamate (GDH) and isocitrate (IDH) dehydrogenases, and a fast migrating esterase (EST-l) were separated by disk electrophoresis from dry seed extracts of diploid, tetraploid, hexaploid and octaploid species or amphiploids belonging to the subtribe Triticinae. Only ADH and EST-l isoenzymes showed inter-species variation; the other dehydrogenases, which show stringent substrate specificities (‘critical’ enzymes), revealed the same pattern in all diploid and polyploid species. The qualitative zymogram studies showed that (1) the number of variant enzyme bands increased with the level of ploidy, (2) the amphiploid isoenzyme pattern was additive of the parental species, (3) enhancement in the number of bands was due to the presence of not only parental bands, but also hybrid bands formed by association between heteromonomers. Quantitative data were obtained by densitometry of the enzyme bands as well as spectrophotometric measurements of enzyme activity in crude extracts. Increase in the level of enzyme activity was observed with ploidy level. In spite of the evidence that all duplicate/triplicate genes are expressed, increased enzyme activity observed in the polyploid species was not proportional to the level of ploidy or expected gene dosage. On the basis of ADH and EST-l zymograms obtained in 2 × and 4 × wheat, probable zymograms for these enzymes in the B-genome donor to 4 × wheat were extrapolated. NeitherAe. speltoidesnorAe.bicornisshowed the extrapolated ADH pattern. Amphiploids involvingAe.speltoidesandTriticum monococcumorT. aegilopoidesfully reproduced the EST-l zymogram of 4 × wheat, but not the ADH.Ae. bicornis×T. aegilopoidesamphiploid showed an ADH zymogram similar to that of 4 × wheat, but the EST-l bands were different.
Genes and genotypes affecting embryonic fluid relations in the mouse
Authors: Johnson D. R.
Published: September 2009

The contribution of maternal and foetal genotype to the regulation of extra-embryonic (exocoelomic and amniotic) fluid and embryonic fluid in the mouse is discussed. Three of the four inbred strains studied (A, BALB/c and CBA) had similar patterns of fluid accumulation. The fourth (C57BL) differed significantly. In the reciprocalF1crosses between CBA and C57BL a maternal effect was present. In theF2no increase in variance of extra-embryonic fluid was noted.

The effects of two mutant genes were studied. Blebs (my) had no effect on the total fluid in the conceptus, but led to a rearrangement of fluid within the embryo. Brachyphalangy (Xtbph) caused an overall increase in fluid within the conceptus. Distribution of the excess depended upon the phenotype (exencephalic versus non-exencephalic) of the embryo.
Recombination and chromosome structure in eukaryotes
Authors: Putrament Aleksandra
Published: September 2009

Allelic recombination frequency and pattern in fungi show strong gene-to-gene variation. At least in two fungal species,NeurosporaandSchizophyllum, recombination frequencies in certain chromosomal segments are genetically determined. The possibility that chromosomal proteins and/or synaptinemal complexes may play an important role in regulation of recombination frequency and pattern is discussed.
An estimate of heterosis inDrosophila melanogaster
Authors: Sved J. A.
Published: September 2009

Twenty-five population cages ofD. melanogasterwere set up, each containing a different wild-type second chromosome and the marker chromosomeCy. In all but one case where contamination apparently occurred, theCychromosome persisted in the population at high frequency, showing a selective advantage ofCy/ + heterozygotes over wild-type homozygotes. Overall, the results indicate that homozygosity of the entire second chromosome causes a depression in fitness of the order of 85%.
The flagella of temporary dikaryons ofChlamydomonas reinhardii
Authors: Starling David , Randall John
Published: September 2009

The structure and function of flagella are genetically determined and single gene mutants – for example, lacking in motility or of abnormal flagellar length – have previously been investigated. When such mutants are crossed with wild-type, temporary dikaryons – prozygotes – are formed with two nuclei and a common cytoplasm. The properties of the four flagella – two originally abnormal – have been observed as a function of time. In wild-type × non-motile mutant crosses, restoration of motility has been observed in a number of cases. If the dikaryons are deflagellated regeneration occurs, together with restoration of motility or of normal length to the previously abnormal pair. Complementation at the cytoplasmic level has been found in paired mutants.
Further observations on the correlation between kappa and phage-like particles in paramecium
Authors: Grimes Gary W. , Preer John R.
Published: September 2009

It has been possible to examine the correlation between the presence of phage-like particles and R bodies by using serial sections of kappas of stock 562. No exception has been found to the rule that 562 kappa particles with R bodies also have phage-like particles; however, 3 out of 78 kappa particles with phage-like particles lacked R bodies.
Rates of spontaneous mitotic recombination inSaccharomyces cerevisiae
Authors: Thornton R. J. , Johnston J. R.
Published: September 2009

The rates of mitotic recombination at the lociade3,ade5–7,ade6andade8were approximated by the method of ‘increasing proportion of variants with growth’. The values (per cell generation) were 3·5 × 10−4forade8, 1·4 × 10−4forade5–7, 4·0 × 10−5forade3and < 2 × 10−6forade6. The relative frequencies of mitotic recombination in regions betweenade 5–7and the centromere were different from those obtained with radiation-induced recombinants.
Multiple recombinational events within the84 Wlocus ofAscorolus immersus
Authors: Paszewski A. , Prażmo W. , Jaszczuk E.
Published: September 2009

Multiple recombinational events within a gene were studied by tetrad analysis of multipoint intragenic crosses. It was found that a considerarle proportion of double-site conversions can arise as two separate but correlated events. The same was true for conversion and crossing-over associated with it. The data point to a possibility of multiple recombinational events involving both conversions and cross-overs, occurring as successive rounds of recombination within a single recombinational process. Some of the results suggest that more than two chromatids may be involved in such a process. The results are discussed in terms of different recombination models.
Wheat mutants permitting homoeologous meiotic chromosome pairing
Authors: Wall A. M. , Riley Ralph , Chapman Victor
Published: September 2009

Plants of Triticum aestivum (2n = 6x = 42) ditelocentric 5BL were treated with EMS in order to produce mutations in the 5B system by which meiotic pairing between homoeologous chromosomes is normally prevented. To check for the occurrence of mutation T. aestivum ditelo-5BL plants were pollinated with rye (Secale cereale 2n = 14) and meiosis was examined in the resulting hybrids.

Wheat-rye hybrids were scored for the presence of mutants when the wheat parents were either the EMS-treated wheat plants, or their selfed derivatives, or their progenies obtained after pollination with untreated euploid individuals.

Mutants were detected by each of these procedures and mutant gametes were produced by the treated ditelocentric plants with frequencies between 1·5 and 2·5%, but there were differences between the mutants in the extent to which homoeologous pairing occurred in the derived wheat-rye hybrids. The differences may have resulted from the occurrence of mutation at different loci or to different extents at the same locus.

Two mutants, Mutant 10/13 and Mutant 61, were fixed in the homozygous condition. Mutant 10/13 was made homozygous both in the 5BL ditelocentric and in the euploid conditions but these genotypes regularly formed 21 bivalents at meiosis, and there was no indication of homoeologous pairing although the mutant 10/13 gave rise to homoeologous pairing in wheat-rye hybrids.
A simple technique for the identification of chain termination suppressor mutants in species ofSalmonella
Authors: Hedges R. W.
Published: September 2009

Chain-termination suppressors which are almost certainly amber suppressors have been isolated inSalmonella anatumby a technique involving the use of amber mutants of bacteriophage 01. The same technique could be used in any species ofSalmonella(and many strains of Arizona) and analogous techniques are suggested for use in other genera of bacteria and in higher plants.
The genetic analysis of the direct and correlated response to selection for chaetae inDrosophila melanogaster
Authors: Scowcroft W. R.
Published: September 2009

The direct and correlated response to selection of scutellar microchaetae and scutellar bristles has been analysed by determining the contribution of the three major chromosomes, alone and in combination with each other, to the overall response. The results of the analysis confirm a previous finding, based on a formal statistical approach, that response to selection for microchaetae had highly pleiotropic effects on scutellar bristles. In lines selected, each for high and low microchaetae, genetic changes in the 2nd and 3rd chromosomes are pre-eminent and essentially equal. Inter-chromosomal interactions are of relatively minor importance in interpreting the response to selection for microchaetae but assume greater importance with respect to the correlated character. The results are discussed in terms of the genetic correlation between fitness and the character measured.
The maintenance of the genetic variability of polygenic characters by heterozygous advantage
Authors: Bulmer M. G.
Published: September 2009

The results of a previous paper on the effect of optimizing selection, mutation and drift on a metric character determined by a large number of loci have been extended to include the possibility that, in addition to selection for an optimal value, there may be independent selection in favour of heterozygotes; it is assumed for simplicity that at each locus the heterozygote has the same advantage,s, over each of the homozygotes. Under selection alone there is a stable equilibrium ifs>ca2, wherecis a measure of the intensity of the optimizing selection andais the effect of a gene substitution. Under the additional forces exerted by mutation and by drift due to finite population size each locus behaves independently of the other loci as if it had a heterozygous advantage equal to (s−ca2).
Genetic differences between populations of Drosophila melanogaster for a quantitative trait: II. Wild and laboratory populations
Authors: López-Fanjul C. , Hill W. G.
Published: September 2009

Crosses were made between four populations of Drosophila melanogaster – three of which were laboratory populations (Kaduna, Pacific and Canberra) and one recently captured (Stellenbosch) – and a line previously selected for low sternopleural bristle number for many generations from a Kaduna/Pacific source. In each of six replicate lines from each cross selection was practised for low sternopleural bristle number, and subsequently these replicates were intercrossed and reselected.

Initially, similar responses were made in each set of lines, but subsequently more variation between replicates was found in Stellenbosch, which was the primary source of lines which responded to a level below that of the original selected line.

It is concluded that this newly captured population contains genetic variability absent from the laboratory populations. Presumably variability has been lost from the latter populations, leaving essentially the same genes segregating in each.
Effects of gene dosage and hormones on the expression of Dr in the platyfish,Xiphophorus maculatus(Poeciliidae)
Authors: Valenti Robert J. , Kallman Klaus D.
Published: September 2009

Platyfish,Xiphophorus maculatus, are polymorphic for the patterns red-dorsal (Dr) and spotted-dorsal (Sd) fins, both controlled by closely linked loci on theXchromosome of Jamapa strain, Jp 163A. The intensity of red pigment looks the same in males and females, but spectrophotometric analysis of dorsal fin extracts showed that heterozygous intact males have significantly more red pigment (drosopterin) than homozygous or heterozygous females or castrated males. The mechanism of Dr expression in Jamapa is, thus, similar to the one present in the Belize stock, where a sex difference is readily apparent that is known to be under androgenic control. The Sd phenotype is identical in both sexes.SdandDrare not restricted to theXchromosome, and no evidence for gene dosage compensation has been obtained. Within the Jamapa stock the expression of Sd and Dr are best described in terms of dominance and recessiveness. Dr is strongly augmented by a testicular hormone.DrandSdhave been separated by crossing-over. In natural populations both genes can occur by themselves, linked to each other or to other pigment genes. The development of the Sd macromelanophores is not contingent upon the presence of pterinophores (Dr) in the dorsal fin or elsewhere in the body.
Genetic control of recombination inSchizophyllum commune: evidence for a new type of regulatory site
Authors: Stamberg Judith , Koltin Y.
Published: September 2009

Two strains ofS. communecharacterized by different levels of high recombination frequency in a particular region of the genome (between the two subunits, α and β, of theBincompatibility factor) were crossed, and their progeny tested for recombination frequency in the same region. The difference between the strains in recombination frequency is found to be due to some factor located within the recombining region itself.

The segregation among the progeny indicates that the factor consists of a number of sites, with additive effects. This and the dominance relationships suggest that these sites may be recognition sites which comprise a part of the fine control of recombination.
An incompatibility system determined by three factors in a species of Psathyrella (Basidiomycetes)
Authors: Jurand M. K. , Kemp R. F. O.
Published: September 2009

Evidence is given for a trifactorial system of incompatibility in an isolate identified as Psathyrella coprobia. The three factors are designated A, B and C. They are thought to be inherited independently. The function of factor A is most probably the same as that of factor A of bifactorial species. Factor B is concerned with the initiation of fruit body primordia, while all three factors must be heterozygous for the occurrence of nucleár migration and the formation of mature fruit bodies.