bluuebunny/crossref_metadata_2025 huggingface dataset:
Development ofDrosophilaon sterol mutants of the yeastSaccharomyces cerevisiae
Authors: Bos Marten , Burnet Barrie , Farrow Roy , Woods Robin A.
Published: September 2009

Four species ofDrosophila (melanogaster, simulans, mauritianaandvirilis) were tested for their ability to survive onergstrains ofSaccharomyces cerevisiaeeach having a mutant block at a different reaction in the synthesis of ergosterol. Species capable of completing development on a given yeast mutant strain were tested for egg production and viability, and also for their ability to survive on the mutant yeast for five complete generations. Sterol analyses using gas–liquid chromatography show that the sterol composition of flies closely resembles that of the yeasts on which they are grown, confirming that the steric criteria for sterols capable of a structural role in lipoprotein membranes are relatively broad. Even so, different sterols are not equally efficient in this respect and there are differences between species in their tolerance to the sterols available from each of the yeast mutants. The range of sterols capable of satisfying the micronutrient, as distinct from the macronutrient, requirement is narrower. Growth on two of the yeast mutants (erg-2anderg-6) leads to developmental arrest in the larval stage due, it is suggested, to a block in the synthesis of ecdysone. The fourDrosophilaspecies lack an effective level of Δ8−Δ7isomerase which is necessary for utilization of zymosterol and other Δ8sterol precursors of ergosterol. Ergosta-5,7-diene-3β-ol appears to be capable of substituting for cholesterol in the metabolism ofDrosophila.
The transient distribution of allele frequencies under mutation pressure
Authors: Nei Masatoshi , Li Wen-Hsiung
Published: September 2009

The transient distribution of allele frequencies in a finite population is derived under the assumption that there arekpossible alleic states at a locus and mutation occurs in all directions. At steady state this distribution becomes identical with the distribution obtained by Wright, Kimura and Crow whenk= ∞. The rate of approach to the steady state distribution is generally very slow, the asymptotic rate being 2v+ 1/(2N), wherevandNare the mutation rate and effective population size, respectively. Using this distribution it is shown that when population size is suddenly increased, the expected number of alleles increases more rapidly than the expected heterozygosity. Implications of the present study on testing hypotheses for the maintenance of genetic variability in populations are discussed.
The combinations of the sexes in twin lambings
Authors: James William H.
Published: September 2009

Evidence is presented that the distribution of the combinations of the sexes in twin lambings has subnormal dispersion: there are more opposite-sexed pairs than same-sexed pairs. When adjustment is made for the occasional presence of monozygotic twin pairs, the departure from expectation (on the assumption that the sexes of DZ twins are distributed binomially) is highly significant. Thus sheep litters seem to show a feature characteristic of litters of pigs and (probably) mice and rabbits. This is consistent with the suggestion that p, the probability of a male zygote, varies systematically from one zygote to another within a litter.
RP4 Fertility Variants inAcinetobacter calcoaceticus
Authors: Towner K. J. , Vivian A.
Published: September 2009

The resistance plasmid RP4 can be used to mediate conjugation inAcinetobacter calcoaceticus. Transfer of chromosomal genes occurs only on solid surfaces and not in liquid matings. Two RP4-carrying donor strains which donate the chromosome in different directions from different origins have been isolated. As a result it is possible to demonstrate that the linkage map ofA. calcoaceticusis circular.

The fate of RP4 in recombinants was examined. Although frequent loss of the complete plasmid was detected, segregation of plasmid antibiotic resistances was not observed.

A possible mechanism by which RP4 could interact with theA. calcoaceticuschromosome is discussed.
Isolation and Analysis of Amoebal–Plasmodial Transition Mutants in the MyxomycetePhysarum polycephalum
Authors: Anderson R. W. , Dee Jennifer
Published: September 2009

Plasmodium formation in the MyxomycetePhysarum polycephalumnormally involves fusion of haploid amoebae, carrying different alleles at the mating type (mt) locus, to give diploid plasmodia. Strains carrying themthallele are capable of undergoing the amoebal–plasmodial transition with high efficiency within amoebal clones, resulting in the formation of haploid plasmodia. NMG mutagenesis ofmthamoebae, followed by an enrichment procedure, was used to isolate mutants in which such clonal plasmodium formation was either delayed or absent. Thirteen mutants of the second type were analysed. Three of these were temperature-sensitive for plasmodium formation. All thirteen mutants were able to form diploid crossed plasmodia when mixed with amt1strain. Three new genes were identified and designatednpfA,npfB andnpfC. A mutant allele ofnpfA renderedclonalplasmodium formation temperature-sensitive, but did not prevent crossing at the non-permissive temperature with derived strains carrying the same mutant allele. No recombination was detected betweennpfB ornpfC andmt, butnpfA was unlinked tomtand a locus (apt-1) shown in a previous study to be involved in plasmodium formation. The genesnpfB andnpfC were distinguished by complementation analysis. Strains of the genotypenpfB−;npfC+behaved in the same way as strains carrying themt2allele. The nature of the mutants and the role of the mating-type locus in the initiation of plasmodium formation are discussed.
Mutagen specificity in conversion pattern inSordaria brevicollis
Authors: Yu-Sun C. C. , Wickramaratne M. R. T. , Whitehouse H. L. K.
Published: September 2009

A total of 39 mutants at thegrey-3,grey-4andgrey-5spore colour loci inSordaria brevicollishave been investigated for conversion pattern by crossing them with wild type and counting aberrant asci. Twenty-one of the mutants were obtained with ICR170 and all showed postmeiotic segregation only rarely (0–8% of the aberrant asci); two showed conversion predominantly to wild type (class A) and the other 19 predominantly to mutant (class B). Six mutants were obtained with ethylmethane sulphonate and one with nitrosoguanidine, and they all showed postmeiotic segregation frequently (14–54% of the aberrant asci) and conversion usually about equally frequently in each direction, though with considerable diversity between mutants (class C). Eleven UV-induced mutants comprised one of class B and ten of class C. There was considerable variation in aberrant ascus frequency between alleles, but conversion pattern seemed to be independent of this frequency.
Variability in genetic parameters among small populations
Authors: Avery P. J. , Hill W. G.
Published: September 2009

For a model in which quantitative traits are assumed to be determined solely by additive genes at many loci, formulae are developed for the variance among replicated small populations of sizeN, maintained without selection, of the additive genetic variance, heritability, genetic correlations and similar parameters. The base population is assumed to be in linkage equilibrium, but it is argued that most of the variation in the within-line additive variance (VAtat generationt) is due to linkage disequilibrium caused by sampling. Ifis the squared correlation of gene frequencies averaged over all pairs of loci at timet, the coefficient of variation (CV) ofVAtequals, with similar formulae for other parameters.

The formulae are evaluated for models of loci distributed uniformly along the chromosome but much of the disequilibrium is due to loci on different chromosomes. For unlinked loci CV(VAt) reaches √4/(3(N)), and for mammalian models, this value is not greatly exceeded. The variance in successive generations has a correlation of at least one-half due to the maintenance of linkage disequilibrium. The magnitude of this variance in parameters and their autocorrelation with time shows that accurate predictions cannot be made about genetic parameters in the base population from single replicate results.
Studies on male recombination in a Southern GreekDrosophila melanogasterpopulation: (a) Effect of temperature. (b) Suppression of male recombination in reciprocal crosses
Authors: Yannopoulos George , Pelecanos Michael
Published: September 2009

A second chromosome ofDrosophila melanogaster(symbol 31.1) isolated from a natural population of North-Western Peloponnesus (at a distance of 8 km from the city of Patras) was found to induce recombination in heterozygous males, both in the second and third chromosomes. The present study also revealed the following points. (1) The phenomenon is temperature-sensitive with higher male recombination at 29 °C than at 25 or 15 °C. (2) The temperature-sensitive period is during the larval stage where premeiotic divisions of germ cells take place. (3) Suppression of male recombination in both the second and third chromosomes occurred when 31.1/CyL4females were used in the matings, and (4) the suppression of male recombination is caused by a cytoplasmic factor of theCyL4/Pmstock.
Selection oflonmutants inEscherichia coliby treatment with phenothiazines
Authors: Molnár J. , Holland I. B. , Mándi Yvette
Published: September 2009

Growth ofE. coliK12 in the presence of chlorpromazine or promethazine resulted in the appearance of a special kind of mutational change with a frequency of 5–10%. These cells were UV-sensitive and very mucoid in their colony formation. The strains were characterized as colanic acid producing on the basis of phage m-59 sensitivity and we tentatively conclude that these mutants are Lon−.

In another series of experiments drug treatment ofE. colifailed to yield significant numbers of auxotrophs and the back mutation rate of a number ofS. typhimuriumHis−strains was not significantly increased.
Reciprocal differences in female recombination associated with hybrid dysgenesis inDrosophila Melanogaster
Authors: Kidwell Margaret Gale
Published: September 2009

Large reciprocal differences in recombination frequencies were observed in F1female progeny of a number of strain crosses. These reciprocal effects on recombination were found in several intervals of all three major chromosomes; they were greatest in intervals proximal to or spanning the centromere but were also found in some distal regions. The direction of recombination change was not consistent over different chromosomal intervals. There was no clear trend for reciprocal recombination differences to be associated with change of interference values between adjacent intervals. A close association was found between reciprocal female recombination effects, male recombination and other component traits of hybrid dysgenesis. However, reciprocal differences in female recombination were not restricted to dysgenic crosses. Backcross experiments demonstrated that reciprocal differences in the centromeric region of chromosome III were the result of increased crossing-over in dysgenic F1 hybrids rather than decreased crossing-over in the reciprocal hybrids. It is concluded that genotype-cytoplasm interaction can be a major factor influencing recombination frequencies and that the use of interstrain hybrids for recombination measurement may lead to errors in the estimation of intrastrain frequencies.
Associations between allozyme loci and gene arrangements due to hitch-hiking effects of new inversions
Authors: Ishii K. , Charlesworth B.
Published: September 2009

This paper examines the hypothesis that the associations between alleles at allozyme loci and gene arrangements, which are observed in many Drosophila populations, result from inversions remaining associated with the alleles contained in the gametes in which they originally occurred. The effects of double crossing over in heterokaryotypes and of selection at loci linked to the allozyme loci, which are themselves assumed to be neutral, are studied theoretically. It is concluded that selection at linked loci is unlikely to have an important effect in retarding the decay of this type of association. The literature on associations between allozymes and gene arrangements is surveyed, and it is concluded that a ‘neutralist’ explanation of this sort cannot be excluded, except possibly in some cases where the allozyme locus is outside the inversion breakpoints and crosses over with measurable frequency in heterokaryotypes.
Sterile mutation inDrosophila melanogaster
Authors: Watanabe Takao K. , Lee Won Ho
Published: September 2009

The number of loci which are potentially able to produce sterility genes was estimated forDrosophila melanogaster. There appear to be, on the second chromosome, about 80 loci capable of producing male sterility and about 60 loci capable of producing female sterility. These figures seem to be considerably less than (400–500) loci responsible for lethal genes.
Digenic descent measures for finite populations
Authors: Cockerham C. Clark , Weir B. S.
Published: September 2009

The development of a set of two-locus descent measures is reviewed. The three digenic measures, inbreeding coefficient and parental and recombinant descent coefficients, are considered in detail. The derivations of these three in pedigrees, fixed mating systems, and random mating in monoecious or dioecious populations are given. General expressions for digenic frequencies and disequilibria functions at any time are found by applying the three digenic descent measures to two types of initial populations. The final or equilibrium status of the population is also given. As the inbreeding coefficient is the same as the recombinant descent coefficient in the case of complete linkage, avoidance or promotion of early inbreeding has similar effects on the two coefficients. Estimable components of linkage disequilibrium and other measures of association within and among populations are elaborated.
The basis for an apparent auxotrophy for reduced sulphur metabolites insF−mutants ofAspergillus nidulans
Authors: Arst Herbert N.
Published: September 2009

sF−mutants ofAspergillus nidulansare subject to toxicity by a metabolite derived from sulphate but are not blocked in cysteine biosynthesis. Bearing in mind the unavoidable presence of sulphate in agar-solidified media, their apparent auxotrophy for thiosulphate, L-cysteine or L-methionine stems from the ability of these reduced sulphur-containing metabolites to repress, directly or indirectly, the syntheses of sulphate permease and the enzymes of sulphate assimilation, thereby preventing synthesis of the toxic metabolite.
Genetic latitudinal adaptation ofDrosophila melanogaster: new discriminative biometrical traits between European and equatorial African populations
Authors: David J. , Bocquet C. , de Scheemaeker-Louis M.
Published: September 2009

Five biometrical traits (thorax length, wing length and width, sternopleural and abdominal chaetae numbers) were measured on 13 equatorial African strains and 30 French strains. In all cases highly significant differences were observed between the two geographic groups. These results are added to previously known variations concerning adult weight and ovariole number. In each place, the genetic particularities of the wild populations seem to be maintained by the selective pressure from environmental conditions, resulting in a homeostatic focusing of the best fitted average genotype. Analysis within each group showed that variations between strains were in most cases poorly or not correlated, so that partial or total genetic independence between the various traits measured seems likely.
Fine structure mapping and properties of mutations suppressing thelonmutation inEscherichia coliK-12 and B strains
Authors: Johnson Ben F.
Published: September 2009

Mutations,sulAandsulB, that suppress the UV sensitivity conferred by thelonmutation have been isolated and precisely positioned on the linkage map ofEscherichia coli. TheE. coliB strains Bs-3 and Bs-8 have been shown to possesssulAmutations. Also theE. coliK12 strain J6271 that possesses a suppressor of thelonmutation, previously designated assuf, has been shown to be asulAmutation. A series of methylmethane sulphonate resistant derivatives of anE. coliK12lonstrain has been isolated and genetically characterized. In addition tosulAmutations, a second suppressorsulBwas identified and located betweenleuandazigenes on the chromosome. NeithersulAorsulBmutations result in increased sensitivity to the antibiotics ampicillin, rifampicin, or actinomyein D, nor do they have any significant effect upon the overproduction of mucopolysaccharide caused by thelonmutation. Under some growth conditions thesulBmutation causes cells to be temperature sensitive for the cell division process at 42 °C.
Studies on male recombination in a Southern GreekDrosophila melanogasterpopulation
Authors: Yannopoulos George
Published: September 2009

A combined cytological and genetic analysis has been carried out to determine whether the spontaneous male recombination associated with a line ofDrosophila melanogasterderived from Southern Greece (31.1 MRF) involves chromosome breakage and random reunion. In all crosses showing male recombination, extensive abnormalities involving anaphase bridges and fragments were found at first and second meiotic divisions. This confirms that the low level of recombination associated with male recombination lines is not produced by normal, controlled crossing-over of the type found in females, but by chance reunions, following more erratic breakage events at first and second anaphase. In addition the occurrence of some limited premeiotic recombination cannot be excluded. The31.1 MRFsystem shows higher recombination levels at elevated temperatures (29 °C) and chromosome abnormality frequency is also greatly increased. The31.1 MRFinduces both male recombination and chromosomal abnormalities at meiosis when it is inherited from females deriving their cytoplasm from stock other thanCyL4/Pm. It is concluded that this factor acts independently of sex and that the reciprocal cross effect is caused by a cytoplasmic factor which the 31.1/CyL4strain inherited from theCyL4/Pmstock.
Polymorphism at the G6PD and 6PGD loci inDrosophila melanogaster
Authors: Bijlsma R.
Published: September 2009

The influence of sodium octanoate on the polymorphism at the loci G6PD and 6PGD inDrosophila melanogasterwas investigated by studying its effect on egg hatchability, larval-to-adult survival and adult survival. The results demonstrate the existence of differences in fitness between the different genotypes of the two loci both for larval-to-adult survival and for adult survival. Furthermore, changes in enzyme activity of both enzymes, brought about by the sodium octanoate treatment, were observed. This makes it highly probable that the observed differences in fitness can be ascribed to the loci themselves and not to linked fitness genes. Finally, this study demonstrates the existence of strong interaction between the two loci with respect to fitness. Epistasis was demonstrated both in the larval-to-adult survival experiment and in the adult survival experiment.
The time of detection of recessive visible genes in small populations
Authors: Robertson Alan
Published: September 2009

Homozygotes for recessive visible genes have often been discovered in lines under artificial selection, sometimes many generations from the start. As a help in the interpretation of this phenomenon, the distribution of the time to first detection as a homozygote of a recessive gene occurring only once in the initial generation has been obtained. Alternatively the results may be considered as referring to the time of first appearance as a homozygote of a new mutation occurring in a finite population. For a monoecious random mating population of size N with selfing permitted, the mean time to detection is very close to 2N⅓ over a range of N from 1 to 500 with a coefficient of variation of roughly 2/3 and a 95% upper limit about 2·5 times the mean. If selfing is prohibited, the mean time is increased by a little over 1 generation. The treatment is extended to cover the effects of artificial selection in favour of the heterozygote, of the frequency of occurrence in the initial generation and of the examination of more individuals each generation than are used as parents.
Mapping of the pneumococcus chromosome: differences between recipient strains varying inhexproperty and the location of theopt-r2gene
Authors: Butler L. O. , Nicholas G. , Grist R. W.
Published: September 2009

Transformation studies in pneumococcus had shown that loci determining the resistance to erythromycin and streptomycin were unlinked when strain Cl3 was recipient but linked when strain SIII-I was recipient. This phenomenon also applies to other pairs of markers studied in these two recipients, no matter whether the transforming DNA was derived from strain Cl3 or strain SIII-I. Other differences between the two recipient strains were also revealed. Whereas competent cultures of strain Cl3 were composed of all competent cells, which was in agreement with previous reports of pneumococcal cultures, strain SIII-I normally gave a maximum average of 28% competent cells. Strain SIII-I was unstable, since on repeated sub-culturing the competence peak profile changed and the value of ‘fcq’ increased. These properties were reflected in the twohex−strains 401 and R6x which were found to be similar to the ‘altered SIII-I’ strain. The results from the linkage studies have been applied to the chromosome map and have placed theopt-r2gene in thestr-r41-containing chromosome arm.
Comparing the means of inbred lines with the base population: a model with overdominant loci
Authors: Minvielle Francis
Published: September 2009

For one-, two- andn-locus models of a quantitative trait assumed to be determined by overdominant loci, it is shown that the mean of an inbred line will be equal to or larger than the mean of the base population if the original gene frequencies satisfy a condition which is generally a function of the degree of overdominance and of the genotypic values.
At-haplotype (tw75) overlapping two complementation groups
Authors: Artzt Karen , Babiarz Bruce , Bennett Dorothea
Published: September 2009

The recessive lethal T/t-complex haplotypetw75was isolated from Jena, East Germany, prior to 1973. It was at first thought to be a standard member of thetw5complementation group because matings ofT/tw75×T/tw5produced tailless offspring only (Dunn, Bennett & Cookingham, 1973). Cross tests with all other complementation groups and embryological studies have recently been completed, with results demonstrating thattw75does not complement the members of either thetw5or thetw1complementation groups. Histological studies show that compound embryostw75/tw5andtw75/tw1die with symptoms indistinguishable fromtw5/tw5andtw1/tw1homozygtes respectively. Thustw75represents the first confirmed isolation of at-haplotype that overlaps two complementation groups.
Variation forXchromosome expression in mice detected by electrophoresis of phosphoglycerate kinase
Authors: West John D. , Chapman Verne M.
Published: September 2009

The proportions of the two isozyme bands of the X-linked form of phosphoglycerate kinase (PGK-1) were compared in 16 tissues from four groups of adult heterozygous females. Little evidence was found for differences in expression of the two isozymes among tissues but there was a marked difference among the four groups of mice. The proportion of the PGK-1B enzyme was consistently lower in PGK-1AB heterozygous daughters of C3H/HeHa females than in corresponding heterozygotes with a C57BL/6Ha, DBA/2Ha or JBT/Jd mother. This difference was also observed in foetuses on the fourteenth day of gestation irrespective of whether the C3H/HeHaXchromosome was derived from the mother or the father. Sequential sampling of blood from the same heterozygous females provided no evidence for genetically determined cell selection in the adult erythropoietic tissue. The observed differences probably reflect variation at anX-chromosome controlling element locus among inbred strains of mice, similar to that described by Cattanach & Williams (1972) usingX-linked morphological markers, although this has yet to be tested.
The rate of mutant substitution in populations with overlapping generations
Authors: Pollak Edward
Published: September 2009

We consider an age-structured population that is observed at timest= 0, 1, 2,…. It is assumed that for eachtthere is the same number of individuals of a particular sex and age group. Another assumption we make is that an offspring of a specified sex has at all times the same probability of having a parent of a particular age and sex. It is shown that the rate of substitution of neutral mutants is/L, whereandLare respectively equal to the mean fraction of mutants among gametes succeeding in forming newborn individuals and the mean age of reproduction. This result also applies to monoecious populations. The substitution rate is also derived for advantageous mutants in a monoecious population. Once again, the mutation rate in the usual expression is replaced by/L. Implications of these results are discussed.
Studies of esterase 6 inDrosophila melanogaster: XI. Modification of esterase 6 activity by unlinked genes
Authors: Tepper Craig S. , Richmond Rollin C. , Terry Anne L. , Senior Alayne
Published: September 2009

The often remarkable similarity in structural gene products among related species has led to the hypothesis that species differences may reside largely in changes at regulatory gene loci. This hypothesis assumes that groups capable of speciating have allelic variation at regulatory loci in their natural populations. We have undertaken an analysis of the mode of regulation of theesterase 6(Est 6) locus inDrosophila melanogasterto determine the nature and extent of regulatory gene variation in natural populations. Analyses of esterase 6 (EST 6) activity among strains carrying the same thermostability variants reveal that significant, specific-activity differences are present. Reciprocal crosses between lines having high and low EST 6 activity show that loci other than theEst 6structural gene influence EST 6 activity. Analyses of male hybrids from crosses betweenD. melanogasterandsimulansindicate that theXchromosome of these flies affects the expression of theEst 6locus, resulting in unequal levels of enzyme activity from the two alleles. The effect is sex and tissue specific. Female hybrids carrying theXchromosomes of both species exhibit equal expression of the twoEst 6alleles. We have determined whether natural populations are polymorphic forXchromosomes which affect EST 6 activity by extracting singleXchromosomes from wild-collected males and placing these chromosomes in identical genetic backgrounds. Stocks which are otherwise genetically identical but carry independently derivedXchromosomes show significant differences in the activity of EST 6. These data suggest that regulatory loci may be commonly polymorphic in natural populations.
Predictions of response to artificial selection from new mutations
Authors: Hill William G.
Published: September 2009

The pattern of response expected from fixation of mutant genes for quantitative traits in finite populations is investigated for a range of distributions of mutant gene effects. The eventual rate depends on the total variance of mutant effects per generation, but the initial rate and the variance of response is higher if the distribution of mutant effects has a large standard deviation or is leptokurtic. The difference between initial and eventual rates of response is greater with large population sizes.

For a range of assumptions, new mutants are unlikely to have much influence on response for 20 or so generations, but then may contribute substantially, such that no plateaux are obtained. However, information on the variance contributed by mutants is almost entirely on bristle number inDrosophila.

It is argued that the role of new mutants should be considered in designing breeding programmes, in particular in utilizing large populations.
Genetics ofAspergillus flavus: complementation and mapping of aflatoxin mutants
Authors: Papa K. E.
Published: September 2009

Mutants ofAspergillus flavusimpaired in aflatoxin production were induced withN-methyl-N′-nitrosoguanidine and analysed by means of the parasexual cycle. The gene symbolaflwas assigned to this type of mutation. Diploid complementation tests revealed that most of 14aflmutants belonged to different complementation groups. One mutant (afl-1) failed to complement or only partially complemented all other mutants. Haploidization of one diploid revealed the independent segregation of twoaflmutants. Heterozygous diploids were synthesized between twoaflmutants and tester strains genetically labelled on eight linkage groups. Haploidization of the diploids led to the assignment of two aft mutants to linkage groups. Linkage ofafl-4 tow+andafl-1 toleuon linkage groups II and VII, respectively, was demonstrated.
The time of detection of sex-linked recessives in small populations
Authors: James J. W.
Published: September 2009

A sex-linked recessive gene with visible effect will first be detected in the hemizygous sex (male). In lines with equal numbers of males and females, when the gene is initially present in a single female the probabifity of detection falls from 2/3 in single pair lines to 0·54 in large lines. The mean and standard deviation of time to detection are almost independent of population size, being about 4/3 and 2/3 respectively. About 98% of all detections occur within three generations, so a gene detected much later than this after the foundation of a selection line is likely to be a new mutant. Higher initial frequencies and selection favouring heterozygotes increase the chance of detection. The time taken is decreased with higher initial frequencies and increased slightly by selection favouring heterozygotes.
Immunogenetics of an antigen identified in both sheep and cattle sera
Authors: De Benedictis Giovanna , Capalbo P. , Gallina E.
Published: September 2009

Alloimmunization in sheep revealed an antigen specificity B1 which is also to be found in cattle sera. The molecular weight of the protein carrying B1 was greater in sheep than in cattle, whilst in both cases its isoelectric point was at pH 6·2. The electrophoretic position of the antigen suggests that the molecule carrying B1 might be a β-globulin. Family studies indicated that in both species B1 was inherited in a simple Mendelian manner, as if it were a product of a dominant alleleB1at an autosomal locusB.
Isolation and characterization of a new class of amino-acid-analogue-resistant mutants inAspergillus nidulansusing reduced carbon flow
Authors: Singh Mahavir , Sinha Umakant
Published: September 2009

Four recessive amino-acid-analogue-resistant mutants were isolated on a medium containing acetate as the sole carbon source and the amino acid analogues p-fluorophenylalanine and ethionine. None of the mutants showed any growth requirement. Analysis of growth on media containing an amino acid as the sole nitrogen source indicated that two mutants out of the four possess normal systems for utilization of acidic, neutral, basic and aromatic amino acids. The mutantsfpa70 andfpa71 showed reduced growth on tryptophan as the sole source of nitrogen. Three new loci, identified after preliminary genetic analysis, were located on three linkage groups: one each on linkage groups I, VI and VIII.
Artificial induction of autogamy inParamecium caudatum
Authors: Tsukii Yuuji , Hiwatashi Koichi
Published: September 2009

Three methods of artificial induction of autogamy inParamecium caudatumwere described: (1) treatment with KCl+papain, (2) treatment with KCl and then with KCl + papain and (3) ordinary mating reaction and then treatment with papain. As expected, one-to-one segregation ratios were obtained in the progeny from the parents heterozygous for the two loci: mating type and lactate dehydrogenase. A high rate of autogamy is induced by method (1), but its use is restricted to only a few clones. Autogamy is also induced at a high rate by method (2), by which the induction is more stable. Autogamy is induced at a lower rate by method (3), but this method can be widely applied to every species ofParameciumwhich has complementary mating types. Some exautogamous progeny become completely sterile through successive autogamy. The cause of this sterility is discussed.
Genetic differences of DNA and RNA synthesis in the epithelium of the lens of the chick
Authors: Randall F. E. , Truman D. E. S. , Clayton R. M.
Published: September 2009

The genetically unrelated chick strains Hy-1 and Hy-2, which have been strongly selected for growth rate, both exhibit hyperplasia of the lens epithelium. These two strains and a control strain N, not selected for growth rate, were compared with respect to incorporation of3H-thymidine and14C-uridine by freshly excised lenses in culture at different times throughout a 24-h period. The levels of incorporation of label into the lens cells were found to vary according to the time of day. The pattern of diurnal variation in both thymidine and uridine incorporation was found to be strain specific. Hy-1 and Hy-2 showed a greater degree of synchrony than did normal (N) lenses, and the frequency of the peaks of incorporation was also higher. Autoradiography confirmed that only lens epithelium incorporates thymidine during culture and that the number of labelled nuclei depends on the time of day when the lenses were explanted. These data point to genetic control of the cell cycle.
Selection for ethanol tolerance andAdhallozymes in natural populations ofDrosophila melanogaster
Authors: Hickey D. A. , McLean Michael D.
Published: September 2009

Alcohol dehydrogenase (Adh) allozyme frequencies and tolerance of adult flies to ethanol were measured in population samples ofD. melanogasterfrom a winery in Southern Ontario. Samples were also tested from a number of non-winery sites.Adhfastfrequencies decrease as one moves away from the winery, but this drop in allozyme frequency is statistically significant only for those areas that are more than 3 km distant from the winery. Tolerance of adult flies to ethanol also differed between winery and non-winery populations, but these differences were not statistically significant. The data presented here may help to resolve the seeming conflict between the two previous studies ofAdhallozyme frequencies in natural populations from highand low-alcohol environments.
‘Overcompensation’ at an enzyme locus inDrosophila pseudoobscura
Authors: Toŝić Mirjana , Ayala Francisco J.
Published: September 2009

The experiments reported in this paper are primarily addressed to test the hypothesis of overcompensation; i.e. whether polymorphic populations exploit limiting environmental resources better than populations uniform for a single genotype. Overcomposition is an ecological consequence of some models of frequency-dependent selection. Secondarily, the experiments investigate whether overdominance exists at theMdh-2locus inDrosophila pseudoobscura.

Two types of experimental populations are established: ‘low-variability’ populations, in which all flies in a culture are offspring from only two laboratory strains; ‘high-variability’ populations, in which the flies in a culture are derived from 20 different strains. However, the overall degree of individual heterozygosity is the same in both types of populations. Three kinds of populations with respect to theMdh-2locus are established within each type; two are homozygous for either the100or the112allele, the third is heterozygous. A fourth kind of population exists among the high-variability populations; namely, populations in which all threeMdh-2genotypes are present. The experiments are done at two densities; one quasi-optimal, the other highly competitive.

Populations with high overall levels of genetic variation consistently produce more flies than low-variability populations. The differences are significant at the low, but not at the high, density. Moreover, populations polymorphic for theMdh-2locus generally produce more flies than populations having only oneMdh-2genotype. At high density, theMdh-2polymorphic populations have greater productivity than populations with anyone of the three genotypes, and the differences are statistically significant when the polymorphic populations are compared with either one of the two homozygotes or with the average of all three genotypes. In brief, overcompensatory effects – which may account for frequency-dependent selection – are observed in the experiment and may be a common phenomenon in nature.

Populations in which all individuals are heterozygous at theMdh-2locus produce in every case more flies than populations with only homozygotes for one or the other allele. The superiority of the heterozygotes is statistically significant for all comparisons at low density, but at high density it is statistically significant for the comparison with the homozygote rarer in nature and only in low variability populations.
On the nonautonomy of the small-kernel phenotype produced by B–A translocations in maize
Authors: Birchler James A.
Published: September 2009

Several of the B–A translocations of maize produce a small-kernel phenotype which is associated with hypoploid endosperms from fertilizations by sperm which result from nondisjunctional events of the B centromere at the second microspore division. Lin (1975) demonstrated that the small-kernel phenotype was not a consequence of the deficient nature of said endosperms, but involved a differential effect of male and female chromosomal regions.

The TB-A effect has been examined for evidence of autonomy in mosaics for the most extreme such case known, i.e. the small-kernel effect produced by the compound B–A translocation, 1La-5S8041. Although reduced-sized kernels are formed when the paternal contribution of the 1L-5S element is totally lacking from the endosperm, sectorial loss has no detrimental effect on dry weight. This phenomenon is therefore considered to be nonautonomous.
Protein variation and duplicate loci in the Atlantic salmon,Salmo solarL.
Authors: Cross T. F. , Ward R. D.
Published: September 2009

A natural population of Atlantic salmon,Salmo salarL. was screened for genetic variation at 59 protein loci, using a sample of parr, the juvenile freshwater stage. The mean heterozygosity per locus, estimated at 0·033 ± 0·014, is similar to that described in other salmonid species but low for fish species in general. Variation was observed at AAT, IDH, MD–ME, GLO, ADA, and SDH loci. The methods described should prove useful in stock discrimination and in producing salmon for restocking and sea-rearing. The observed extent of gene duplication is discussed in relation to the evolution and systematics of the salmonid fishes.
Population dynamics and the evolution of sex-determination in lemmings
Authors: Carothers A. D.
Published: September 2009

The hypothesis is advanced that the evolutionary stability of the unusual sex-determining mechanisms of the Wood Lemming (Myopus schisticolor) and of the Varying Lemming (Dicrostonyx torquatus) is a direct consequence of certain characteristic features of their population dynamics, and that these include phases of unrestrained population growth and of mass dispersal. Computer simulations confirm the feasibility of such an explanation. Predictions of this hypothesis are found to differ in a potentially testable manner from those of the ‘inbreeding’ hypothesis of Stenseth (1978). The demonstration of such a direct link between population ecology and evolutionary genetics would, if substantiated, be exceptional in mammals.
The detection of a recessive visible gene in finite populations
Authors: Karlin Samuel , Tavare Simon
Published: September 2009

Robertson, 1978, addressed the interesting problem of ascertaining the distribution of the time to detection of a recessive homozygote in a finite population. He was motivated in part by breeding and artificial selection practices. The same problem arises in the context of evolutionary processes and medical genetics since it refers to the time of first appearance as a homozygote of a new crossover event or a mutant gene.
Controlling elements in the mouse: IV. Evidence of non-randomX-inactivation
Authors: Johnston P. G. , Cattanach B. M.
Published: September 2009

The non-randomXchromosome expression that has been observed with coat markers in female mice heterozygous for theXcealleles,XceaandXceb, has now been investigated with the electrophoretic enzyme marker,Pgk-1. Because theXcestatus of thePgk-1amarked chromosome was not known, PGK expression was assessed inPgk-1a/Pgk-lbheterozygotes which carried eitherXceaorXcebon theirPgk-1bchromosome. The PGK-1A allozyme was found to predominate in both genotypes but whenXcebwas present on thePgk-lbchromosome the expression of the two allo-zymes was less unequal. This effect was seen in both liver and kidney of adults and to at least the same degree in embryos aged 13·5 and 7·5 days. The results have been interpreted to mean that the non-randomXexpression derives from a primary non-randomness of theXinactivation process and that a new and more extremeXceallele, designatedXcec, was present on thePgr-1a-markedXchromosome.
Controlling elements in the mouse: V. Linkage tests with X-linked genes
Authors: Cattanach B. M. , Papworth D.
Published: September 2009

Previous studies have shown that the mouseXchromosomal locus,Xce, which causes non-randomXchromosome inactivation, is closely linked to the Is(X; 7)CtX-autosome translocation. This has placed it either nearTaon one side of the breakpoint or nearjpon the other. Linkage tests withMovbrandTanow demonstrate that the locus in fact lies close toTa. The data also provide genetic evidence which establish that the C3H/HeHXchromosome carries theXceaallele of this gene and the JU/FaCt and C57BL/GoHXchromosomes carry theXceballele, and further suggest that theX-linked modification of the heterozygous phenotypes ofX-linked genes observed by various other investigators are all attributable to differences at theXcelocus. Evidence of a maternal influence uponMovbrphenotypes is also presented. This appears to operate independently of theX-inactivation process, probably through an effect of differing levels of copper in the milk in early life upon the mutant coat colour in the young.
The distribution of heterozygosity in temperate and tropical species ofDrosophila
Authors: Latter B. D. H.
Published: September 2009

Electrophoretic surveys for nine species ofDrosophilahave been summarized in terms of the relative contribution to heterozygosity of each of ten gene frequency classes, the mean frequency of heterozygotes within subpopulations, and the degree of genetic divergence between subpopulations. It has been shown that the neutral model proposed by Kimura, and modified by Ohta to include the accumulation of slightly disadvantageous mutations, is capable of explaining all features of the data. The consistent difference between group I and group II enzymes can be explained by a difference in the average intensity of selection against mutational variants in the two groups. A highly significant difference between the temperate and tropical species in the distribution of heterozygosity appears to be due to the smaller effective breeding population sizes in the case of the temperate species.
Multilocus nonrandom associations inDrosophila melanogaster
Authors: Malpica J. M. , Briscoe D. A.
Published: September 2009

Seven third chromosome samples from laboratory populations and one from a wild population were classified by their genotypes at five allozyme loci and by the occurrence of lethals. The data were analysed for independence among classifications by a randomization method, and it was found that when the number of classifications is high the independence hypothesis does not hold. We have split the independence hypothesis among populations and have found that the lack of fit to the hypothesis comes mainly from the wild population. As one of our classifications was lethality, these findings seriously question the interpretation of multilocus fitness estimations. To split the independence hypothesis into interactions, the criterion of Bartlett for non-interaction with exact probability methods was used; interactions at the levels of pairs and triplets were not significant as a whole. It was not possible to carry the interaction analysis any further as the frequencies of chromosomal types were completely determined by their marginal totals at orders of interaction higher than that of triplets. Available parametric estimations of these high order interactions are therefore of dubious meaning. The analyses of chromosome samples and the temporal surveys of population cages described here, as well as data from the literature, suggest that the Est 6-Pgm region is prone to show disequilibrium.
Lethality of heterozygotes betweent-haplotype complementation groups of mouse: sex-related effect on lethality oft6/tw5heterozygotes
Authors: Bechtol Kathleen B.
Published: September 2009

The various lethalt-haplotypes are divided into several complementation groups defined by lethality oftx/tyheterozygotes, and only partial complementation is usually observed in heterozygotes betweentcomplementation groups. Several effects of thetregion have been found to be preferentially or exclusively detectable in males. This paper describes results showing that the viability oft6/tw5heterozygotes is influenced by the sex of the embryo; female viability is only slightly reduced (viability ratio approximately 0·80), while male viability is far below normal (0·25).
Identification of the chromosomes involved in a wheat-rye translocation using isozyme markers
Authors: Rao I. Narayana , Rao M. V. Prabhakara
Published: September 2009

Monosomic and disomic substitutions of Imperial rye chromosome C for 4A of Chinese Spring wheat were analysed for two enzyme markers, alcohol dehydrogenase (ADH) and 6-phosphogluconate dehydrogenase (6-PGD). The gene(s) coding for ADH and 6-PGD were located on the short and long arms of rye chromosome C respectively.

Isozyme analyses revealed that the substitute chromosome was a translocation involving alpha arm of wheat chromosome 4A and long arm of rye chromosome C. Pairing behaviour of the substitute chromosome with rye and wheat chromosomes in hybrids with rye addition line C and ditelosomic 4A (alpha) confirmed this.
The structure of hair and follicles of mice carrying the naked (N) gene
Authors: Raphael Kathryn A. , Chapman R. E. , Frith Penelope A. , Pennycuik Pamela R.
Published: September 2009

The hairs and follicles from mice carrying the naked (N) gene have been examined using both scanning and transmission electron microscopy in addition to light microscopy. Fibre cuticle cells and occasionally cortical cells were absent from the follicles of N / + mice when the base of the hair was growing. In N / N follicles there was a frequent lack of both cuticle and cortical cells throughout the growth phase of the follicles. Abnormalities were also observed in the manner in which the synthesized keratin was deposited in the fibres. The possible mode of action of the N gene is discussed in the light of these results.