bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetic studies of D-alanine-dehydrogenase-less mutants ofEscherichia coliK12
Authors: Franklin F. C. H. , Venables W. A. , Wijsman H. J. W.
Published: September 2009

Genetic analysis of 12 mutants ofEscherichia coliK12 defective in D-alanine dehydrogenase showed thatalnAanddadare alternative names for the same locus.dadwas shown to be a single gene which codes for a protein of 55000–60000 mol. wt. Study of thermosensitive mutants ofdadindicated that its product is a structural component of D-alanine dehydrogenase. The regulatory genealnRwas shown to be involved in positive control ofdadexpression. This was concluded from (i) the absence of constitutive strains among Dad+revertants ofalnR–mutations, (ii) thetransdominance ofalnR+toalnR–, and (iii) the failure to isolate fully constitutive strains by any means. To obtain a uniform nomenclature it is proposed to re-namedadasdadBandalnRasdadQ.
Estimation of effective population size from data on linkage disequilibrium
Authors: Hill William G.
Published: September 2009

A method is proposed for estimating effective population size (N) from data on linkage disequilibrium among neutral genes at several polymorphic loci or restriction sites. The efficiency of the method increases with larger sample size and more tightly linked genes; but for very tightly linked genes estimates ofNare more dependent on long-term than on recent population history. Two sets of data are analysed as examples.
Mitochondrial mutagenesis inSaccharomyces cerevisiae: the origin ofmit−mutants
Authors: Putrament Aleksandra , Ejchart Anna
Published: September 2009

Yeast cells contain many copies of mitochondrial (mit) genomes. The question we tried to answer was howmit−mutations occurring in one genome as a result of mutagenic treatment might yield homoplasmic mutant cells. Three processes were considered. First, that these cells originate by segregation of mutant and standard alleles during cell division. Secondly, that they originate through intracellular selection, for which cell division is not required. Thirdly, that recombination involving the mutant and standard alleles is non-reciprocal and unidirectionalmit+→mit−so that the mutant allele is spread into the entire population of mitochondrial genomes within a cell, thus making it homoplasmicmit−. The results indicate that the first process, although efficiently producing homoplasmic cells from heteroplasmic zygotes (for review see Birky, 1978), seems to play only a minor, if any, role in producing homoplasmic mutant progenies from mutagenized cells. The most important is the second process, that is, intracellular selection occurring in cells which have one or a few genomes carryingmit−mutations, while the remaining genomes are irreversibly damaged. The third process, unidirectionalmit+→mit−conversion, does not seem to play any part.
The susceptibility to cortisone-induced cleft palate of recombinant inbred strains of mice: lack of association with theH-2haplotype
Authors: Vekemans M. , Taylor B. A. , Fraser F. C.
Published: September 2009

Recombinant-inbred (RI) strains of mice derived from the cross of strains C57BL/6J and DBA/2J were used to study the inheritance of susceptibility to cortisone-induced cleft palate. Most of the RI strains could be classified as either resistant, like C57BL/6J, or susceptible, like DBA/2J, suggesting the segregation of a major locus. An association with the phosphoglucomutase-1 locus (Pgm-1) on Chromosome 5 was observed. There was no association with the H-2 locus on Chromosome 17 as had been reported in previous studies utilizing different strains. We conclude that susceptibility to cortisone-induced cleft palate may be determined by different loci depending on the strains studied.
Copper localization in the duodenal mucosa of heterozygous tortoiseshell (Moto/+) female mice (Mus musculus)
Authors: Sheedlo Harold J. , Beck Melvin L.
Published: September 2009

The duodenal mucosa of normal (+/+) and heterozygous tortoiseshell (Moto / +) female mice was analysed by an ultrastructural histochemical copper localization technique. Copper was rarely detected along the duodenal microvilli of + / + female mice. However, copper was localized on the surface of the brush border of the duodenal mucosa and within pinocytotic vesicles at the base of the microvilli of Moto /+ female mice. The mottled defect may involve a defective intestinal uptake of copper, as well as a faulty copper transport mechanism.
Nucleotide sequences of highly repeated DNAs; compilation and comments
Authors: Miklos George L. Gabor , Gill Amanda Clare
Published: September 2009

The nucleotide sequence data from highly repeated DNAs of inverte-brates and mammals are summarized and briefly discussed. Very similar conclusions can be drawn from the two data bases. Sequence complexities can vary from 2 bp to at least 359 bp in invertebrates and from 3 bp to at least 2350 bp in mammals. The larger sequences may or may not exhibit a substructure. Significant sequence variation occurs for any given repeated array within a species, but the sources of this heterogeneity have not been systematically partitioned. The types of alterations in a basic repeating unit can involve base changes as well as deletions or additions which can vary from 1 bp to at least 98 bp in length. These changes indicate that sequenceper seis unlikely to be under significant biological constraints and may sensibly be examined by analogy to Kimura's neutral theory for allelic variation. It is not possible with the present evidence to discriminate between the roles ofneutralandselectivemechanisms in the evolution of highly repeated DNA.

Tandemly repeated arrays are constantly subjected to cycles of amplification and deletion by mechanisms for which the available data stem largely from ribosomal genes. It is a matter of conjecture whether the solutions to the mechanistic puzzles involved in amplification or rapid redeployment of satellite sequences throughout a genome will necessarily give any insight into biological functions.

The lack of significant somatic effects when the satellite DNA content of a genome is significantly perturbed indicates that the hunt for specific functions at thecellularlevel is unlikely to prove profitable.

The presence or in some cases theamountof satellite DNA on a chromosome, however, can have significant effects in the germ line. There the data show that localized condensed chromatin, rich in satellite DNA, can have the effect of rendering adjacent euchromatic regionsrec−, or of altering levels of recombination on different chromosomes. No data stemming from natural populations however are yet available to tell us if these effects are of adaptive or evolutionary significance.
Aberrant segregation patterns and gene mappability inAscobolus immersus
Authors: Leblon G. , Haedens V. , Kalogeropoulos A. , Paquette N. , Rossignol J.-L.
Published: September 2009

Crosses between various types of mutant giving specific patterns of aberrant segregation were performed in theb2spore colour locus ofAscobolus immersus. The map of 41 mutations showing various patterns of aberrant segregation was established. The frequency of wild-type recombinants and the map additivity, map expansion and map contraction characteristics were shown to be strongly dependent upon the pattern of aberrant segregation of the mutations used. Mutations giving no postmeiotic segregation and an excess of conversion to wild type over conversion to mutant exhibit map expansion in small intervals and a strong map contraction in large intervals. Mutations giving postmeiotic segregations also exhibit map contraction in large intervals. Mutations giving no postmeiotic segregations and an excess of conversion to mutant over conversion to wild type show map additivity and thus provide a simple way for devising gene maps. The relationship between the mapping properties and the pattern of aberrant segregations is accounted for when considering parameters of gene conversion: frequency and distribution of hybrid DNA, frequency and direction of mismatch correction.
The cytogenetic boundaries of the rDNA region within heterochromatin of theXchromosome ofDrosophila melanogasterand their relation to male meiotic pairing sites
Authors: Appels R. , Hilliker A. J.
Published: September 2009

The proximal breakpoints of the inversion chromosomesIn(1)ωm4andIn(1)m51bwere shown, byin situhybridization, to define the boundaries of the ribosomal DNA region located within theXchromosome heterochromatin (Xh). We estimate thatat least95% of the rDNA is located between theIn(1)ωm4andIn(1)ωm51bproximal breakpoints. In contrast only 60–70% of the Type I intervening sequences located inXhare located between these breakpoints. The Type I intervening sequences in the rDNA region occur as inserts in the 28S rRNA sequences while the remainder of the sequences are distal to theIn(1)ωm4breakpoint and not associated with rRNA genes.

The regions of Xh which contain rDNA and Type I intervening sequences were related to regions shown by Cooper (1964) to contribute to meiotic pairing between theXandYchromosomes in male Drosophila. We demonstrate that the rRNA coding region contributes toX/Ypairing. However, no single region of Xh is required for fidelity of male meiotic pairing of the sex chromosomes.
Path analysis under generalized assortative mating: II. American I.Q.
Authors: Rao D. C. , Morton N. E. , Lalouel J. M. , Lew R.
Published: September 2009

Rice, Cloninger & Reich (1980) showed that correlational data on American I.Q. is consistent with a rather low genetic heritability. Here we confirm their general results with a more parsimonious model. From phenotypic data alone, the estimates of genetic and cultural heritability are 0·31 and 0·42, respectively. Using environmental indices, the parsimonious estimates become 0·34 and 0·26, respectively.
Non-selfing mutants from selfing (Het−) strains ofPhysarum polycephalum
Authors: Honey N. K. , Poulter R. T. M. , Aston R. J.
Published: September 2009

Plasmodial formation in the MyxomycetePhysarum polycephalumis under heterothallic control by a mating type (mt) locus. In natural isolates only amoebae with differentmtalleles are able to cross to form diploid plasmodia. A class of mutants isolated from heterothallic amoebae, together with the variant strainCL, is able to form plasmodia in pure clones, designated as selfing. Non-selfing mutants have been isolated fromCLand from other selfing amoebae.

This paper reports the isolation and analysis of 64 non-selfing derivatives (designated Npf−) from seven selfing (Het−) strains. The Npf−mutants could be grouped into eight classes on the basis of their crossing and complementation patterns. The possible significance of these mutants is discussed.
Genetic differentiation of quantitative characters between populations or species: I. Mutation and random genetic drift
Authors: Chakraborty Ranajit , Nei Masatoshi
Published: September 2009

Introducing a new genetic model called the discrete allelic-state model, the evolutionary change of genetic variation of quantitative characters within and between populations is studied under the assumption of no selection. This model allows us to study the effects of mutation and random genetic drift in detail. It is shown that when the allelic effects on phenotype are additive, the rate of approach of the genetic variance within populations to the equilibrium value depends only on the effective population size. It is also shown that the distribution of genotypic value often deviates from normality particularly when the effective population size and the number of loci concerned are small. On the other hand, the interpopulational variance increases linearly with time, if the intrapopu-lational variance remains constant. Therefore, the ratio of interpopulational variance to intrapopulational variance can be used for testing the hypothesis of neutral evolution of quantitative characters.
A new allele sash (Wsh) at theW-locus and a spontaneous recessive lethal in mice
Authors: Lyon Mary F. , Glenister P. H.
Published: September 2009

A mutation to an apparently new allele at theW-locus of the mouse arose spontaneously in a cross between two inbred strains. Heterozygotes have a broad white sash, leading to the name and symbol sash,Wsh. Homozygotes are black-eyed whites which are viable, fertile and not anaemic, although the gene does cause mild haematopoietic defects. The original mutant animal also carried a spontaneous recessive lethal mutation on chromosome 5, mapping at 2 cM distal to theW-locus.
Genetic fine-structure of theGA-1locus in the higher plantArabidopsis thaliana(L.) Heynh
Authors: Koornneef M. , Van Eden J. , Hanhart C. J. , De Jongh A. M. M.
Published: September 2009

Non-germinating gibberellin (GA) responsive mutants are a powerful tool to study genetic fine structure in higher plants. Nine alleles (EMS-and fast neutron-induced) of thega-1locus ofArabidopsis thalianawere tested in a complete half-diallel. No wild type ‘recombinants’ were found in the selfed progeny of 9 homoallelic combinations (in total 3 × 105plants); in the progenies from the 36 selfed hetero allelics the wild type frequency ranged from zero to 6·6 × 10−4. These frequencies allowed the construction of an internally consistent map for five different sites representing eight alleles. The ninth allele covered three sites and thus behaved like an intragenic deletion. The estimate of the total genetic length of thega-1locus was 0·07 cM. The order of the sites was also clearly reflected by the association with proximal outside markers. On the assumption that wild type gametes predominantly arise from reciprocal events, it was shown that a cross-over within thega-1locus leads to positive interference in the adjacent region.

The results are discussed with respect to the mutagen used, the frequencies found in other plant and Drosophila genes, and the possible occurrence of gene conversion.
X-chromosome segregation, maternal age and aneuploidy in the XO mouse
Authors: Brook J. D.
Published: September 2009

Cytogenetic studies have ascertained that the segregation of the X-chromosome, during the first meiotic division of the oocyte in XO mice, occurs at random, contrary to the finding of some earlier authors. The ratio of nullo-X to X-bearing oocytes at ovulation does not change with maternal age. The usefulness of the XO mouse as a model for aneuploidy production in women (Lyon & Hawker, 1973) is discussed.
Transposon-Directed Mutagenesis and Chromosome Mobilization in Acinetobacter calcoaceticus EBF65/65
Authors: Towner K. J.
Published: September 2009

RP4::Mu was used to insert Tn3171 into the Acinetobacter calcoaceticus EBF65/65 chromosome. Insertions occurred at a frequency of approximately 10−7 per recipient cell. Auxotrophic mutations resulted from 28% of the Tn3171 insertions examined, with a possible ‘hot-spot’ for insertion in a gene for arginine biosynthesis. The frequency of subsequent precise excision of Tn3171 from the chromosome was less than 10−10. When attempts were made using RP4 derivatives to mobilize the chromosome from a strain containing an arg::Tn3171 insertion, it was found that the enhanced transfer frequency of the adjacent region of the chromosome was dependent on the original Tn3171 insertion, but was independent of the presence of Tn3171 on the mobilizing plasmid.
Genetic variation of wild mouse populations in southern Germany: II. Serological study
Authors: Figueroa Felipe , Zaleska-Rutczynska Zofia , Adolph Sabine , Nadeau Joseph H. , Klein Jan
Published: September 2009

A total of 207 wild mice trapped at different localities in southern Germany were tested for the presence of antigenic determinants controlled by class I genes (KandD) of theH-2complex. The test was based on the complement-dependent killing of lymphocytes in the micro-cytotoxicity assay. Both private (allele-specific) and public (shared) determinants were tested using polyclonal and monoclonal antibodies. The results of the H-2 typing were in agreement with karyological typing which divided the sampled mice into 5 populations. Each population was characterized by a certain antigenic profile (occurrence of individual determinants at certain frequencies); the profiles of the individual populations were sufficiently unique to differentiate these populations but at the same time sufficiently similar to indicate common origin of the populations. The karyological typing of the same mice reveals that all 5 populations share 1 pair of metacentric chromosomes,Rb(4.12)1Tu, but that, in addition, each population has at least one metacentric chromosome differentiating it from other populations. We interpret these findings as evidence that all wild mice in southern Germany stem from a common stock in which theRb(4.12)1Tutranslocation became fixed and which subsequently differentiated into the individual populations. This differentiation is accompanied by the fixation of new Robertsonian translocations (different ones in different populations) and the acquisition of characteristic H-2 antigenic profiles.
An investigation into the origins of meiotic aneuploidy using ascus analysis
Authors: Fulton A. M. , Bond D. J.
Published: September 2009

Aneuploidy can result from a variety of defects at meiosis. Results are presented of crosses ofSordaria brevicollisin which aneuploid spores are detected through complementation of spore colour mutants at thebufforgrey-6 loci on linkage groups II and IV respectively. By using ascus analysis, the underlying cause of the aneuploidy can be deduced in many cases. Thus non-conjuction (pairing failure) and non-disjunction at the first meiotic division, premature centromere division, non-disjunction at the second division, and pre-meiotic errors such as extra replication of the chromosomes can be distinguished. Both linkage groups were found to give a similar proportion of the different errors. Non-conjunction and first-division non-disjunction formed 60–70% of detectable cases, whilst premature centromere division and second-division non-disjunction comprised 10% and 5% of aneuploids respectively. However, only a small proportion of second-division errors are detected.

It is proposed that the systems described in this paper can form the basis of a valuable screening method for detecting agents which increase aneuploid frequency. The advantages and disadvantages of using lower eukaryotes in this way are discussed.
Chromosomal locations of elevenElytrigia elongata(=Agropyron elongatum) isozyme structural genes
Authors: Hart Gary E. , Tuleen Neal A.
Published: September 2009

The zymogram phenotypes of 11 enzymes were determined for 22Triticum aestivumcv. Chinese Spring-Elytrigia elongatadisomic and ditelosomic chromosome addition lines. Eleven isozyme structural genes were located in specific arms of sixE. elongatachromosomes, as follows:Gpi-E1in 1ES,Est-E1in 3ES,Got-E3in 3EL,Adh-E1andLpx-E1in 4ES,Adh-E2andLpx-E2in 5EL,Amp-E1in 6Eα,Adh-E3andGot-E2in 6Eβ, andEp-E1in 7EL. TheE. elongatachromosomes present in five disomic addition lines have previously been designated 1E, 2E, 4E, 6E, and 7E to indicate their homoeology with Chinese Spring chromosomes. The results of this study support these designations. The development of disomic putative 3E and 5E addition lines is reported. The added chromosomes designated IV, V, and VI that are present in three of the seven original disomicT. aestivum-E. elongataaddition lines are translocated. Evidence that VL and VIL are opposite arms of 2E and that IV is partially homoeologous to 3E has been published. The results reported in this paper indicate that IVS = 3ES, IVL = 7EL, VS = 3ES, and VIS = 5ES and are consistent with VL and VIL being opposite arms of 2E. The synteny relationships of the 11E. elongataisozyme genes identified in this study are fully consistent with those of homoeologousT. aestivumcv. Chinese Spring genes and thus provide evidence that the gene synteny groups which these two species inherited from their common ancestor are conserved. This study further documents the valuable role that studies of isozyme genes can play in the isolation, characterization, and maintenance of alien chromosomes, telosomes, and chromosomal segments in wheat strains.
Macrogeographic genetic variation in a human commensal:Aedes aegypti, the yellow fever mosquito
Authors: Wallis Graham P. , Tabachnick Walter J. , Powell Jeffrey R.
Published: September 2009

Genetic variation at 11 enzyme loci inAedes aegyptipopulations collected from 63 localities around the world is presented. A UPGMA tree based on genetic distance values clusters populations of sylvanA. aegypti formosusfrom West Africa and East Africa together, along with Asian and south-eastern U.S. populations. DomesticA. aegypti aegyptifrom East Africa and all other New World populations form the other major cluster. Multivariate discriminant analysis allows recognition of seven major global ‘genetic–geographic’ groups, which are consistent with the genetic distance data. Populations from the south-eastern U.S. are clearly genetically distinct from other U.S. and Mexican populations. This distinct gene pool may be indicative of reinfestation of areas whereA. aegyptiappears to have been absent in the recent past. Other evolutionary and epidemiological implications of the genetic population structure ofAedes aegyptiare discussed.
Biochemical genetics of Neurospora nuclease II: Mutagen sensitivity and other characteristics of the nuclease mutants
Authors: Mishra N. C. , Forsthoefel A. M.
Published: September 2009

Five newnucmutants ofNeurospora crassawere characterized for their relative sensitivities to different mutagens (UV, MNG, MMS), to mitomycin-C and to histidine; latter has been shown to inhibit the growth of certain UV sensitive mutants. These mutants were also compared for their capabilities for spontaneous mutation as determined by resistance to p-fluoro-phenylalanine. Based on these characterization, the mutants seem to belong to two groups. The first group includednuc-3andnuc-6which showed sensitivity to all mutagen tested and possessed capability for a very high frequency of spontaneous mutation (i.e. mutator effect). The second group includednuc-4, nuc-5andnuc-7; these were as resistant to different mutagens as the wild type strain, but possessed an antimutator effect (i.e. the frequency of spontaneous mutation by these three mutants were at least 0·5–100 × less than the wild type strains). There was some variation in these properties of mutants belonging to the two groups. Among all the fivenucmutants,nuc-3was characterized by extreme sensitivity to all mutagens. None of the fivenucmutants were sensitive to histidine. The properties ofnucmutants are discussed in relation to their possible role in DNA repair and recombination.
The population dynamics of transposable elements
Authors: Charlesworth Brian , Charlesworth Deborah
Published: September 2009

This paper describes analytical and simulation models of the population dynamics of transposable elements in randomly mating populations. The models assume a finite number of chromosomal sites that are occupable by members of a given family of elements. Element frequencies can change as a result of replicative transposition, loss of elements from occupied sites, selection on copy number per individual, and genetic drift. It is shown that, in an infinite population, an equilibrium can be set up such that not all sites in all individuals are occupied, allowing variation between individuals in both copy number and identity of occupied sites, as has been observed for several element families inDrosophila melanogaster. Such an equilibrium requires either regulation of transposition rate in response to copy number per genome, a sufficiently strongly downwardly curved dependence of individual fitness on copy number, or both. The probability distributions of element frequencies, generated by the effects of finite population size, are derived on the assumption of independence between different loci, and compared with simulation results. Despite some discrepancies due to violation of the independence assumption, the general pattern seen in the simulations agrees quite well with theory.

Data fromDrosophilapopulation studies are compared with the theoretical models, and methods of estimating the relevant parameters are discussed.
Changes in genetic constitution and sterol composition during growth of nystatin-resistant heterokaryons ofNeurospora crassa
Authors: Ogden Jill E. , Grindle Morris
Published: September 2009

Heterokaryons ofN. crassawere synthesized from homokaryotic strains differing in sterol composition and sensitivity to the polyene antibiotic nystatin. Mycelia of the nystatin-sensitive strainerg-1+contained ergosterol and episterol, and the nystatin-resistant mutanterg-1 contained fecosterol and lichesterol. Mycelia of heterokaryons with different proportions oferg-1+:erg-1 nuclei contained various proportions of the four sterols. Ergosterol was the principal sterol in heterokaryons with more than 5%erg-1+nuclei.

Heterokaryons with various proportions oferg-1+:erg-1 nuclei were grown for several weeks along tubes of synthetic media. Growth rates were stable on minimal medium and nutritionally supplemented media but nuclear proportions often fluctuated. Growth rates fell sharply on nystatin-supplemented media and there were adaptive increases in proportions of mutanterg-1 nuclei which resulted in selection of nystatin-resistant homokaryotic mycelia.
Bar reversion and hybrid dysgenesis inDrosophila melanogaster:reversion in males and in inversions
Authors: Colgan D. J.
Published: September 2009

The effect of the P-M system of hybrid dysgenesis inDrosophila melanogasteron unequal crossing-over was studied using the Bar duplication. This system of dysgenesis had no demonstrable effect on the rate of Bar reversion. In the course of the study it was found that there was a greatly reduced rate of reversion in two homozygous inversion stocks. Further, one revertant was found which may result from unequal crossing over at the Bar locus in males.
The Cincinnati Lipid Research Clinic family study: Bivariate path analyses of lipoprotein concentrations
Authors: McGue M. , Rao D. C. , Reich T. , Laskarzewski P. , Glueck C. J. , Russell J. M.
Published: September 2009

Methods for the analysis of the joint transmission of two phenotypes are described and used to determine the extent to which lipoprotein concentrations share a common genetic and/or environmental background. Analysis of data on 160 Caucasian nuclear families revealed that the observed phenotypic association between high-density cholesterol (HDL) and low-density cholesterol (LDL) could be accounted for in terms of common family environmental effects alone (estimated genetic correlation, ρG = −0·132±0·136; estimated residual environmental correlation, ρR = 0·065±0·230). The association between HDL and very-low-density cholesterol (VLDL) could not be accounted for in terms of family environmental effects alone. For HDL and VLDL the residual environmental correlation was significant while the genetic correlation was not (ρG = −0·111±0·214, ρR = −0·421±0·172). The correlation between LDL and VLDL also could not be accounted for in terms of common family environmental effects alone, although here a genetic relationship appears to be the important factor (ρG = 0·330±0·192, ρR = 0·010±0·217).
The number of loci affecting a quantitative trait in Drosophila melanogaster revealed by artificial selection
Authors: Gallego Araceli , López-Fanjul Carlos
Published: September 2009

Individual and within-full-sib family selection for low sternopleural bristle number was carried out for 17 generations, with six replicate lines for each selection method. Our results can be summarized as follows: (1) the response to selection was exhausted very quickly, (2) the additive variance of the selected lines declined rapidly, (3) the variation in response to selection decreased as selection progressed, (4) genetic differences among replicates at the selection limit were small, (5) individual selection resulted in a higher initial response than within-family selection, but similar limits were achieved with both procedures. These observations are consistent with the hypothesis that the pattern of response to selection is due to the segregation in the base population of only a few loci with large effects, at intermediate frequencies.
Contrasted, a steel allele in the mouse with intermediate effects
Authors: Beechey C. V. , Searle A. G.
Published: September 2009

The steel allele, contrasted (Slcon), arose in a neutron irradiation experiment.Slconis fully penetrant and heterozygotes can be recognized at or soon after birth by darkly pigmented external genitalia in both sexes, while the adult coat tends to be a little lighter than normal. Homozygotes also have dark genitalia and a markedly diluted coat. Both eumelanin and phaeomelanin are affected, with reduced numbers of cortical and medullary pigment granules in the hairs. Contrasted also affects the haematopoietic system, causing slight macrocytic anaemia in the homozygote.Slconhomozygous males are fertile but testes weigh on average 20% less than in their heterozygous litter-mates. Homozygous females are usually sterile although if mated early (4½−6 weeks) they occasionally have a single litter. Ovarian sections showed a gradual degeneration of oocytes in Graafian follicles so that most had gone by 2 months. Similarly, vaginal smears indicated that after about three normal cycles homozygous females lapsed into a state of persistent dioestrus; injections with gonadotrophins did not prolong their period of fertility or cause a resumption of their oestrous cycles. The effects on fertility, pigmentation and haematology of contrasted when combined with other steel alleles are also described.
Variance component analysis for viability in an isolated population ofDrosophila melanogaster
Authors: Tachida Hidenori , Matsuda Muneo , Kusakabe Shin-Ichi , Mukai Terumi
Published: September 2009

Using the 602 second chromosome lines extracted from the Ishigakijima population ofDrosophila melanogasterin Japan, partial diallel cross experiments (Design II of Comstock & Robinson, 1952) were carried out, and the additive genetic variance and the dominance variance of viability were estimated. The estimated value of the additive genetic variance is 0·01754±0·00608, and the dominance variance 0·00151±0·00114, using a logarithmic scale. Since the value of the additive genetic variance is much larger than expected under mutation–selection balance although the dominance variance is compatible with it, we speculate that in the Ishigakijima population some type of balancing selection must be operating to maintain the genetic variability with respect to viability at a minority of loci. As candidates for such selection, overdominance, frequency-dependent selection, and diversifying selection are considered, and it is suggested that diversifying selection is the most probable candidate for increasing the additive genetic variance.
Population genetics of extranuclear genomes under the neutral mutation hypothesis
Authors: Takahata Naoyuki
Published: September 2009

Population genetics of extranuclear genomes is further developed under the neutral-mutation random-drift hypothesis, and the characteristic evolutionary aspects are summarized. Several formulae derived here are concerned with the variances of genetic variability (gene identity) at a single extranuclear locus and the evolutionary distance between two isolated populations which is estimated from a comparison of homologous linked nucleotide sites. Two types of variance are considered; one is the variance in the entire population (VQ) and the other is the variance within a single germ cell (VH). When compared with a Mendelian genetic system in a panmictic population, an extranuclear genetic system has the following equilibrium properties: (1) the mean genetic variability is low if, despite the high multiplicity of the genome in a cell, the proportion of the cytoplasmic contribution from the male's gamete is small, (2) the effect of recombination is small and a large amount of variance of linkage disequilibrium tends to be maintained, (3) the overall relationship between the mean and variance of genetic variability does not much differ butVQ(VH) is expected to be small if the paternal contribution is small, and (4) the evolutionary distance estimated depends on the extent of intrapopulational variation in a common ancestor population which in turn depends on within-cell variation. I argue that there is an analogy between the model of extranuclear genomes in a finite population and that of nuclear genes in a subdivided population. The analogy helps our understanding of some properties in an extranuclear genetic system.
Evolutionary dynamics of extranuclear genes
Authors: Takahata N. , Slatkin M.
Published: September 2009

We studied the evolutionary dynamics of extranuclear genes taking into account simple kinds of selection, two modes of inheritance and the multiplicity of genomes within a cell. Particular attention was paid to the accumulation of advantageous or deleterious mutations in an extranuclear genome. Within-generation drift due to multiplicity of genome and non-Mendelian segregation promotes the fixation of advantageous mutations and prevents deleterious mutations from accumulating. We show also that the extent of paternal contribution makes little difference in the rate, but, in contrast, the configuration of the genome and the mode of transmission both makes a large difference. These results are compatible with what is known about extranuclear genomes.
Recombination between two mouset-haplotypes (tw12tfandtLub-1): segregation of lethal factors relative to centromere and tufted (tf) locus
Authors: Condamine Hubert , Guénet Jean-Louis , Jacob François
Published: September 2009

Recombination between two mouset–haplotypes,tw12tfandtLub-1, was investigated by screening the tailless progeny of the cross ♀tw12tf/tLub-1+ × ♂Ttf/+tffor the segregation of tufted phenotype,tw12andtLub-1lethal factors, and metacentric chromosome (sincetLub-lhaplotype is associated with a Robertsonian fusion involving chromosomes 4 and 17). The results give a 17% estimate of the recombination frequency between centromere andtf, withtLub-llethal factor mapping about two-thirds of the distance from centromere totfand thetw12lethal factor behaving as if closely linked totf. This further extends the findings of Silver & Artzt (1981) and of Artzt, McCormick & Bennett (1982), and shows that twot–haplotypes with quite independent laboratory histories recombine at a normal level, supporting the notion that allt–haplotypes basically share the same structure.
Ribosomal suppressors inPodospora anserina: evidence for two new loci by means of a new screening procedure
Authors: Dequard-Chablat Michelle
Published: September 2009

I describe here a new screening procedure to isolate ribosomal suppressors inPodospora anserina. I have used the sporulation defect displayed by an antisuppressor mutationAS7–2. The revertants able to sporulate are due to either true reversions or external mutations. The mutations which restore most efficiently the sporulation show all the properties of ribosomal suppressors and are localized in two new suppressor locisu11andsu12.
Complementation ofnpfmutations in diploid amoebae ofPhysarum polycephalum: the basis for a general method of complementation analysis at the amoebal stage
Authors: Anderson Roger W. , Youngman Philip J.
Published: September 2009

Haploid amoebae ofPhysarum polycephalummay form plasmodia by crossing, a sexual process that involves cellular and nuclear fusions, or by selfing, an asexual process in which the development of a single amoeba into a plasmodium may involve neither cellular nor nuclear fusion. Mutant strains (npf) in which selfing is suppressed were previously assigned to several functional groups on the basis of their ability to cross with one another in certain combinations. In the present study hybrid, diploid amoebae were isolated from both crossing-compatible and incompatible mixtures ofnpfmutants. The diploid amoebae from mixtures of compatible strains readily formed plasmodia by selfing, but selfing was suppressed in the diploids from incompatible mixtures. Thus the crossing tests betweennpfmutants may be viewed as complementation tests: their results reflect the differing selfing abilities of the hybrid, diploid amoebae that formed in each mixture. Genetical and environmental factors affecting the efficiency of formation of diploid amoebae were studied, and the diploids were shown to be stable during repeated subcultures. Although diploid amoebae carrying complementingnpfmutations readily formed plasmodia by selfing at 26 δC, they could be cultured without plasmodium formation at 30 δC, a temperature that also inhibited selfing of the haploidnpf+strains. Ways are discussed of exploiting this combination of properties in a general procedure for isolating and testing diploids for dominance and complementation of amoebal mutations inP. polycephalum.
Segregation of centricY-autosome translocations inDrosophila melanogaster: I. Segregation determinants in males
Authors: Falk Raphael , Baker Shula , Rahat Ana
Published: September 2009

A special screening procedure for the detection of induced Y-autosome translocations with centric breakpoints was applied. A series of Experimental stocks was constructed, each containing a different half of one of the induced T(Y; 2)'s (T element). The three other elements that were involved in the segregation experiments in each stock were a sex chromosome (X element), an inverted chromosome 2 (A element), and a free arm of chromosome 2 (F element). It is not feasible to determine the relative frequencies of all the 16 possible gamete types by mating an Experimental stock to one tester, nor to different testers that have each at least one class of progeny of the same genotype. Each Experimental stock was mated to four different Tester stocks and the data were calibrated so that a coherent segregation pattern could be obtained.

Segregation patterns in meiosis of males from 15 Experimental stocks, each with a different T element were studied. In most Experimental stocks the T element was of the left autosomal arm, while the F element was of the right autosomal arm. In four Experimental stocks the X element segregated independently of the A, F and T elements. In these Group 1 stocks, both the F and the T elements disjoined regularly from the A element. It was concluded that the T element of these stocks had no sex-chromosome disjunction determinants (‘S-determinants’) to interact with the determinants on the X element. Both the T elements and the F elements carried autosomal disjunction determinants (‘H-determinants’) that secured the segregation of the autosomal elements. The H-determinants of the left autosomal arm were qualitatively different from those of the right arm.

In the remaining 11 Group-2 Experimental stocks the X and T elements disjoined regularly, indicating the presence of S-determinants on the T elements of these stocks. The segregation of the T and the A elements in these stocks varied from nearly complete dependence to complete independence. It was concluded that this gradation reflected differences in the quantity of H-determinants present on the T elements of these Experimental stocks. It was impossible to discriminate between a model of continuous H determinants activity and one of a finite discrete number of determinants. The results do not agree with the claim that there are no autosomal disjunction determinants in the proximal heterochromatin of chromosome 2.

The S-determinants on theBsYy+chromosome were located both adjacent to the centromere and distally on the long arm. The latter were probably translocated to the Y chromosome together with theBsmarker.
Metaphase position and orientation of an interchange quadrivalent of Allium triquetrum: II. Changes in position with changes in percentage alternate orientation
Authors: Rickards Geoffrey K.
Published: September 2009

The position and orientation of an interchange quadrivalent in flattened lateral views of metaphase I were studied in inflorescences of an interchange heterozygote of Allium triquetrum showing high, medium and low alternate orientation frequencies. As the overall frequency of alternate orientation changes in these different inflorescences so the positioning of the alternately oriented quadrivalents changes, in that it becomes more like that of the adjacent quadrivalents. The present data argue for the biological significance of the position/orientation data, and imply the presence of two components of alternately oriented quadrivalents with different positional characteristics.
Effect of phosphate levels on the synthesis of acid phosphatases (EC 3.1.3.2) inNeurospora crassa
Authors: Rodrigues Sergio A. , Rossi Antonio
Published: September 2009

When grown on high-phosphate medium, the wild-type strain 74A ofN. crassasynthesized two acid phosphatases, as shown by DEAE -cellulose chromatography. These purified enzymes showed heterogeneity on PAGE, low specific activities towards PNP-P, molecular weight values of at least 300000, no deviation from Michaelian behaviour, and great stability in 50 mM sodium acetate buffer, at pH 5·4, when kept at 54 °C. These acid phosphatases were synthesized in reduced amounts or not at all when the mould was grown under conditions of phosphate starvation, indicating that the level of phosphate also regulates the synthesis of the high molecular weight enzyme forms. When grown on high phosphate medium, thepho-3mutant strain also synthesized two acid phosphatases, whose purified enzymes showed no pronounced differences when compared to those synthesized by the wild-type strain in terms of electrophoretic analysis, specific activities towards PNP-P, molecular weight values, and Michaelian behaviour. However, one enzyme form had a higherKmvalue and a lower heat stability than the corresponding enzyme of the wild-type strain. Even though thepho-3locus might not be responsible for an alteration in the primary structure of the repressible acid phosphatase, it seems clear that the enzymes synthesized by the mould grown on low-or high-phosphate medium must share some structural features. Thus, the drastic differences observed in the molecular properties of the enzymes synthesized by the mould grown under conditions of phosphate starvation as opposed to phosphate repression might be due to an effect exerted by the level of inorganic phosphate in regulating the translation, post-translational modifications and/or excretion, but not necessarily the gene-directed synthesis of distinct mRNAs.
Tests of hypotheses on recombination frequencies
Authors: Morton N. E. , MacLean C. J. , Lew R.
Published: September 2009

Data fromNeurospora,Drosophila, and the mouse support the mapping parameter conventionally used for man, exclude the Haldane, Kosambi, and Carter—Falconer functions, and suggest a refinement for centromere mapping. Different sexes, chromosome arms, and types of data are surprisingly consistent. Double recombination frequencies are accurately predicted, but triple recombination frequencies are overestimated. The centromere appears to act on interference as an obligatory chiasma. Recombination across the centromere conforms to a simple approximation, based on the interval Markov assumption with a common mapping parameter. These results imply that mapping ofnloci requires estimation of at mostnparameters, and the relation between map distances and all recombination frequencies is explicit.
Genetic experiments on sisomicin production byMicromonospora rosea
Authors: Gadó István , Bokány Antónia , Szvoboda György
Published: September 2009

Chromosomal localization of a gene involved in sisomicin production ofMicromonospora rosean.sp. was suggested by the results of matings between antibiotic producer and non-producer auxotrophic mutants. The frequency of producers among prototrophic recombinants varied with the chromosomal markers used for selection. Thesisallele of the parent which was able to overgrow its partner in mixed culture predominated amongst the recombinants.
Cellular autonomy of hyperactivity in segmentalXchromosomal aneuploids ofDrosophilaand dosage compensation
Authors: Prasad-Sinha Jayashree , Mukherjee A. S.
Published: September 2009

Transcription in 9A–11A aneuploid mosaic female larvae ofDrosophila melanogasterhas been assessed autoradiographically. Eleven larvae were found to exhibit mosaicism out of sixty-six larvae scanned and the percentage ofXOandXXnuclei varied from approximately 9 to 100. Irrespective of the number ofXXnuclei present theXOnuclei (duplicated for 9A–11A) invariably showed hyperactivity for both the segments. TheXXnucleus exhibited a dosage effect for all the three segments of 9A–11A. Results support the transcriptional constancy of the entireXchromosome, as proposed by Maroni and Lucchesi. Cellular autonomy of hyperactivity of the singleXchromosome even at the level of segments of theXis thus evident from the present results.
Cell autonomy of two DNA-repair mutations inDrosophila melanogaster
Authors: Ripoll Pedro , Kennison James A.
Published: September 2009

By means of genetic mosaics we have studied the cell autonomy ofmei-41andmei-9, two loci involved in DNA metabolism. The frequency of spontaneous somatic spots resulting from unrepaired chromosome damage and the sensitivity of mutant cells to killing by X-irradiation - two traits indicative of deficient DNA repair - have been analysed at the cellular level. The results show that: (1) The effect of both mutations on chromosome stability is cell autonomous. (2) After 1000 r of X-irradiation practically all the cells homozygous formei-41disappear while about one-third of the cells homozygous formei-9asurvive the irradiation. The possibility of using these mutants as tools to approach developmental problems is discussed.
Inherited cataracts in inbred mice
Authors: West John D. , Fisher Graham
Published: September 2009

Examination of the eyes with a slit lamp revealed that 101/H mice had a coloured cataract. Crosses to C3H/HeH indicated that this was inherited as a single recessive gene which we have designated lop-2 (lens opacity-2). The related strain 129/Sv-SlJ-CP had a phenotypically identical cataract and presumably also carries the lop-2 gene. CBA/H, CBA/CaH- + /p, CBA/H-kd and CBA/H-T6 mice had a bright white or white/green cataract that typically extended from the nucleus to the anterior cortex of the lens. Crosses to C3H/HeH indicated that this was inherited as a semi-dominant gene. However, other crosses raise the possibility that the CBA cataract is also caused by lop-2. If so, the expressivity (and penetrance of the heterozygote) is affected by genetic background. Neither lop-2 nor the gene responsible for the CBA cataract was linked to contrasted (Slcon) on chromosome 10, so these are distinct from the Lop (lens opacity) gene. Further studies of genetic linkage are needed to clarify whether lop-2 is responsible for both the 101/H and CBA/H cataracts.