bluuebunny/crossref_metadata_2025_split huggingface dataset:
Expression and amplification of the genes for ribosomal RNA in bobbed mutants ofDrosophila melanogaster
Authors: Dutton F. Lee , Krider Hallie M. 
Published: September 2009

SummaryWe have employed stocks bearing clonally derivedXchromosomes to investigate several features of the bobbed mutant syndrome, and the amplification of rDNA genes inD. melanogaster. We report that posterior macroscutellar bristle length correlates well with the rDNA content (i.e. dose ofivs–, or uninterrupted genes) in clonedXderivative strains.X/Omales andX/Xfemales with statistically indistinguishable rDNA contents have virtually identical bristle lengths. This indicates that (with respect to this phenotypic character) the rDNAs in these two genotypes are expressed equally, without apparent sexual dimorphism or dosage compensation. However, the severity of bobbed phenotype in terms of bristle morphology, turgite etching, and delayed eclosion is greater in theXbb/XNO−female than in theXbb/Omale genotype for the alleles examined. We estimate the minimum dose of functioning rRNA genes required for viability at 26 δC to be 70 genes per diploid genome. We have examined the capacity of severalXchromosomes which bear bobbed mutant alleles to compensate inX/Omales, and find that disproportionate replication of these rDNAs does not take place. In contrast, at least one of the non-compensating bobbed alleles does appear to undergo rDNA magnification.
New ara-C resistant mutants of the Chinese hamster ovary cells
Authors: Mishra N. C. , Hinnant Kathryn , Cason Emily 
Published: September 2009

SummaryMutants of Chinese hamster ovary (CHO) cell resistant to cytosine arabinoside (ara-C), an inhibitor of DNA synthesis and antitumour drug, have been isolated and characterized both biochemically and genetically. Mutants occurring spontaneously and those induced by treatment with N-methyl-N′-Nitro-N-nitrosoguanidine (MNG), were obtained at a frequency of 0·24 × 10−6 and 3·4 10−6 respectively. The mutants showed a stable ara-C resistant phenotype which was inherited as a dominant trait in genetic crosses. The wild type (CHO K-1) and the mutant (103, 002 and 003) cells showed no differences in the levels of the uptake of ara-C or of its degradation. Results of biochemical studies further excluded the involvement of deaminase, kinase and ribonucleotide reductase as the possible factor(s) in conferring drug resistance to the mutant cells. However, the wild type and mutant DNA polymerases differed in the level of the in vitro incorporation of specific dNMP in the presence of ara-CTP. These data suggested that the wild-type DNA polymerase which becomes error prone in the presence of ara-CTP may cause the drug sensitivity of the wild-type cells and that a change in the mutant enzyme making it resistant (or less prone) to ara-CTP induced errors in dNMP incorporation may control the drug resistance of the mutant cells.
Crossover frequencies within paracentric inversions in maize: the implications for homologue pairing models
Authors: Maguire Marjorie P. 
Published: September 2009

SUMMARYCrossover frequencies within three overlapping heterozygous paracentric inversions of differing length in the long arm of chromosome 1 of maize were estimated from cytological data. These frequencies were found to be close to normal for the regions involved and directly proportional to the respective physical lengths of these inversions. It is suggested that if pairs of centres which are specialized to regulate homologous pairing of the region between them exist in this part of the maize genome, they are most probably numerous and widely distributed.
A new allele of microphthalmia induced in the mouse: microphthalmia - defective iris (midi)
Authors: West John D. , Fisher Graham , Loutit John F. , Marshall Michael J. , Nisbet Norman W. , Perry V. Hugh 
Published: September 2009

SUMMARYA new allele of microphthalmia (mi) in the mouse was discovered among the progeny of a male that had been treated with the potent mutagen ethylnitrosourea. Homozygotes have white coats, mildly defective bone resorption and small eyes (about 60% of the normal size) with very little pigmentation. The iris and retina are abnormal, there is no vitreous body and iris pigmentation is restricted to a rim around the pupil. No haematopoietic defect was detected. Genetic studies showed that the mutation is linked to lurcher (Lc) on chromosome 6 and crosses withMiwh/ + andmi/ + mice indicate that the mutation is allelic with these two alleles of the microphthalmia (mi) locus. We designate the new allele microphthalmia-defective iris (midi). Somemidi/+ heterozygotes (including the original mutant animal showed a bright ‘red-reflex’ when light was shone directly into the eye and this may have been caused by reduced choroidal pigmentation. Otherwisemidi/ + mice appeared normal. Themidi/micompound heterozygotes had white coats, small eyes, and small teeth; bone resorption was more severely defective than inmidi/mihomozygotes. The osteopetrosis was corrected by treatment ofmidi/mimice with parentalmi/ + bone marrow which suggests that the defect is intrinsic tomidi/mimarrow cells. The coats ofmidi/Miwhcompound heterozygotes were white; the irises were more symmetrical and iris pigmentation was less severely reduced than inmidi/midihomozygotes but pupil dilation appeared to be restricted. Partial complementation occurred in themidi/Miwhcompound heterozygotes with respect to eye size, which was usually near normal.
Preferential transmission in wild common shrews (Sorex araneus), Heterozygous for Robertsonian rearrangements
Authors: Searle J. B. 
Published: September 2009

SUMMARYData from foetal and weanling studies suggest that Oxford race metacentrics kq and no, but not pr, are transmitted preferentially from Robertsonian heterozygote common shrews collected from the Oxford area. These results suggest a possible mechanism for the maintenance of the Robertsonian polymorphism in that area.
A restriction and modification model for the initiation and control of recombination inNeurospora
Authors: Catcheside D. E. A. 
Published: September 2009

SummaryIt is hypothesized that the products of Neurosporarec+genes mask recombinators such ascogby modifying DNA and that unmodified recombinators act as recognition sites for an endonuclease with scission properties like those of the type I restriction enzymes found inE. coli. These cut the DNA in both strands at some variable distance from a recognition site. Repair of a two strand gap initiated in this way would require DNA synthesis using the information contained in the homologous DNA duplex, leading to gene conversion. Crossing over could follow from resolution of two Holliday structures formed during gap repair. The hypothesis explains the polarity in the frequency of conversion events across genetic loci, the observation that chromosomes carrying recombinators are more often converted than is the homologue, and how recombinators can initiate conversion at a distance, as suggested by the pattern of conversion events in thehis-3locus in crosses heterozygous for the translocation TM429.
An assessment of the homoeology of six Agropyron intermedium chromosomes added to wheat
Authors: Forster B. P. , Reader S. M. , Forsyth S. A. , Koebner R. M. D. , Miller T. E. , Gale M. D. , Cauderon Y. 
Published: September 2009

SummarySix wheat/Agropyron intermedium addition lines are described on the basis of their phenotype and biochemical markers. An assessment of homoeology of each addition chromosome is made. Chromosome morphology, plant phenotype, isozyme and protein studies are compared with similar data for other wheat/alien addition lines and other members of the Triticeae. These comparisons give consistent results and it is concluded that addition lines L1, L2, L3, L4, L5 and L7 carry Agropyron chromosomes of homoeologous groups 7, 3, 1, 4, 5 and 6 respectively. This agrees with previously published work with one exception: the L5 chromosome belongs to homoeologous group 5 and not group 2 as proposed by Figueiras et al. (1986).
The influence of mutations on chromosome 17 upon the segregation of homologues in female mice heterozygous for Robertsonian translocations
Authors: Ruvinsky A. O. , Agulnik S. I. , Agulnik A. I. , Belyaev D. K. 
Published: September 2009

SummaryThe influence of mutations in chromosome 17 upon the segregation of the metacentric and acrocentric homologues in the progeny of female mice heterozygous for Robertsonian translocations Rb(8.17)11em and Rb(16.17)7Bnr was studied. Genetic analysis indicated that the portion of non-Rb (normal karyotype) progeny from mothers heterozygous for mutations tf, qk, t12 was weakly different from the 50% Mendelian expected level (55–57%). Introduction of mutations T, FuKi, Fu, t6 into the female genotype caused a stronger segregation distortion and an increase in the portion of progeny with normal karyotype (63–67%). From the data on embryonic mortality and cytogenetic observations it is concluded that a distortion of equal transmission arises before M II of meiosis. Consequently, the preferential distribution of the metacentric chromosome to the polar body during the first meiotic division is relevant to the observed segregation distortion.
Heritability of body size in a natural population of the Great Tit (Parus major) and its relation to age and environmental conditions during growth
Authors: Noordwijk A. J. Van , Balen J. H. Van , Scharloo W. 
Published: September 2009

SummaryWe have analysed data on weight and tarsus length collected during a long-term study of natural populations of Great Tits to evaluate the relative importance of genetic variation in body size. Some of our data were collected over a 25-year period, and therefore include a relatively large sample of naturally occurring environmental conditions. An overall heritability estimate calculated from the uncorrected mean weights of breeding birds amounts to 0·5. This estimate is unlikely to be influenced by resemblance in environmental conditions between relatives. Heritability estimates based on the size of fledglings vary between zero and the value for adults, depending on the environmental conditions during growth. If the feeding conditions for the nestlings are poor, no resemblance between parents and offspring is observed. Selection against small nestlings acts strongly on the environmental variance. This is concluded from the higher heritability estimates in the same cohorts after survival for at least three months after fledging, compared to measurements on nestlings. Such selection acting differentially on the genetic and environmental components of the phenotypic variance has important consequences for our ability to make predictions of phenotypic change from measured natural selection. Nevertheless, the amount of genetic variation would allow rapid response should selection on adult size occur.
Cytogenetic analysis of theechinoid (ed), dumpy (dp)andclot (cl)region inDrosophila melanogaster
Authors: Szidonya János , Reuter Gunter 
Published: September 2009

SummaryThe chromosomal region surrounding theed, dpandclgenes has been studied cytogenetically (24–26 on 2L chromosome). It contains threeMinutesand a haplo-sterile function. For isolation of deficiencies and mutations these haplo-insufficient functions were covered by an insertional translocation of 24D4-25F2 into the X chromosome, or by tandem duplications. 112 lethal and visible mutations induced by EMS and X-rays have been localized by deficiency mapping to 20 subregions. They specify 42 loci in a 48 band interval consistent with the notion that most of the bands encode a single lethal function. Thedp, DTS, tkvand suppressor/enhancer loci for position-effect variegation were studied in detail. A dominant suppressor function was localized within the structural part of thedpcomplex. New non-conditional lethals have been isolated for theDTSlocus. Complementation analysis with the previously identified dominant heat-sensitive alleles places the site for heat sensitivity in the middle of the locus. Two haplo-abnormal enhancers of position-effect variegation were localized in the region 25F2–26A1. A triplo-abnormal suppressor function maps to 26B2–5; 26B9. The dose-dependent functions of these loci were studied by the use of deficiencies and duplications.
Contribution of recombinants produced by female flies heterozygous forEst-α alleles to genie variation ofDrosophila virilis
Authors: Tsuno Kendo 
Published: September 2009

SummaryWith 12 alleles at theEst-α locus ofDrosophila virilis, 44 genotypes of females heterozygous for a pair of them were constructed, and about 4 × 104of their F1progenies per genotype were electrophoretically examined. Eighty-three variants different from both of their parental alleles were obtained from a total of 2·0 × 106progenies. Statistical analysis suggested most of their variants to be recombinants. And no null or inactive allele, of which frequency is several percent in natural populations, appeared in 11·6 × 104progenies from females heterozygous for active alleles. These results suggest that the high variation of theEst-α locus in this species is generated by recombinants from female heterozygotes.
Fertility of sperm from t/ + mice: evidence that + − bearing sperm are dysfunctional
Authors: Olds-Clarke Patricia , Peitz Betsy 
Published: September 2009

SummaryMale mice carrying one complete t haplotype transmit it to virtually all offspring. This implies that either the sperm carrying the t haplotype have an advantage in fertilization, or that the sperm not carrying a t haplotype are dysfunctional. To distinguish between these possibilities, epididymal sperm from tw32/ + and congenic + / + males were artificially inseminated into the uterus of T / + females, and the transmission ratio determined from the phenotype of the offspring. After artificial insemination (AI) of sperm from tw32/ + males, the mean ratio was 0·95 (3 experiments, 5 litters), demonstrating that the transmission ratio remains high after AI into the uterus. After AI of a mixture of equal numbers of motile sperm from tw32/ + and congenic + / + males, the mean ratio was 0·22 (6 experiments, 8 litters). These results suggest that sperm carrying a t haplotype from t/ + males are not superior to sperm from + / + males, and therefore imply that sperm not carrying a t haplotype from t/ + males are dysfunctional.
Chromosomal location of peptidase, PEPT-1, genes in Triticum aestivum var. Chinese Spring
Authors: Golenberg Edward M. 
Published: September 2009

SummaryDitelocentric accessions of the Chinese Spring cultivar of Triticum aestivum were analysed electrophoretically for peptidase (PEPT) and amino peptidase (AMP = LAP) activity. Isozymic activity was missing in the accessions CSDT6AS and CSDT6BS when stained for PEPT. This was taken as evidence that the structural genes encoding these isozymes are located on the long arms of chromosomes 6A and 6B. These genes have been named Pept-A1 and Pept-B1, respectively. Isozymic activity was missing in the CSDT6BL accession when stained for AMP. This result reconfirms the previously published location of the gene Amp-B1 on the short arm of chromosome 6B and demonstrates that the two sets of loci are clearly different.
Persistence of a lethal t haplotype in a laboratory stock of outbred mice
Authors: Silver Lee M. , Lukralle Deborah , Garrels James I. , Willison Keith R. 
Published: September 2009

SUMMARYA cryptic, lethal t haplotype (named tLmb) has been discovered in the non-inbred MF1 laboratory stock of mice. Detailed genetic and molecular studies demonstrate a close relationship between tLmb and a well-studied t haplotype, t6, previously extracted also from a laboratory stock. It appears likely that t6 is an aberrant t haplotype derived by recombination from a tLmb-like ancestral chromosome. The persistence of tLmb through 40 years of random breeding in a laboratory stock indicates that high transmission ratio distortion is sufficient to overcome the deleterious effect of a recessive lethal gene in a mouse population.
The tabby locus (Ta) in the mouse: its site of action in tail and body skin
Authors: Pennycuik Pamela R. , Raphael Kathryn A. 
Published: September 2009

SUMMARYBy means of grafting skin in which the epidermis of one genotype was combined with dermis of another to a nude host, we have shown that the effect of the mutant at the tabby (Ta) locus on follicle initiation in tail skin was not confined to either the epidermis or the dermis, that the effect ofTaon the morphology of body hairs was determined by the epidermis but that the close proximity of epidermis of a different genotype also affected body hair morphology.
Protein and amino acid composition of hair from mice carrying the naked (N) gene
Authors: Raphael Kathryn A. , Marshall R. C. , Pennycuik Pamela R. 
Published: September 2009

SummaryThe protein and amino acid compositions of hair from mice carrying the naked (N) gene were compared with those of wild-type (+ / +) mouse hair using two-dimensional polyacrylamide gel electrophoresis and amino acid analysis. In samples obtained from N /+ mice, the numbers of positions of the low-sulphur (LS), high-sulphur (HS) and high tyrosine (HT) protein spots were indistinguishable from those observed in + / + samples but the amount of HT protein was reduced in N / + hair. In samples obtained from N /N mice the protein spots were fewer than, and perhaps different from, those in samples from the other two genotypes; all protein classes were represented but the HS and HT protein content appeared to be less than that in + / + and N / + hair. Amino acid analyses of hair samples showed that the HS contents of + / + and N / + hair were approximately the same, whereas the HT protein content of N / + hair was about half that in + / + hair. N / N hair contained less half-cystine and tyrosine than + / + and N / + hairs, but because the contents of proline, threonine and glycine were unexpectedly high, it appears that protein components of unusual composition are present in N / N hair. It was concluded that the gene at the N locus is involved only indirectly in the synthesis of the structural proteins found in mouse hair.
A model of extranuclear genomes and the substitution rate under within-generation selection
Authors: Takahata Naoyuki 
Published: September 2009

SummaryA single locus model of extranuclear genomes is developed under the assumption of the complete action of within-generation drift which is caused by random transmission of multiple copy genomes during cell division in a generation. Within-generation drift segregates different copy genomes in a cell into different cells, resulting in homoplasmic cells. Under some conditions, the present model reduces to that for haploid nuclear genomes. A point overlooked in previous models is that the multiplicity also admits of the possibility of selection occurring within a cell or between cells in an individual (within-generation selection). If there is selection mediated by, for instance, differential proliferation of genomes, then a haploid model no longer explains the dynamics of extranuclear genomes. Rather a model analogous to biased gene conversion at a single locus (Nagylaki, 1983; Walsh, 1983) is more appropriate. An application of this model to either the fixation probability or substitution rate of new mutations shows that strictly maternal inheritance does not allow the fullest use of mutations, as it obscures the effect of within-generation selection. But if there is appreciable paternal contribution, within-generation selection could be a strong evolutionary force to which nuclear genomes are never exposed.
Genetic analysis of the sexual dimorphism of glass inDrosophila melanogaster
Authors: Birchler James A. 
Published: September 2009

SUMMARYA modifier locus is described that alters the level of phenotypic expression of the third chromosome mutant glass in a sex specific manner. Alternative alleles either confer a sexually dimorphic level of pigment in glass mutants, with the male being greater, or cause similar expression in the two sexes. The alleles are indistinguishable in females but produce the respective phenotypes in males. The gene maps to the tip of theXchromosome at position 0·96 ± 0·11. Cytologically, the locus is present between polytene bands 3A6–8 and 3C2–3 as determined by its inclusion in translocatedXsegments inw+Y,Dp(l;2)w70h31andDp(l;3)w67k27The dimorphic allele is dominant to the nondimorphic condition in males heterozygous for an insertional translocation carrying the dimorphic allele and a normal chromosome carrying the nondimorphic form. The dimorphic allele in two doses in males does not exhibit a dosage effect. The modifier phenotype is unaffected in twoXflies by the presence of the transformer mutation.
Antagonism between novobiocin and coumermycin A1inBacillus subtilis
Authors: Gadó István , Széll Valéria , Büki Kálmán , Szvoboda György 
Published: September 2009

SUMMARYWhen combinations of inhibitors acting on the subunit B of DNA gyrase were tested inBac.subtilisstrains, the growth-inhibiting effect of novobiocin was specifically antagonized by subinhibitory concentrations of coumermycin A1. An antagonism in the opposite direction was not observed.Two alternative models are proposed, where the supercoiling decrease caused by novobiocin is antagonized by coumermycin.This phenomenon seems to be characteristic of theBac.subtilisspecies.
The genetic correlation between characters maintained by selection, linkage and inbreeding
Authors: Lande Russell 
Published: September 2009

SUMMARYMutation is modelled in two quantitative characters under separate genetic control in a large population. A bivariate pattern of selection acts to correlate the characters and, without pleiotropy, their genetic correlation is due entirely to linkage disequilibrium. Data on spontaneous mutation, the effective number of genes, and the intensity of natural selection on quantitative characters are used to evaluate the models. It is concluded that, even when selection favors a high correlation between the characters, with random mating and no linkage between loci influencing different traits the genetic correlation between characters is likely to be small in magnitude. A genetic correlation of large magnitude can be maintained only if the loci influencing different characters are tightly linked, or there is a high level of inbreeding in the population created by frequent mating between closely related individuals.
Suppression of ribosomal RNA genes inDrosophila melanogaster
Authors: Kalumuck K. E. , Procunier J. D. 
Published: September 2009

SUMMARYThe rDNA of fiveYchromosome mutants was examined with respect to their insert free (In−) repeat type multiplicity. The In− repeat number of each mutant was correlated with its hemizygousbobbedphenotype and additivity with anXNObobbed(bb) mutant. Four of these mutants showed a direct relationship between their In− frequency, hemizygousbbphenotype and additivity tests. A fifth mutant,bb1–4, had a sufficient number of In− repeats to ensure viability to the late pupal stage and show additivity; however, the In− repeats genetically behaved as a complete rDNA deletion. Possible mechanisms resulting in the suppression of thebb1–4In− repeats are discussed.