bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Ph2 mutants promoting homoeologous pairing on spindle sensitivity to colchicine in common wheat
Authors: Ceoloni Carla , Feldman Moshe
Published: April 2011

Two lines of common wheat cv. Chinese Spring carrying mutant alleles for the Ph2 homoeologous pairing-suppressor gene on chromosome arm 3DS promoting homoeologous pairing in wheat interspecific and intergeneric hybrids have been tested for their mitotic sensitivity to colchicine. Both the ph2a mutation, which corresponds to a fairly long deletion of 3DS, and ph2b, which is either an intragenic change or a very small deletion, as well as the ph2a/ph2b heteroallelic combination and the deficiency for the entire 3DS arm (ditelo 3DL), conditioned a significantly lower sensitivity to colchicine than that determined by the wild-type allele Ph2 (euploid and ditelo 3DS). Observation of both metaphase and anaphse root-tip cell populations, treated with various colchicine concentrations, provided similar results. The degree of spindle disruption in 2 × 10−4 M colchicine, as measured by the percentage of fully affected metaphases (C type), was significantly reduced in ph2 and Ph2− genotypes and, consequently, a larger proportion of cells could proceed toward anaphase and also had a regular segregation pattern at this stage. The differential sensitivity of ph2 genotypes to colchicine is in the opposite direction to that previously found for ph1 genotypes, lacking the homoeologous pairing suppressor on chromosome arm 5BL. The ph2 mutation, while promoting homoeologous pairing as ph1 does, decreases spindle sensitivity to colchicine with respect to the wild-type (ph2) allele rather than increasing it, as ph1 does. The observed alteration of spindle sensitivity to colchicine that mutants for structurally unrelated but functionally related genes (Ph1 and Ph2) condition is interpreted as a highly probable coincidence in their cellular target. It is assumed therefore that these loci affect the equilibrium between tubulin and microtubules. Through this effect they presumably determine chromosome positioning in somatic and premeiotic stages, leading to different pairing patterns at meiosis.

Key words: Triticum aestivum, tubulin, pairing suppressors, somatic association.
The meiotic stage of preovulatory oocytes in mares
Authors: King W. Allan , Bezard Jacqueline , Bousquet Daniel , Palmer Eric , Betteridge Keith J.
Published: April 2011

Confusion exists as to whether the oocytes of the domestic horse are ovulated at the first meiotic metaphase (MI) or the second (MII). In this study eight oocytes were collected from the preovulatory follicles of 16 mares 36 h after human chorionic gonadotropin CG treatment. Six of the eight oocytes were judged to be at MII by the presence of the first polar body and this judgement was confirmed by semithin sectioning in one. Of the two that had no polar body, one was found to be at MII after fixation for chromosomal analysis and the meiotic stage of the other remained undetermined. Since all seven oocytes yielding conclusive evidence were at MII, it was concluded that horse oocytes, like those of most mammals studied, are ovulated after completion of the first meiotic division and formation of the first polar body.

Key words: horse, oocytes, ovulation, meiosis, chromosome.
Inheritance of resistance to stem rust in six wheat lines having adult plant resistance
Authors: Knott D. R. , Padidam M.
Published: April 2011

Inheritance of resistance to race 15B-1 of stem rust (Puccinia graminis Pers. f. sp. tritici Eriks, and Henn.) was studied in six lines of wheat (Triticum aestivum L.) having adult plant resistance. The six lines were crossed to a susceptible line and the progenies were advanced to the F5 generation by the single seed descent method. From 91 to 135 F5-derived F7 lines from each cross were tested with race 15B-1 in field nurseries and selected lines were tested in a multirace nursery. The number of genes controlling resistance was estimated by grouping the F7 lines into those as resistant as the resistant parent and other lines, and testing against the ratios expected with various numbers of genes. In 1982, for all six crosses, the segregations fit best to either three- or four-gene ratios. The mean rust severities for the F7 lines in each cross were concentrated at the susceptible end of the distribution. Apparently the genes for resistance had small effects that were multiplicative rather than additive. Under lighter epiphytotics in 1983 and 1984, additional F7 lines were classified as resistant as the resistant parents. The F7 lines were generally more resistant to the multirace mixture than to race 15B-1. The resistant parents probably carried genes for specific seedling resistance to some of the races but in some cases may have carried additional genes for adult plant resistance.Key words: stem rust, Puccinia graminis tritici, wheat, Triticum aestivum, adult plant resistance.
Genetic analysis of resistance to bacterial blight in rice
Authors: Prasad S. C. , Tomar J. B.
Published: April 2011

The mode of inheritance of resistance to bacterial blight, Xanthomonas campestris pv. Oryzae was studied in 12 rice cultivars: 'BR51-282-8', 'DV85', 'CAS209', 'Java14', 'IR4613-54-5', 'Zenith', 'IR36', 'Neuli', 'BJ1', 'LZN', 'MRC603-303', and 'D204-1'. These resistance cultivars were crossed with a susceptible tester parent 'TN1'. The plants were inoculated at the maximum tillering stage by the clipping technique. From the reactions of F1, F2, and F3 populations, it was found that resistance in 'LZN', 'MRC603-303', and 'D204-1' was conditioned by a single recessive gene. The resistance in 'BR51-282-8', 'DV85', 'CAS209', 'Javal4', 'IR4613-54-5', 'Zenith', 'IR36', 'Neuli', and 'BJ1' was controlled by a single dominant gene. The allelic relationships of resistance genes in the test cultivars with Xa4 was studied. The Xa4 gene was originally identified and designated in 'IR22'. The resistance genes in the test cultivars were nonallelic to Xa4. The trisomie lines of 'IR36' were crossed with 'Jaya', a highly susceptible cultivar to bacterial blight. The segregation pattern of the F2 and backcross generations revealed that the resistance gene of 'IR36' was located on chromosome 12 of the rice genome.Key words: rice, resistance, bacterial blight, allelic relationship, trisomics.
Une ébauche de carte cytologique pour le chromosome VII de Petunia hybrida hort.
Authors: Maizonnier D. , Cornu A. , Farcy E.
Published: April 2011

Gamma-ray treatment and telotrisomic analysis were used for cytological mapping in petunia, which resulted in the genetic marking of both arms of the shorter median chromosome of the genome. An4, which is responsible for anthocyanin synthesis in part of the corolla and in the pollen, is located rather distally on the arm called α; both vs5, a mutation for virescent rosettes, and ph3, producing bluish hues of flower anthocyanins, are located on the other arm. The possibility of determining the order and physical distance of the genes with regard to the centromere is discussed. The sketch of a cytological map for chromosome VII revealed, as previously for chromosome VI, a strong inhibition of crossing-over between two genes located on both arms of the chromosome.Key words: petunia, telotrisomy, gene location, deletion.[Traduit par la revue]
Endoreduplication in leaf protoplasts of haploid Nicotiana plumbaginifolia cultured in vitro
Authors: Chen Chi-Chang , Lee Feng-Ming , Kao Yen-Yu
Published: April 2011

When protoplasts isolated from the leaves of haploid plants of Nicotiana plumbaginifolia Viviani were examined cytologically during in vitro culture, a small fraction was found to contain diplochromosomes at the first mitosis. DNA measurements of freshly isolated protoplasts revealed that 92% contained G1 and 8% contained G2 haploid nuclei. The origin of the diplochromosomes was investigated by a simplified sister chromatid differential staining technique and autoradiography. Our results showed that nuclear division in the G1 protoplasts was normal, with each round of DNA replication being followed by mitosis. In the G2 protoplasts, however, one extra round of DNA replication often took place before the nucleus entered mitosis.Key words: Nicotiana plumbaginifolia, protoplast culture, endoreduplication, sister chromatid differentiation.
Induced tetraploidy and trisomic production of Helianthus annuus L.
Authors: Jan C. C. , Chandler J. M. , Wagner S. A.
Published: April 2011

Seedlings of the Helianthus annuus inbred lines P21 and HA89 were treated with colchicine to study chromosome doubling. Frequency of tetraploids, meiotic chromosome pairing, pollen stainability, and fertility were examined. Five-hour colchicines treatments at 0.15%, pH 5.4, with 2% dimethyl sulfoxide resulted in tetraploid sectors on 42% of P21 and 11% of HA89 plants. Tetraploids had larger disk florets and larger pollen grains. Otherwise, tetraploid plants were morphologically similar to their diploid progenitors. Tetraploidy in P21 was not stable, with plants having 2n = 4x = 65 to 70 chromosomes. Tetraploid plants of HA89 had reduced vigor and did not produce seed. At diakinesis, tetraploid P21 plants had an average of 0.85 univalents, 21.12 open bivalents, 6.66 closed bivalents, 0.21 trivalents, and 2.74 quadrivalents per cell. The number of chiasma per chromosome pair in P21 was reduced from 1.50 for diploid to 1.32 for tetraploid plants. Pollen stainability in tetraploid P21 was less than 50% and the plants produced an average of eight seeds per sibbed head, about 1% of normal seed set. Reciprocal crosses of diploid and tetraploid P21 produced four triploid plants. Backcrossing triploids to P21 produced 137 plants with 2n = 34 to 47 + t. Thirty-one of these plants were trisomies having 2n = 35.Key words: Helianthus annuus, tetraploids, triploids, trisomies.
A hybrid zone between Chorthippus parallelus parallelus and Chorthippus parallelus erythropus (Orthoptera: Acrididae): chromosomal differentiation
Authors: Gosálvez J. , López-Fernández C. , Bella L. J. , Butlin R. K. , Hewitt G. M.
Published: April 2011

Two subspecies of the meadow grasshopper Chorthippus parallelus form narrow hybrid zones in the Pyrenees. We studied the patterns of chromosome divergence to evaluate their possible role in the maintenance of such hybrid zones under natural conditions. The two subspecies share some common features such as identical chromosome number, similar basic chromosome form, and the GC-rich nature of all the heterochromatic DNA. Similar positions for the nucleolar organizer region (NOR) in two pairs of autosomes were also observed. The main difference was the presence of an active NOR in the X chromosome in Cp. parallelus that was absent from Cp. erythropus. The pattern of banding by C-banding, acridine orange, and chromomycin A3 also showed the subspecific characteristics on this chromosome. The presence or absence of an active NOR on the X chromosome was used to analyse the hybrid zones in two different transects of the Pyrenees, and clear clines of X NOR frequencies were observed passing from Cp. parallelus to Cp. erythropus. Some meiotic abnormalities were found in individuals from the hybrid zones with the subsequent production of abnormal sperm. Differences in genetic activity involving the sexual chromosome and the male sterility found in F1 hybrids produced in laboratory crosses are discussed as an example of Haldane's Rule.Key words: insect cytogenetics, hybrid zones, speciation.
B chromosomes of the grasshopper Heteracris littoralis: meiotic behaviour and endophenotypic effects in both sexes
Authors: Cano M. I. , Santos J. L.
Published: April 2011

A main type of a large supernumerary B chromosome has been found in several natural populations of the grasshopper Heteracris littoralis. A study on the geographical distribution of the polymorphism and the meiotic behavior of Bs in both sexes has been carried out with special reference to their effect on two endophenotypic parameters: recombination level and macrospermatid production. Male B bivalents are characterized by a high level of pairing and a strict proximal localization of chiasmata. In the females the B chromosome always divides reductionally at anaphase I indicating the possible existence of an accumulation mechanism based on meiotic drive. There is no effect of Bs on either mean chiasma frequency or between-cell variance in either of the sexes. However, in males a positive correlation between the number of Bs and production of abnormal spermatids (macrospermatids) was found.Key words: B chromosomes, chiasma frequency, female meiosis.
Comparison of F2 and F∞ diallel analyses in barley
Authors: Choo T. M. , Reinbergs E. , Jui P. Y.
Published: April 2011

A study was conducted in barley (Hordeum vulgare L.) to compare the relative magnitudes of heterosis to additive × additive epistasis and to compare F2 and F∞, diallel analyses. Both F2 and F∞, progenies were derived from 7 × 7 diallel crosses. Progenies and their parents were evaluated for grain yield, heading date, plant height, and the number of spikes per hill in hill plots with five replications at Elora (Ontario) in 1978. Results suggested that additive × additive epistasis were present for these traits and its magnitude was similar to that of heterosis estimated in F2. Both F2 and F∞ analyses detected the presence of epistasis. Both analyses provided similar estimates of the additive genetic variance for heading date and the number of spikes per hill, but the F2 analysis provided higher estimates than the F∞ analysis for grain yield and plant height. The estimate for grain yield and plant height obtained from the F2 analysis could be biased upward because of the invalid assumption of no epistasis. Estimates of other genetic variance components from the F2 analysis could be biased also. The F∞ diallel analysis not only provided estimates of additive × additive genetic variance for the four traits, it also allowed detection of nonindependent gene distribution in the parents for three of the four traits. Therefore, the limitations of the F2 diallel analysis in the presence of epistasis were apparent in the study. The F2 diallel analysis, however, could be used to detect dominance and maternal effects and thus to complement the F∞ diallel analysisKey words: barley, Hordeum vulgare, diallels, haploids, epistasis, heterosis.
Linkage relationships of 19 allozyme encoding loci within the commercial mushroom genus Pleurotus
Authors: May Bernie , Henley Kathrine J. , Fisher Christine G. , Royse Daniel J.
Published: April 2011

Single spore derived Pleurotus spp. isolates from four commercial lines (two P. sapidus, one P. florida, and one P. ostreatus) and from two interspecific hybrids (P. sajor-caju × P. sapidus) were analyzed for single locus and joint segregation of 25 allozyme encoding loci. The two alleles at the individual loci departed significantly in their segregation from a 1:1 Mendelian ratio in 26% of the intraspecific and 29% of the interspecific tests. Six linkage groups were identified as follows: Dia-1 ~ Est-5; Tpi ~ Pgd-2 ~ Skdh; (Fum) ~ Pgm-2 ~ Pgd-1 ~ PepLgg-1 ~ Gr-2; Ndh ~ Gr-1; Np ~ PepGl-1 ~ Aat-2 ~ Pgk ~ Mup; and Gr-4 ~ Mdh-1. The duplicate loci coding for GR, PEP-LGG, PGM, and PGD were both not linked to each other and not part of duplicate linkage groups. Six loci were not shown to be linked to any other loci (Lap, Pgm-1, Ha, Gpi, PepPap, and PepLgg-2), although the latter two loci were only tested against four and five loci, respectively. The first linkage map of 19 allozyme encoding loci for the Pleurotus genome is presented.Key words: Pleurotus, allozymes, linkage map, inheritance, edible fungi.
Gametophytic competition in pearl millet, Pennisetum typhoides (Stapf et Hubb.)
Authors: Sarr A. , Sandmeier M. , Pernes J.
Published: April 2011

Factors affecting reproductive strategies of pearl millet, which is currently classified as a predominantly allogamous species, were investigated. Gametophytic competition as well as the effect of growth temperature on this phenomenon were studied by means of the pollen mixture technique. The relative competitive ability of pollen from five different genetic stocks (Ligui, Massue, "Chinese," Thiotandé, 23d2B) was assessed by isozyme electrophoresis (esterase, alcohol dehydrogenase) of progeny plants. Gametophytic competition with a polygenic inheritance trend for pollen competitive ability is reported. A better competitive ability of autopollen on various types of allopollen was systematically found for the Ligui genotype. Temperature stress enhanced this trend. Hypotheses on the role of gametophytic competition in the evolution of the primary genetic pool of P. typhoides are discussed.Key words: pearl millet, pollen, competitive ability, segregation distortions.
In vivo and in vitro instability of B chromosomes in palmarosa grass (Cymbopogon martinii var. motia)
Authors: Sreenath H. L. , Jagadishchandra K. S.
Published: April 2011

Meiotic and mitotic instability and elimination of B chromosomes was observed in diploid palmarosa (Cymbopogon martinii var. motia) with 2n = 20 + 1–2 B under in vivo and in vitro conditions. Under in vivo conditions B chromosomes were totally absent from the roots but preferentially transmitted in the germ line tissues. When present as a pair, the B chromosomes formed bivalents showing almost regular orientation, congression, and disjunction. When present singly, the B chromosome formed a univalent and did not pair with any of the A chromosomes and showed nonalignment on the metaphase plate during metaphase I. Immature inflorescences of a race of palmarosa with 2n = 20 + 2 B were cultured on Murashige and Skoog's medium containing 1 mg/L of 2,4-dichlorophenoxyacetic acid to produce embryogenic callus. The cytological analysis of the callus revealed only 20 A chromosomes in nearly all the cells, both the B chromosomes being eliminated. From this callus, plantlets without B chromosomes were regenerated on MS medium without growth regulators and established in the soil. The regenerated plants exhibited 20 A chromosomes with normal meiosis.Key words: Cymbopogon martinii, chromosome instability, palmarosa grass, B chromosomes, tissue culture, plant regeneration.
The yeast ILV2 gene is under general amino acid control
Authors: Xiao W. , Rank G. H.
Published: April 2011

The yeast ILV2 gene encodes acetolactate synthase, the first enzyme in the biosynthesis of isoleucine and valine. Its multiple regulation has precluded the clear demonstration of whether ILV2 is under general amino acid control. Nonderepressible gcn4 strains were used as recipients for transformation with a YCp plasmid carrying GCN4. Parental gcn4 cells and their isogenic GCN4 transformants were evaluated for ALS derepression following induced amino acid starvation. GCN4 cells showed 1.5-to 1.7-fold derepression but no derepression was observed in isogenic control gcn4 strains. A similar depression of ILV2 mRNA was also observed. Genetic evidence for general amino acid control was the gcn4 suppression of high level resistance to sulfometuron methyl by the SMR1-410 allele of ILV2.Key words: Saccharomyces cerevisiae, ILV2 gene, general amino acid control, multiple regulators.
Selection of new biological activities from random nucleotide sequences: evolutionary and practical considerations
Authors: Horwitz Marshall S. Z. , Dube Dipak K. , Loeb Lawrence A.
Published: April 2011

Recent advances in the selection of biologically active DNA sequences from random populations are reviewed. Within the framework of evolution, forces are considered that have precluded the testing of all possible DNA sequences, purely with regard to their functionality as genetic regulatory elements or protein coding sequences. Examples are drawn from cassette mutagenesis of enzyme active sites, protein domain replacement by fusion with random genomic digests, and the selection of bacterial promoters from random DNA. Efforts to derive new activities are examined, and the likelihood of future success is evaluated.Key words: active DNA, nucleotide permutation, DNA evolution.
The molecular–cytogenetic analysis of grasses and its application to studying relationships among species of the Triticeae
Authors: Appels R. , Reddy P. , McIntyre C. L. , Moran L. B. , Frankel O. H. , Clarke B. C.
Published: April 2011

An analysis of four species from the genus Secale, including the study of different accessions, has shown that the properties of DNA clones of monomer units from three repeated sequence loci, namely, Ter, Nor, and 5S DNA, proved to be representative of the entire loci from which they were isolated. This finding in Secale species, including the discovery of a new locus for 5S DNA on chromosome 5R, has been used to interpret information on the Ter, Nor, and 5S DNA loci from 15 species in the Triticeae complex. The evolutionary relationship among species suggested by the DNA sequence data has shown many consistencies with a number of other characters such as those used in classical systematics, as well as geographical distribution data and isozyme and chromosome-pairing studies. Apparent inconsistencies such as a close relationship between the R and P genomes at the Ter loci are interpreted in terms of amplification–deletion phenomena known to occur at repetitive sequence loci. In addition, this study included species endemic to Australia and thus provided a broad time span in which to consider some features of repeated sequence family evolution, such as the conservation of certain parts of 5S DNA spacer regions.Key words: Secale, Triticeae, molecular–cytogenetic analysis.
The physiology of weak selection
Authors: Hartl Daniel L.
Published: April 2011

Reaction rates in metabolic pathways typically exhibit a kind of diminishing returns in which small variations in the activities of the individual enzymes have very little effect on overall flux. These effects are measured by the control coefficients of the enzymes, and most systems are governed by the summation theorem stating that all control coefficients must sum to unity. One implication is that complex systems will not usually contain single rate limiting steps, but rather be controlled to a greater or lesser extent by many enzymes, each exerting relatively small control. Wright understood this principle in 1934 and used it for his physiological theory of dominance. With respect to small variations in enzyme activity, the principle implies that many small variations should have only mild effects on fitness. Analysis of nucleotide polymorphisms in the genes for glucose-6-phosphate dehydrogenase and alkaline phosphatase in Escherichia coli implies that most amino acid replacements are harmful, and that the average selection coefficient against amino acid replacements that are polymorphic in natural populations is 1 × 10−7 to 5 × 10−7. In experiments to determine the a priori distribution of selection coefficients among random amino acid replacements, 25 replacements in β-galactosidase were created by genetic means, and 22 of these produced selective effects too small to be detected in chemostat competition experiments (s < 0.004 per generation).Key words: selection coefficient, control coefficient, nucleotide polymorphism, amino acid replacements.
A grand experiment in evolution: the Drosophila subobscura colonization of the Americas
Authors: Ayala Francisco J. , Serra Luis , Prevosti Antonio
Published: April 2011

Drosophila subobscura is a Palearctic species that has been extensively studied by population and evolutionary geneticists for nearly half a century. In 1978, it appeared in Puerto Montt, Chile; within a few years it extended over much of Chile and into Argentina and became the most common drosophilid in many places. In 1982, it appeared in the American northwest; shortly thereafter it was found extensively distributed from southern British Columbia, through Washington and Oregon, into southern California, west of Sierra Nevada. In North America also it has become a common drosophilid in many places. The source of the colonizers has been sought with four lines of research: sequence arrangement of the polytene chromosomes, allozyme polymorphisms, mitochondrial DNA restriction patterns, and frequency of lethal alleles. The origin of the colonizers remains uncertain, although all evidence indicates that both the North American and the South American colonizers derive from the same Palearctic population. The overall configuration of the chromosomal and allozyme frequencies suggests a western Mediterranean origin, which is consistent with the mtDNA data. The presence of a particular chromosome arrangement, O5, suggests a northern European origin. Lethal allelism has opened up the possibility of discovering the precise origin of the colonizers: all O5 chromosomes in the Americas carry a particular recessive lethal gene. There is strong evidence that the number of founders was not very small and not very large, perhaps between 10 individuals and several score. The chromosomal polymorphisms of D. subobscura exhibit well-defined latitudinal clines in the Old World. In the few years since the colonization, clines in every chromosome have evolved in the Americas that have identical latitudinal polarity with those in the Old World. This would seem strong evidence that the polymorphisms and the clines are adaptive.Key words: chromosomal polymorphism, mitochondrial DNA evolution, allozyme polymorphism, lethal allelism, adaptation, geographic clines.
Natural selection and ribosomal DNA in Drosophila
Authors: Templeton Alan R. , Hollocher Hope , Lawler Susan , Johnston J. Spencer
Published: April 2011

Natural populations of Drosophila mercatorum are variable for the number of X-linked 28S ribosomal genes bearing a 5-kilobase insert. A separate polymorphic X-linked gene controls whether 28S repeats bearing the insert are preferentially underreplicated during the formation of polytene tissue. Female flies having at least a third of their 28S genes bearing the insert and lacking the ability to preferentially underreplicate inserted repeats display the abnormal abdomen syndrome. The syndrome is characterized by retention of juvenile abdominal cuticle into the adult, a slowdown in larval developmental time, and an increase in early female fecundity. The life history traits are expressed in nature and provide a basis for strong natural selection. The abnormal abdomen syndrome should be favored whenever the adult age structure is skewed towards young individuals, and field studies confirm this prediction. The closely related species, Drosophila hydei, also bears these inserts and appears to be subject to similar selection. However, D. mercatorum responds to this selection primarily through the allelic variation that controls preferential underreplication, whereas D. hydei responds primarily through adjustment of the proportion of inserted 28S genes. This is interpreted to mean that the evolution of a multigene family arises from the interaction of population-level and DNA-level processes.Key words: ribosomal DNA, natural selection, concerted evolution, life history, multigene families, Drosophila mercatorum, Drosophila hydei.
Molecular genetic basis of Rhizobium–legume interactions
Authors: Kondorosi A. , Kondorosi E. , Györgypal Z. , Banfalvi Z. , Gyuris J. , Putnoky P. , Grosskopf E. , John M. , Schmidt J. , Ha D. T. Cam , Lados M. , Horvath B. , Slaska-Kiss K. , Schell J.
Published: April 2011

Recognition of the appropriate legume and nodule induction are controlled by common (nod) and host-specific nodulation (hsn) genes in Rhizobium. The nod and hsn genes are activated by the product of the regulatory nodD in conjunction with specific flavonoids excreted by the plant. Differences in the flavonoid specificity of the NodD proteins occur between different Rhizobium species, or between strains of a given species or even within one strain containing several copies of the nodD gene. Accordingly, the nodD gene controls the host-specific expression of nod and hsn genes. In addition, the nodulation genes are under not only positive but also negative regulation which is mediated by a nod-specific repressor protein. This dual control is required for optimal nodulation of the plant host. Further steps in nodule development are again controlled by the infecting Rhizobium. It was found that at least four different classes of Rhizobium fix genes are involved directly or indirectly in the expression of late nodulin genes, finally leading to the establishment of nitrogen-fixing symbiosis.Key words: Rhizobium meliloti, nodulation genes, plant signals, fix genes, alfalfa.
Compartmental and intracompartmental regulation of aging
Authors: Cinader B.
Published: April 2011

Individual differences of aging occur in systems of regulation and communication. Different types of suppressor capacity can change in opposite directions as an individual ages. The progression of these changes in suppressor capacity can be changed to different extents by hormones or diets differing in fatty acid composition. It seems reasonable to conclude that these two activities depend on different precursors which age under the control of two different genes, although the two precursors are almost certainly derived from a common stem cell line. A variety of molecules and activities undergo age-related reductions, which are completed by middle age; the resulting levels of a given gene product are remarkably similar in different individuals, while the levels at a young age show very great individual differences. This correlation between the youthful quantity of a given gene product and the rate of change in later life has been designated as "economic correction." The study of multicentricity of different controlling and of functional competencies of different alleles is an important component in the development of preventive geriatric medicine.Key words: Aging: diets, economic correction – feedback inhibition, hormones: effect on aging progression, multigenic and multiallelic controls of aging, preventive medicine in geriatrics.
Proteins of the inner and outer centromere of mitotic chromosomes
Authors: Earnshaw William C. , Cooke Carol A.
Published: April 2011

We have used immunocytochemistry and molecular cloning methods to identify and characterize structural polypeptides of the centromere. These studies permit us to resolve two distinct regions: the inner and outer centromere, (i) Components of the outer centromere: autoantibodies from certain patients with rheumatic disease identify a family of three immunologically related polypeptides that we have designated CENP-A (17 kDa), CENP-B (80 kDa), and CENP-C (140 kDa). CENP-B has been cloned and sequenced. DNA sequence analysis indicates that this polypeptide possesses two large regions with extraordinary concentrations of acidic residues (region I: 61 residues with 79% glu + asp; region II: 31 residues with 87% glu + asp). Despite this concentration of negative charge, immunocytochemical experiments suggest that CENP-B may be a DNA binding protein. In these experiments, the levels of CENP-B are seen to vary reproducibly from chromosome to chromosome. The role of CENP-B in vivo is unknown. However, it is unlikely to bind directly to the spindle microtubules since it is found at an inactive centromere that apparently does not attach to the spindle. (ii) Components of the inner centromere: we have injected mice with the whole chromosome scaffold fraction to elicit production of monoclonal antibodies. One such antibody identifies two structurally related polypeptides (the INCENP antigens, 135 and 155 kDa) that are preferentially located between the sister chromatids at the centromere. The INCENP antigens undergo dramatic movements from the chromosomes to the central spindle during mitosis. They are ultimately sequestered in the midbody and discarded. Several lines of evidence suggest that the INCENP polypeptides may be involved in the regulation of sister chromatid separation at the metaphase–anaphase transition.Key words: mitosis, centromere, CENP antigens, INCENP antigens, kinetochore, disjunction.
Recognition and elongation of telomeres by telomerase
Authors: Blackburn Elizabeth H. , Greider Carol W. , Henderson Eric , Lee Margaret S. , Shampay Janis , Shippen-Lentz Dorothy
Published: April 2011

Telomeres stabilize chromosomal ends and allow their complete replication in vivo. In diverse eukaryotes, the essential telomeric DNA sequence consists of variable numbers of tandem repeats of simple, G + C rich sequences, with a strong strand bias of G residues on the strand oriented 5′ to 3′ toward the chromosomal terminus. This strand forms a protruding 3′ overhang at the chromosomal terminus in three different eukaryotes analyzed. Analysis of yeast and protozoan telomeres showed that telomeres are dynamic structures in vivo, being acted on by shortening and lengthening activities. We previously identified and partially purified an enzymatic activity, telomere terminal transferase, or telomerase, from the ciliate Tetrahymena. Telomerase is a ribonucleoprotein enzyme with essential RNA and protein components. This activity adds repeats of the Tetrahymena telomeric sequence, TTGGGG, onto the 3′ end of a single-stranded DNA primer consisting of a few repeats of the G-rich strand of known telomeric, and telomere-like, sequences. The shortest oligonucleotide active as a primer was the decamer G4T2G4. Structural analysis of synthetic DNA oligonucleotides that are active as primers showed that they all formed discrete intramolecular foldback structures at temperatures below 40 °C. Addition of TTGGGG repeats occurs one nucleotide at a time by de novo synthesis, which is not templated by the DNA primer. Up to 8000 nucleotides of G4T2 repeats were added to the primer in vitro. We discuss the implications of this finding for regulation of telomerase in vivo and a model for telomere elongation by telomerase.Key words: chromosome telomeres, telomerase, oligonucleotide repeats.
Preferential repair of damage in actively transcribed DNA sequences in vivo
Authors: Hanawalt Philip C.
Published: April 2011

My colleagues and I have discovered intragenomic heterogeneity in DNA repair in mammalian cells. Consequences of unrepaired DNA damage depend upon the precise location of the damage with respect to relevant genes. It is therefore important to understand rules governing accessibility of specific DNA sequences in chromatin to damage and repair. The efficiency of removal of pyrimidine dimers has been determined in the active dihydrofolate reductase (DHFR) gene in Chinese hamster ovary (CHO) cells. Repair within the gene was shown to be much more efficient than that in nontranscribed downstream sequences or in the genome overall. Preferential repair of active and essential genes such as DHFR may account for the fact that rodent cells are as uv-resistant as human cells in spite of their much lower overall repair efficiencies. In repair-proficient human cells the rate of repair in the DHFR gene is greater than that in the overall genome or in nontranscribed α-DNA sequences. The efficiency of removal of pyrimidine dimers is much higher in the transcribed than the nontranscribed DNA strands of the DHFR gene in both CHO and human cells. An excision–repair complex may be directly coupled to the transcription machinery to ensure early removal of transcription-blocking lesions in active genes. Sequences in the active c-abl proto-oncogene are repaired much more efficiently than are sequences containing the inactive c-mos proto-oncogene in Swiss mouse 3T3 cells. Tissue-specific and cell-specific differences in the coordinate regulation of proto-oncogene expression and DNA repair may account for corresponding differences in the carcinogenic response. Efficient replicative bypass of persisting psoralen monoadducts, but not interstrand cross-links, was demonstrated in the human DHFR gene. It is likely that most bulky lesions in mammalian DNA, other than cross-links, do not pose insurmountable problems for replication in vivo, but they must be removed from essential transcribed sequences to maintain cellular viability.Key words: DNA repair, chromatin, transcription, mammalian cells, pyrimidine dimers, ultraviolet light, DNA cross-links.
DNA methylation in plants and its role in tissue culture
Authors: Brown P. T. H.
Published: April 2011

Regeneration of plants via tissue culture often results in a number of plants subsequently showing phenotypic or genotypic deviations from the parental type. This variation has been called somaclonal variation. In an analysis of regenerated Zea mays plants of the inbred line A188, high levels of phenotypic variation were observed. Subsequent analysis of these regenerated plants shows that a high proportion of the regenerants demonstrate significant alterations in the methylation status of both housekeeping and structural genes. These results are described and the theory of gene methylation is reviewed with regard to the differences that exist between plant and animal systems.Key words: 5-methylcytosine, 5-azacytidine, tissue culture, cereals, somaclonal variation.
Risk estimation based on germ-cell mutations in animals
Authors: Favor Jack
Published: April 2011

The set of mouse germ cell mutation rate results following spermatogonial exposure to high dose rate irradiation have been presented as the most relevant experimental results upon which to extrapolate the expected genetic risk of offspring of the survivors of the Hiroshima and Nagasaki atomic bombings. Results include mutation rates to recessive specific-locus, dominant cataract, protein-charge, and enzyme-activity alleles. The mutability as determined by the various genetic end points differed: the mutation rates to recessive specific-locus alleles and enzyme-activity alleles were similar and greater than the mutation rates to dominant cataract and protein-charge alleles. It is argued that the type of mutation event scored by a particular test will determine the mutability of the genetic end point screened. When the loss of functional gene product can be scored in a particular mutation test, as in the recessive specific-locus and enzyme-activity tests, a wide spectrum of DNA alterations may result in a loss and a higher mutation rate is observed. When an altered gene product is scored, as in the dominant cataract and protein-charge tests, a narrower spectrum of DNA alterations is screened and a lower mutation rate is observed. The radiation doubling dose, defined as the dose that induces as many mutations as occur spontaneously per generation, was shown to be four times higher in the dominant cataract test than the specific-locus test. These results indicate that to extrapolate to genetic risks in humans using the doubling-dose method, the extrapolation must be based on experimental mutation rate results for the same genetic end point. Alternatively, the extrapolation could employ the direct-approach procedures. Finally, a direct comparison of the irradiation-induced mutation rate to enzyme-activity alleles in mouse and man indicates no species differences.Key words: ethylnitrosourea, irradiation, mammalian mutagenesis, mouse, dominant cataract mutations, specific-locus mutations, protein-charge mutations, enzyme-activity mutations, doubling dose, human genetic risk.
Evolutionary principles and the regulation of engineered bacteria
Authors: Davis Bernard D.
Published: April 2011

The introduction of engineered bacteria to the environment is being overregulated, on the basis of several assumptions: (i) the danger from deliberate introduction on a large scale is much greater than that from accidental release; (ii) the more distant the source of the DNA the greater the risk; (iii) novel organisms are likely to cause unexpected ecological damage, like that seen with native organisms transplanted to a novel location; (iv) even if the probability of harm is very small, great care must be taken because the harm might be large; (v) products of recombinant DNA must be treated differently from products of classical gentic manipulation; and (vi) our unlimited power to manipulate DNA implies an unlimited power to refashion organisms. Evolutionary principles contradict all these assumptions. Moreover, our increased power of genetic manipulation must be recognized as an expansion of the biotechnology of domestication; and unlike the physical technologies, the long history of domestication has not adventitiously created harmful by-products. I propose that in dealing with such novel and unpredictable developments it would be better to respond with speed and resilience to problems as they arise, rather than to hamper advances by clumsy regulations based on unsubstantiated guesses.Key words: bioengineering, antiscience, biotechnology, risk assessment.
From Daedalus to Mengele: the dark side of human genetics
Authors: Müller-Hill Benno
Published: April 2011

Until recently, the role of scientists in society has been considered sacrosanct. Wherever scientists had been involved in crimes, either the crimes or the quality of science was denied (that is, the science was considered merely pseudoscience). As a result it has been claimed that science can only flourish in democracies but is doomed in other states. So far experience contradicts this opinion. In this paper I discuss the origins of the view that scientists and geneticists in particular, are sacrosanct. I trace it back to the earliest mythological scientists, such as Daedalus and Dr. Faustus. I view the well-known Dr. Mengele as a successor in this tradition.Key words: philosophy, mythology, history.
The politics of human heredity in the USSR, 1920–1940
Authors: Adams Mark B.
Published: April 2011

After the Bolshevik revolution of 1917, Iurii Filipchenko (in Petrograd) and Nikolai Koltsov (in Moscow) created centers of genetic research where eugenics prospered as a socially relevant part of the new "experimental" biology. The Russian Eugenics Society, established in 1920, was dominated by research-oriented professionals. However, Bolshevik activists in the movement tried to translate eugenics into social policies (among them, sterilization) and in 1929, Marxist geneticist Alexander Serebrovsky was stimulated by the forthcoming Five-Year Plan to urge a massive eugenic program of human artificial insemination. With the advent of Stalinism, such attempts to "biologize" social phenomena became ideologically untenable and the society was abolished in 1930. Three years later, however, a number of eugenicists reassembled in the world's first institute of medical genetics, created by Bolshevik physician Solomon Levit after his return from a postdoctoral year in Texas with H. J. Muller. Muller himself moved to the Soviet Union in 1933, where he agitated for eugenics and wrote Stalin in 1936 to urge an artificial insemination program. Shortly thereafter, Muller left Russia, several of his colleagues were shot, and the Institute of Medical Genetics was disbanded. During the next three decades, Lysenkoists regularly invoked the Soviet eugenic legacy to claim that genetics itself was fascist.Key words: Russia, eugenics, human genetics, medical genetics, Lysenkoism, history, politics.
Mobile genetic elements in Drosophila melanogaster (recent experiments)
Authors: Georgiev Georgii P. , Tchurikov Nickolai A. , Ilyin Yurii V. , Georgieva Sofia G. , Mizrokhi Lev J. , Priimägi Andreas F. , Gerasimova Tatiana I. , Georgiev Pavel G. , Simonova Olga B. , Kiselev Sergei L. , Kochieva Elena Z.
Published: April 2011

Recent data obtained in the authors' laboratories concerning the behaviour of mobile genetic elements of Drosophila melanogaster are reviewed. It was found that the mobile element jockey represents the typical LINE element. It is efficiently transcribed in D. melanogaster cells in flies and in culture. Transcription is initiated from the +1 nucleotide of jockey and depends on an internal promoter. This is the first case of an internal promoter being used by RNA polymerase II. Several events which take place during the transposition bursts in ctMR2 family of strains were described. Among them are the removal of mobile dispersed genetics (mdg) elements (with solo long terminal repeat (LTR) remaining at the site of excision), complete removal of an mdg element, and reinsertion of the same mdg to the same place either in the presence or in absence of solo LTR sequence. Finally, the formation of deletions was observed. A 462-bp deletion destroying the white locus can be further repaired (w+ reversion). Thus, transposition bursts include many different genetic events. A novel system of prolonged genome destabilization was described. It depends on mobilization of a new mobile element called Stalker. After certain crosses Stalker actively moves for dozens of generations giving rise to large numbers of insertion mutations. Several novel genes were detected using mobilized Stalker. They include a modifier of mdg4 and six enhancers of yellow mutations.Key words: Drosophila melanogaster, mobile elements, transcription.
Cytogenetic analyses of intersectional hybrids between Parthenium argentatum and Parthenium confertum
Authors: Hashemi A. , Estilai A. , Waines J. G.
Published: April 2011

Induced tetraploid guayule (Parthenium argentatum Gray, a rubber-producing and woody species of section Parthenicaeta) was crossed to P. confertum var. lyratum Gray, a herbaceous species of section Argyrocheta. Hybrids were obtained when guayule was used as female. Like their diploid progenitors, induced tetraploids were sexual and self-incompatible. At meiosis, they averaged 0.30 I, 29.63 II, 0.12 III, and 3.02 IV. Parthenium confertum had 69 chromosomes and was apomictic. At meiosis, it averaged 1.00 I, 32.98 II, and 0.51 IV. Hybrids received 36 chromosomes from guayule and 34 chromosomes from P. confertum. At meiosis, they averaged 0.52 I, 33.44 II, 0.20 III, and 0.50 IV. F1 plants behaved like an amphidiploid in which homologous chromosomes of guayule genome paired with each other and homologous chromosomes of P. confertum genome also paired preferentially. Chromosome association in the hybrids indicated that P. confertum parent may be a tetraploid with suppressed multivalent formation. Although hybrids were partially fertile and produced backcross progeny, the transfer of desirable traits (rapid growth and herbaceous growth habit) from P. confertum into guayule will depend on elimination of preferential pairing in the hybrids.Key words: guayule, natural rubber, meiosis, chromosome pairing.
An assessment of genome analysis based on chromosome pairing in hybrids of perennial Triticeae
Authors: Wang Richard R.-C.
Published: April 2011

Genome analysis based on chromosome pairing in diploid hybrids of perennial Triticeae species was examined along with those interpretations based on data of triploid and tetraploid hybrids and (or) species. The mean arm pairing frequency, c, of diploid hybrids with known genome combinations was used as a measure of chromosome homology. The mean trivalent frequency and the averaged sum of trivalents and quadrivalents were used as indices of pairing in triploids and tetraploids, respectively, to assess the validity of the diploid c values. The relative affinity, x value, of the respective triploid hybrids was also used to assess the c value of a diploid combination. Positive correlation coefficients were found between c values of diploid hybrids and trivalent frequencies in triploid hybrids (r = 0.97) as well as between the former and sums of trivalents and quadrivalents in tetraploid hybrids or amphidiploids (r = 0.92). A lower correlation coefficient (r = 0.65) was found for the comparison between diploid and amphidiploid hybrids involving annual Triticeae species. The c values of diploid combinations were negatively correlated (r = −0.79) with the x values of triploid hybrids. These relationships indicate that chromosome relatedness can be measured by the level of pairing in diploid hybrids of perennial Triticeae. It is also suggested that if the diploid hybrid has a c value of about 0.5, a conclusion regarding the genome relationship should be based on additional evidence, such as karyotype data. It is shown that assignment of genome symbols cannot be guided by the presence or absence of preferential pairing in polyploids. Genes regulating chromosome pairing pose problems for genome analysis but should not invalidate either genome analysis as a whole or that of diploid hybrids in particular.Key words: genome, karyotype, meiosis, hybrid, amphidiploid, triploid, diploid, Triticeae.