bluuebunny/crossref_metadata_2025 huggingface dataset:
Cytogenetic stability of maize tissue cultures: a cell line pedigree analysis
Authors: Benzion Gary , Phillips Ronald L.
Published: April 2011

Cytogenetic instability in maize plants regenerated from tissue culture is a commonly observed phenomenon. In an attempt to understand the origin of this instability meiotic analyses were performed on 370 regenerated plants that were initiated from cell lines of 22 immature embryos of 9 maize genotypes. Cell lineage pedigrees were maintained on these cultures to record the familial relationship between regenerated plants. Overall, 12.4% of the 370 régénérants contained cytological aberrations. The largest category of aberrations involved chromosome breakage (translocations, deletions, and an inversion) between a heterochromatic knob or knob site and the centromere. Late replicating knob heterochromatin might have been responsible for the chromosome breakage events. Cytologically identical aberrations were observed in plants regenerated at various time points in the pedigreed cultures, indicating an early occurrence of the aberration during culture maintenance. Heterogeneity of cell karyotypes also was observed within embryo cell lines. Multiple independent aberrations occurred within a single embryo cell line. The pedigree of the cultures provided evidence that the sectoring of regenerated plants was due to a multicellular origin of meristematic areas. The frequency of cytogenetically abnormal plants recovered increased with culture age. The data presented are consistent with the age effect not being due to an increased mutation rate but due to mutational events that occurred throughout culture development with a subsequent maintenance and accumulation of aberrant cells over time.Key words: Zea mays, cytogenetic stability, tissue culture, somaclonal variation.
Implications of chromosome pairing in a monohaploid and its colchidiploid of Solanum tuberosum (x = 12)
Authors: Singh A. K. , Uhrig H. , Salamini F.
Published: April 2011

A monohaploid (x = 12) of Solanum tuberosum, its colchidiploid and their 2n parent clone have been cytologically examined. The meiotic analysis of the monoploid shows a certain degree of pairing at pachytene with a high frequency of bivalents at metaphase I. The bivalent frequency ranges from 2.07 to 3.0 per pollen mother cell (PMC). The most frequent classes are 3II + 6I and 2II + 8I. Several PMCs show secondary associations. At anaphase I (AI), the chromosomes distribute frequently in groups of 7 to 5 (32% of PMCs) and 6 to 6 (30% of PMCs). Occasionally, however, both disjunct chromosomes and univalents remain at the equatorial plane and divide with or without segregation, resulting in the formation of dyads or monads. The PMCs with a regular AI show a parallel orientation of spindles as well as a normal one, a situation that ends at telophase II with dyads, triads, and tetrads but 0% pollen fertility. The overall frequency of monads, dyads, triads, and tetrads is equal to 13, 69, 7 and 11%, respectively. Both in the parent clone and in the 2n colchidiploid clone, chromosome pairing is normal. The pairing behaviour in the monohaploid suggests the presence of duplicated sequences in the chromosome complement. An alteration of genes controlling the level of pairing is excluded.Key words: monohaploid, colchidiploid, chromosome pairing, meiosis.
Diploid perennial intergeneric hybrids in the tribe Triticeae. IV. Hybrids among Thinopyrum bessarabicum, Pseudoroegneria spicata, and Secale montanum
Authors: Wang Richard R.-C.
Published: April 2011

Diploid intergeneric hybrids among Thinopyrum bessarabicum, Pseudoroegneria spicata, and Secale montanum were synthesized with the aid of embryo rescue. Karyotype analyses of mitotic root-tip cells revealed that all satellited chromosomes in the J, S, and R genomes were present in their hybrid combinations, making it possible to identify these hybrids at the seedling stage. Spikes of these hybrids were intermediate to, but distinctly different from, those of the parental species. Meiotic chromosome associations at metaphase I in the pollen mother cells averaged 4.34 I + 2.77 rod II + 1.42 ring II + 0.24 III + 0.14 IV for P. spicata × T. bessarabicum; 11.05 I + 1.22 rod II + 0.04 ring II + 0.13 III + 0.01 IV for T. bessarabicum × S. montanum; and 12.98 I + 0.52 rod II + 0.01 III for P. spicata × S. montanum. These meiotic data suggest that the S genome of Pseudoroegneria and the J genome of Thinopyrum are more closely related to each other than they are with the R genome of Secale. The R genome is slightly closer to the J genome than to the S genome. Since these synthetic hybrids represent genomic combinations that may not exist in nature, their induced amphiploids should be created and evaluated.Key words: intergeneric hybrids, genome, phylogeny, Thinopyrum, Pseudoroegneria, Secale.
Analyses multivariées de descendances de rétrocroisements et mise en évidence de distorsions de ségrégation de caractères quantitatifs chez le mil (Pennisetum typhoides (Burm.) Stapf et Hubb.)
Authors: Sarr A. , Pernès J.
Published: April 2011

Evidence for self-pollination predominance and pollen competition was derived from certain genotypes of pearl millet (Pennisetum typhoides). In the present study, the impact of such phenomena was analyzed, using F2 and backcross lineages resulting from crosses between two millet lines, namely Ligui and Massue. Four backcross families were involved: BC1a (Ligui ♂ × F1), BC1b (F1 ♂ × Ligui), BC2a (Massue ♂ × F1), BC2b (F1 ♂ × Massue). Concatenating the multivariate analysis methods allowed the division of each family into subgroups of affinities. This procedure resulted in disclosing a distortion of the global segregation in favor of the Ligui parent. To explain such distortions, a model including gametic and gametophytic selections is proposed. Besides the utilized statistical methodology, which might prove very effective in sorting out backcross lineages early in selection programs, implications of character differential transmission at the level of population genetic structure are discussed.Key words: Pennisetum typhoides, intergametophytic competitions, segregation distortion.
C-banding and nucleolar activity of tetraploid Avena species
Authors: Fominaya A. , Vega C. , Ferrer E.
Published: April 2011

The Giemsa C-banding pattern of the chromosomes of five tetraploid species of Avena have been studied. The chromosomes of AABB species (A. barbata, A. vaviloviana, and A. abyssinica) had similar C-banding patterns to those of A genome species. AACC species (A. maroccana and A. murphyi) possessed two sets of seven chromosome pairs with C-banding patterns similar to those observed in the diploid A and C genome species. However, no good correspondence between either of these two chromosome groups and any one diploid species has been found. When the nucleolar organizer activity of the species was analysed by silver staining, fewer nucleoli and nucleolar organizer regions (NORs) were observed than expected, assuming complete additivity of those from the donor diploid species.Key words: C-banding, NOR, Avena, heterochromatin.
The arrangement of Pisum chromosomes in interphase
Authors: Wolff Gisela , Quednau Hans-Dietrich
Published: April 2011

Root tip cells of Pisum sativum were analyzed for the position of two chromosomes (4 and 7) that carry the nucleolar organizing region. Because of a characteristic heterochromatic pattern of these chromosomes, they can be identified in interphase. The positions of these regions were measured in relation to the center of the nucleus and to one another. The values were statistically evaluated by means of multiple tests of significance. The results discussed show clearly that in P. sativum cells the distribution of the nucleolar organizing chromosomes is not random and that the chromosomes analysed occupy special sites. There was no evidence that homologous chromosomes are more adjacent than heterologous ones, nor that morphologically similar chromosomes are neighbours. The present investigations have also shown that the position of the chromosomes is altered if the structure of the chromosomes is changed by reciprocal translocations.Key words: chromosome position, somatic pairing, translocation, heterochromatin, C-banding, multiple tests of significance.
Mathematical models for estimating preferential pairing and recombination in triploid hybrids
Authors: Sybenga J.
Published: April 2011

Different mathematical models for estimating pairing and recombination parameters for triploid hybrids with two-armed chromosomes are discussed. In most models all information on preferential pairing is contained in the ratio of trivalents and ring bivalents and can be estimated independently of the chiasmate association frequencies in the two chromosome arms. The single degree of freedom available only permits the estimation of ranges of the three possible pairing relations between the three genomes. Alternatively, a single parameter can be estimated when additional assumptions are made. When the ratio r between the frequencies of trivalents and ring bivalents, independent of arm length differences and with a theoretical maximum of 2, is about 1, the ranges of the frequencies of the three pairing combinations are wide. When r becomes smaller than 1, very soon the ranges become limited to values where one of the three is relatively large and positive and the other two negative and varying between equal to very different, depending on slight changes in the first. When the frequency of open bivalents is relatively high and the frequency of univalents low, there most probably is a difference in chiasmate association frequency between the two arms of the average chromosome and this difference can be quantified. When the number of univalents is only slightly higher than expected on the basis of the number of open bivalents, the reason may be that (quantifiably) more chiasmata are formed after bivalent pairing than after trivalent pairing within certain ranges of r, and certain ranges of the average chiasmate association frequency. When the excess of univalents is larger, this is best explained by a failure of entire chromosomes to find each other. This degree of pairing failure can be estimated. All models have been applied to the triploid hybrid between allotetraploid Trifolium repens and diploid T. nigrescens. Assuming that the two genomes of T. repens do not pair, which cannot be demonstrated with certainty, the two genomes pair with the nigrescens genome with frequencies of 0.828 and 0.171, respectively. Introgression then occurs into either genome but not with the same frequency. If the repens genomes pair, this would be caused by either genetic factors disturbing the normal pairing behaviour or the absence of strict homologues. Then the relative pairing frequency between T. nigrescens and one of the T. repens genomes would be 0.838 and on an average 0.081 between the two other combinations, with a possibly considerable but unknown difference. The high average chiasmate arm association frequency (0.650) suggests that affinity between the pairing genomes is not very low. The average two arms do not differ in chiasma frequency.Key words: triploid hybrids, preferential pairing, recombination, mathematical models, Trifolium.
Estimation of phenotypic selection differentials for predicting genetic responses to ratio-based selection
Authors: Mather D. E. , Gunsett F. C. , Allen O. B. , Kannenberg L. W.
Published: April 2011

Ratios of the phenotypic values of two traits may be used as selection criteria in animal and plant breeding to improve the ratio traits themselves or to effect changes in their two component (numerator and denominator) traits. Prediction of genetic responses to ratio-based selection would facilitate quantitative analysis and evaluation of selection based on ratios. Methods for predicting such responses are derived and presented here. They employ expressions for the truncation value of a ratio and for the phenotypic selection differentials of the numerator and denominator traits. The derivation of these expressions is based upon the assumption that the phenotypic values of each of these traits are normally distributed. Worked examples relating to livestock and crop improvement are included to demonstrate how responses to selection for ratios may be predicted.Key words: ratio selection criterion, selection differential, genetic response.
Genetics of Glossina morsitans morsitans (Diptera: Glossinidae). XIII. Mapping the locus for tetrazolium oxidase in linkage group I and refinement of the linkage group II map
Authors: Gooding R. H. , Rolseth B. M. , Tarimo S. A.
Published: April 2011

The locus for tetrazolium oxidase, To, is mapped at 4.3 ± 1.3 recombination units from the locus for arginine phosphokinase, Apk, in linkage group I, and the distance between the eye color locus, sal, and Apk is confirmed to be about 39.5 ± 3.2 recombination units. In linkage group II the loci for aldehyde oxidase, Ao, and for two esterases are arranged in the order Ao Est-1 Est-2 with 3.5 ± 1.2 recombination units separating Ao and Est-1 and 8.3 ± 1.8 recombination units separating Est-1 and Est-2.Key words: Glossina morsitans, tetrazolium oxidase, aldehyde oxidase, esterases, linkage maps.
A reassessment of genome relationships between Thinopyrum bessarabicum and T. elongatum of the Triticeae
Authors: Jauhar Prem P.
Published: April 2011

Chromosome pairing and chiasma frequency in diploid (2n = 2x = 14; JE genomes), amphidiploid (2n = 4x = 28; JJEE), and triploid (2n = 3x = 21; JJE) hybrids between Thinopyrum bessarabicum (2n = 2x = 14; JJ) and T. elongatum (2n = 2x = 14; EE) were analyzed. The diploid hybrids (JE) showed a mean pairing of < 0.01V + 0.30IV + 0.28III + 4.98II + 1.97I with 8.36 chiasmata per cell. The pairing was rather poor, most bivalents being rod-shaped; some were clearly hetero-morphic and loosely paired (probably pseudochiasmate). The diploid hybrids were sterile, showing the reproductive isolation of the parental species. The JJE triploid had a mean chromosome configuration of < 0.01VI + 0.06IV + 1.53III + 5.46II + 5.20I with a chiasma frequency of 13.45 per cell. Chromosomes of the duplicated genome JJ showed preferential pairing, forming mostly ring bivalents with two or even three chiasmata each, as in the T. bessarabicum parent; most chromosomes of the E genome remained as univalents. Thus, the E genome chromosomes offered little synaptic competition to the chromosomes of the duplicated JJ genome. The degree of preferential pairing was even stronger in the JJEE amphidiploids, which predominantly showed bivalent pairing with up to 14 ring bivalents in some cells. They had a mean pairing of 0.01VI + 0.55IV + 0.26III + 11.75II + 1.42I; the mean quadrivalent frequency per cell varied from 0.10 to 1.53. Thus J and E genomes essentially maintained their meiotic integrity at the 4x level. This pattern of chromosome pairing in hybrids at different ploidies and the sterility of diploid hybrids show that J and E are distinct genomes and that there is little justification for merging them, as suggested by previous workers. The J and E are homoeologous at best. The merger of Lophopyrum (E genome) with the genus Thinopyrum (J genome) would be improper. Although the J and E genomes are close enough to permit some intergenomic gene flow, which may be exploited in plant breeding, they are certainly not close enough to have the same genomic designation. The JJEE amphidiploids are meiotically stable and may be a useful source of genes for wheat improvement.Key words: genome, meiosis, chromosome pairing, phylogenetic relationships, Thinopyrum, interspecific hybrid, autoallo-triploid, amphidiploid.
Elimination of multivalents during meiotic prophase in Scilla autumnalis. II. Tetraploid
Authors: Jenkins G. , White J. , Parker J. S.
Published: April 2011

The pairing behaviour of chromosomes during meiotic prophase in two Scilla autumnalis tetraploids was investigated by observing synaptonemal complexes from serial sections and whole-mount surface spreads. In one of the tetraploids with the genomic constitution AAB7B7 pairing at first metaphase of meiosis is restricted to homologous chromosomes and only bivalents appear. In the second tetraploid, AB7B7B7, some multivalents are found at first metaphase, but most of the configurations are bivalent. The bivalents, however, result from chiasma formation between homoeologous as well as homologous chromosomes. Both tetraploids show extensive multivalent formation at zygotene. The transformation of these multivalents to bivalents is described and interpreted in the two tetraploid forms.Key words: Scilla autumnalis, synaptonemal complex, multivalents, elimination, polyploids.
The effect of different doses of Ph1 on chromosome pairing in hybrids between tetraploid Agropyron elongatum and common wheat
Authors: Charpentier A. , Feldman M. , Cauderon Y.
Published: April 2011

Chromosome pairing at first meiotic metaphase was studied in F1 hybrids between tetraploid cytotypes of Agropyron elongatum and common wheat lines of the cultivar Chinese Spring, carrying zero, one, and two doses of Ph1. The bivalentization gene system of A. elongatum could not compensate for the absence of Ph1: hybrids deficient for this gene exhibited pairing between the Agropyron E1 and E2 chromosomes, between the wheat A, B, and D chromosomes, and between the Agropyron and the wheat chromosomes. In hybrids with one or two doses of Ph1, pairing was restricted to the Agropyron E1 and E2 chromosomes. It was concluded that E1 and E2 are distant homologues, thus further supporting the autoploidy nature of tetraploid A. elongatum. The genomic relationships in other polyploid species of the genus Agropyron is discussed in the light of this evidence.Key words: chromosome pairing, Triticum, common wheat, Agropyron.
Scope of action of the immunoglobulin mutator system
Authors: Wabl Matthias R. , Jäck Hans-Martin , Borstel R. C. von , Steinberg Charles M.
Published: April 2011

The authors have developed a method to measure the rate of spontaneous mutations taking place in IgH, the gene encoding the immunoglobulin heavy chain. When an amber chain-termination codon mutates to a sense codon, translation of the polypeptide chain will be completed, and mutant cells producing the heavy chain can be detected with a fluorescent labelled antibody. The protocol used is the compartmentalization test which minimizes any effect of selection. In subclones of the pre-B lymphocyte line 18–81, the spontaneous mutation rate in the part of IgH encoding the variable region is somewhat greater than 10−5 mutations per base pair per generation. This supports the hypothesis that hypermutation is not dependent on cell stimulation by an antigen. In a hybrid between a cell of this line and a myeloma (which represents the terminal stage of the B-cell lineage), the mutation rate was too low to be determined by this test, less than 10−9. When the same loss to gain procedure system was used with an opal chain-terminating codon in the part of IgH encoding the constant region (Cμ), a high rate of reversion by deletion was found. Long (more than one exon) and short (less than one exon) deletions occurred at rates of 1.7 × 10−5 and 1.4 × 10−7 per generation, respectively. It is thought that the high rate of deletion is not related to somatic hypermutation but rather to DNA rearrangement during the heavy-chain class switch, which is occurring in these pre-B cell lines. The point mutation rate was too low to be detected above the background of deletion mutants, less than 5 × 10−8. The immunoglobulin mutator system works weakly, if at all, on two other, nonimmunoglobulin, genes tested: B2m (β2 microglobulin) and the gene for ouabain resistance.Key words: pre-B lymphocyte, B lymphocyte, spontaneous mutation rate, compartmentalization test, deletion mutation, hypermutation.
Alien gene manipulation and expression in wheat
Authors: Gustafson J. P. , Dera A. R.
Published: April 2011

Of the several transformation systems available for plants, only one has proven successful with wheat: alien integration via wide crossing. With the aid of special genetic stocks, alien chromosomes, chromosome arms, or even small segments, have been substituted into wheat. However, the insertion of deleterious genes linked to desirable genes has occurred, and difficulties have been observed in obtaining expression of the inserted alien genes. It is likely that any newly developed transformation system(s) will also experience similar problems. Therefore, research has been expanded into studying the issues associated with transformation. Procedures have been developed that indicate not only the presence of alien genes, but also their physical location. Techniques are also available for analyzing the levels of alien gene expression in wheat.Key words: wheat, aneuploidy, restriction fragment length polymorphism.
Applications of genetic markers in cytogenetic manipulation of the wheat genomes
Authors: Gale M. D. , Sharp P. J. , Chao S. , Law C. N.
Published: April 2011

A molecular map of wheat, Triticum aestivum, is being developed. Problems associated with the large genome size, the large number of linkage groups, polyploidy, and limited polymorphism at the DNA level are being overcome. In addition to the breeding applications expected from the map, various uses for restriction fragment length polymorphism markers as tools in cytogenetic manipulation of wheat chromosomes and those from related species are being found. These include identification of aneuploid genotypes, added precision in intervarietal chromosome manipulations, tests of chromosome stability, identification of alien chromosomes, and marker-aided introgression of genes of agronomic importance from related species.Key words: wheat, restriction fragment length polymorphism, genetic maps, aneuploidy, alien chromosomes.
The potential for rapid speciation in plants
Authors: Macnair Mark R.
Published: April 2011

Speciation involves both ecological adaptation and reproductive isolation. This paper reviews various ways in which plants could achieve reproductive isolation as a direct result of adaptation to prevailing conditions, particularly through changes in flowering time, the adoption of self-fertilization, and changes in flower morphology so that different pollinators are attracted. These characters are likely to have a relatively simple genetic architecture, and there must frequently be genetic variance for them in natural populations. It is argued that speciation could thus be initiated swiftly in plants, without any need for a "genetic revolution" or the fixation of genes with strongly epistatic interactions. Postmating barriers also often have a simple genetic basis in plants, and so could also evolve swiftly if associated with an adaptive response. The nature of the genetic changes associated with speciation in a number of recent speciation events in Layia, Stephanomeria, and Mimulus is reviewed.Key words: Speciation, adaptation, reproductive isolation.
Evolution and ageing
Authors: Kirkland James L.
Published: April 2011

Did senescence evolve as a direct result of natural selection in order to limit the life-span or did increases in longevity evolve in the face of random events that ordinarily limit the life-span? The adaptive hypothesis is that senescence is a programmed process which appeared in evolution because a limited life-span has selective advantages for certain species. Non-adaptive theorists hold that evolution has acted to lengthen the life-span and maximize reproduction and that senescence is only an evolutionary by-product since natural selection does not act directly on postreproductive events. The assumptions and arguments underlying these hypotheses are examined critically in the light of experimental evidence. While theoretical study of the evolution of ageing may advance our understanding of the nature of ageing itself, it is likely that further clarification of the relationship between evolution and ageing will depend on experimental approaches that are now becoming possible.Key words: ageing, senescence, life history, evolution.
Control of gene expression by oligonucleotides covalently linked to intercalating agents
Authors: Hélène Claude , Thuong Nguyen T.
Published: April 2011

Oligodeoxynucleotides covalently linked to intercalating agents selectively recognize the complementary sequence of the oligonucleotide. The intercalating agent provides an additional binding energy which stabilizes the complex. These substances can be used in vitro to block mRNA translation. In cell cultures they are able to inhibit the cytopathic effect of viruses, such as influenza virus and the oncogenic virus SV40. They kill trypanosomes in culture as a result of protein synthesis inhibition. A reactive group can be attached to an oligodeoxynucleotide in order to achieve site-directed modifications of the target sequence. Metal complexes of EDTA, phenanthroline or porphyrins induce cleavage reactions of the phosphodiester backbone in both DNA and RNA. Photoactive groups can be used to modify bases in the complementary sequence. The double helix can be recognized and modified by oligonucleotides that bind to the major groove, forming a local triple helix. These site-directed modifications may inhibit biological processes. The oligonucleotide can be made resistant to nuclease digestion by substituting the synthetic α-anomers of nucleosides to the natural β-nucleosides. These results provide the basis for the design of gene-specific inhibitors that can be used as tools in molecular and cellular biology. They also suggest new approaches for the rational development of selective anti-viral, anti-parasitic, and anti-tumoral agents.Key words: oligonucleotides, intercalating agents, α-nucleosides, DNA cleavage, triple helix, photo cross-linking.
Homologous recombination in prokaryotes: enzymes and controlling sites
Authors: Smith Gerald R.
Published: April 2011

A common step in prokaryotic recombination appears to be the synapsis of the 3′-end of single-stranded DNA with duplex DNA to form a D-loop. The enzymatic mechanisms by which 3′-ends are produced and by which D-loops are converted into recombinant molecules are illustrated by proposed mechanisms of recombination by the Escherichia coli RecBCD pathway and the phage λ Red pathway. The enzymes promoting recombination and the special DNA sites at which they act are emphasized. Recombination by other E. coli pathways and in other prokaryotes is compared with these mechanisms.Key words: Escherichia coli RecBCD pathway, phage λ Red pathway, Chi and cos sites, recombination enzymes.
Direct measurement of mutational spectra in humans
Authors: Thilly William G. , Liu Vivian F. , Brown Bennett J. , Cariello Neal F. , Kat Alexandra G. , Keohavong Phouthone
Published: April 2011

By combining high fidelity in vitro DNA amplification and mutant DNA sequence separation by denaturing gradient gel electrophoresis, we are able to directly observe mutational hotspots in human genomic DNA. Our technological development has progressed through the stage of identifying mutant sequences in independently derived, 6-thioguanine-resistant human B cells. We are now analyzing uncloned, complex populations derived from several thousand 6-thioguanine-resistant cells and report preliminary data concerning the mutational spectra of benzo[a]pyrene diol epoxide and ultraviolet light in exon 3 of the hypoxanthine-guanine phosphoribosyltransferase gene. In addition, the approach appears to be general for any gene sequence for which a means to select mutants exists. The more global need to eliminate phenotypic selection is, however, our primary impetus. Our analysis leads us to conclude that no known in vitro DNA polymerase has sufficient fidelity to permit direct observation of unselected mutants. Therefore, an additional change in technology will be necessary to observe nonselected mutant DNA sequences at the low frequencies found in human tissues.Key words: mutational spectra, polymerase chain reaction, denaturing gradient gel electrophoresis.
The structure and function of RAD6 and RAD18 DNA repair genes of Saccharomyces cerevisiae
Authors: Prakash Louise
Published: April 2011

The RAD6 and RAD18 genes of Saccharomyces cerevisiae are required for postreplication repair of discontinuities occurring in newly synthesized DNA following exposure to uv light. In addition, rad6 mutants are highly defective in mutagenesis induced by uv and other DNA damaging agents and in sporulation. RAD6 encodes a protein of 172 amino acids with a highly acidic carboxyl terminus. Deletion of the carboxyl terminal 23 residues, 20 of which are acidic, has little or no effect on uv sensitivity or uv mutagenesis, but sporulation is greatly reduced. Addition of the first four residues of the polyacidic tail restores sporulation to 50% the level observed in RAD+/RAD+ diploids. RAD6 protein has been previously shown to be a ubiquitin-conjugating (E2) enzyme that attaches ubiquitin to histones H2A and H2B in vitro. Our experiments show that deletion of varying lengths of the polyacidic tail of RAD6 protein greatly reduces its ubiquitin-conjugating activity. The RAD18 encoded protein contains features which suggest that it binds DNA and nucleotides. Ten of the 12 cysteine residues occur in regions that could form zinc finger domains for nucleic acid binding. The other interesting feature in RAD18 protein is the presence of a putative nucleotide binding sequence. The possible in vivo functions of the RAD6 and RAD18 proteins are discussed.Key words: yeast, polyacidic tail, zinc fingers, uv damage.
Genetic investigation of salt reception in Drosophila melanogaster
Authors: Siddiqi Obaid , Joshi Swati , Arora Kavita , Rodrigues Veronica
Published: April 2011

We have used mutants defective in gustatory behavior to investigate the neural basis of salt perception in the fruitfly Drosophila melanogaster. Salts elicit responses from two sensory neurons, L1 and L2, in each taste sensillum. Results from competition tests, selective proteoloysis, and mutant studies lead us to speculate that L1 possesses two sites (A and B) for the detection of monovalent ions. The A site accepts Na+ ions alone, while the B site is less selective responding to Na+, K+, and Li+. The loss of the A-mediated response in the mutant gustE leads to a concomitant reduction in its behavioral attraction to NaCl. This suggests that the L1 neuron signals attraction to low concentrations of NaCl. This inference is supported by examining the kinetics of behavioral and electrophysiological responses in the wild type and in mutants that show enhanced attraction to salts.Key words: gustatory mutants, Drosophila, salt sites, preference test.
Molecular mechanisms of regulation of HTLV-1 gene expression and its association with leukemogenesis
Authors: Yoshida Mitsuaki , Inoue Junichiro , Fujisawa Junichi , Seiki Motoharu
Published: April 2011

Human T-cell leukemia virus type 1 (HTLV-1) has two trans-acting regulator genes, tax and rex, in the pX region. The tax gene is a trans-acting transcriptional activator of the long terminal repeat (LTR) and also of the cellular gene for IL-2Rα. The latter seems to explain initiation of abnormal growth of HTLV-1 infected cells. The rex gene is a posttranscriptional regulator accumulating gag and env mRNA and also indirectly suppressing the transcription. The regulation requires two cis-acting elements, the LTR sequence at the 3′ terminus and 5′ splice signal, suggesting a novel mechanism of RNA processing in the nucleus. These two trans-activator genes are essential for efficient replication of HTLV-1 and also explain its poor replication competence and tendency to be latent in vivo.Key words: HTLV-1, trans-activation, posttranscriptional regulation, RNA splicing.
The 93D heat shock locus of Drosophila melanogaster: modulation by genetic and developmental factors
Authors: Lakhotia S. C.
Published: April 2011

The 93D locus in Drosophila melanogaster and the 93D-like loci in other species of Drosophila, collectively termed hsr ω (heat shock RNA omega) locus, display several unique and intriguing features: (i) developmental regulation and selective induction by several agents like benzamide, colchicine, thiamphenicol, vit-B6; (ii) functional conservation in the genus but a very rapid DNA base sequence divergence; (iii) in spite of the rapid DNA sequence divergence, a strong conservation of organization (a 5′ unique region and a 3′ long tandem repeat region) and the pattern of multiple ω transcripts in the genus; (iv) a general nontranslatability of all the three major species of ω transcripts (an ~ 10-kb ω1, a 2.0-kb ω2, and a 1.2-kb ω3 species) although some recent evidence favours translatability of a small open reading frame (~ 23 – 27 amino acid long) in the ω3 transcript; (v) dispensability of the hsr ω locus for heat shock protein synthesis but indispensability for viability of flies. The heat shock inducibility of the 93D locus of D. melanogaster is selectively repressed by (i) combination of heat shock with another inducer of 93D; (ii) rearing of larvae at 10 °C; (iii) heterozygous deficiency for the 93D region; and (iv) conditions that alter levels of beta-alanine. In all cases of repression of the 93D locus during heat shock, the 87A and 87C loci (the two duplicate loci harbouring multiple copies for hsp70 and the alpha–beta repeat sequences (at 87C)) develop unequal puffs. The hsr ω locus appears to be under a complex system of regulation involving autoregulation as well as regulation by other factors in the cell which possibly operate through different control elements on the locus.Key words: benzamide, colchicine, beta-alanine, hsr ω, heat shock puffs, Drosophila.
The evolution of growth trajectories and other complex quantitative characters
Authors: Kirkpatrick Mark , Lofsvold David
Published: April 2011

Growth trajectories differ from many other quantitative, characters in that they are characterized by a continuous function rather than by a finite number of discrete measurements. We review here recently developed methods for predicting the evolution of growth trajectories under the influence of natural or artificial selection. Using our method, analysis of genetic data from mice shows that the patterns of genetic variation arising from developmental processes impose constraints on evolution of growth trajectories. These constraints can be quantified to reveal the families of growth trajectories that can be produced by selection and those families that cannot. The data suggest there may be relatively few evolutionary degrees of freedom for growth trajectories despite the presence of abundant additive genetic variation to alter size and (or) growth rate at every age. The description of these constraints may be useful to both biologists who would like to determine the evolutionary options available to natural populations and to breeders who would like to alter growth trajectories to economically improve domesticated species. Our methods and conclusions can be generalized to other kinds of "infinite-dimensional" or complex characters, including morphological shapes and norms of reaction.Key words: growth trajectories, quantitative genetics, constraints, infinite-dimensional characters, body size.
In vitro methods of germ-plasm conservation
Authors: Roca W. M. , Chavez R. , Martin M. L. , Arias D. I. , Mafla G. , Reyes R.
Published: April 2011

For many crops with preferential vegetative propagation, or which are sterile, or have seed unresponsive to standard seed storage techniques, in vitro methods can provide a valuable adjunct to other germ plasm conservation strategies. Two types of in vitro gene banks are proposed: (i) an in vitro active gene bank where cultures are maintained under slow growth; of the few of these that exist, the cassava (Manihot) in vitro active gene bank of the Centro Internacional de Agricultura Tropical (CIAT) consists of over 4000 clones; (ii) an in vitro base gene bank, where cultures are cryopreserved; at present, none of this type exist. In vitro conservation offers a means of maintaining valuable gene combinations in a small space, protected against pest and disease attack, soil problems, and climatic changes, and with high multiplication potential. The main limitations are inability to regenerate plants of many important crops and the risk of genetic instability of cultures. A joint project of the International Board for Plant Genetic Resources and CIAT is underway to develop an in vitro based set of procedures for handling germ plasm, using cassava as a model, with culture maintenance, stability monitoring, and management data bases being considered. Results of recent work on in vitro conservation and related activities, i.e., germ-plasm collection, exchange, and characterization, will be presented and discussed, with special reference to Manihot.Key words: in vitro gene banks, cryopreservation, isozyme electrophoresis, genotype stability, Manihot esculenta Crantz.
Potential DNA methods for measuring the human heritable mutation rate
Authors: Mendelsohn Mortimer L.
Published: April 2011

Potential methods are reviewed for estimating human heritable mutation rates by comparing the DNA of parents and offspring. In the 4 years since the Alta Workshop on this subject, information has accumulated on several of the six methods detailed in that meeting. Some of the methods now appear to be infeasible, and all continue to be too inefficient for practical implementation. Newer DNA approaches are discussed, including several that could become practical enough for implementation. Finally, DNA-oriented methods using human sperm are considered as possible alternatives to the heritable approaches.Key words: human heritable mutation, human mutation rate, DNA method – DNA technology, radiation.
Eugenics and American social history, 1880–1950
Authors: Allen Garland E.
Published: April 2011

Eugenics, the attempt to improve the human species socially through better breeding was a widespread and popular movement in the United States and Europe between 1910 and 1940; Eugenics was an attempt to use science (the newly discovered Mendelian laws of heredity) to solve social problems (crime, alcoholism, prostitution, rebelliousness), using trained experts. Eugenics gained much support from progressive reform thinkers, who sought to plan social development using expert knowledge in both the social and natural sciences. In eugenics, progressive reformers saw the opportunity to attack social problems efficiently by treating the cause (bad heredity) rather than the effect. Much of the impetus for social and economic reform came from class conflict in the period 1880–1930, resulting from industrialization, unemployment, working conditions, periodic depressions, and unionization. In response, the industrialist class adopted firmer measures of economic control (abandonment of laissez-faire principles), the principles of government regulation (interstate commerce, labor), and the cult of industrial efficiency. Eugenics was only one aspect of progressive reform, but as a scientific claim to explain the cause of social problems, it was a particularly powerful weapon in the arsenal of class conflict at the time.Key words: eugenics, social genetics.
The biology and exploitation of the retrotransposon Ty in Saccharomyces cerevisiae
Authors: Garfinkel David J. , Curcio M. Joan , Youngren Susan D. , Sanders Nancy J.
Published: April 2011

Retrotransposons are a widely distributed group of eukaryotic mobile genetic elements that transpose through an RNA intermediate. The element is transcribed into RNA, and this RNA is reverse transcribed into a DNA copy capable of insertion into many different chromosomal locations. Maturation of proteins and reverse transcription take place within noninfectious intracellular viruslike particles. We have studied the element Ty, which is found dispersed in the genome of the yeast Saccharomyces cerevisiae. The frequency of Ty element transposition is normally quite low but can be greatly increased by expressing an element from a strong promoter. We have used the ability to control the level of Ty transposition to investigate the functions of Ty proteins, the regulation of Ty transposition, and the exploitation of Ty elements as insertional mutagens in yeast. The information gained from these experiments should be applicable to the study of retrotransposons found in multicellular organisms.Key words: yeast, Saccharomyces cerevisiae, transposons, Ty elements, mutagenesis.
Automated DNA sequencing and the analysis of the human genome
Authors: Smith Lloyd M.
Published: April 2011

The Human Genome Initiative is a complex, multifaceted, international effort to establish a massive data base of map and sequence information for humans and other organisms. The success of this initiative is dependent upon the development of new technologies for the analysis of genomes. In this paper, an overview of the Human Genome Initiative is presented, and the current status of efforts to automate large-scale DNA sequence analysis is reviewed.Key words: DNA sequencing, human genome, automated sequencing.
Cloning of sheep and cow embryos
Authors: Willadsen Steen M.
Published: April 2011

The results of experiments aimed at cloning of sheep and cattle embryos are described. Two experimental approaches were used to study the developmental potential of blastomeres from sheep and cow embryos: (i) blastomere separation followed by culture and (ii) fusion of isolated blastomeres with enucleated eggs followed by culture. Both approaches allow embryos to be cloned, but whereas blastomere separation allows only a relatively small number of genetically identical animals to be produced, nuclear transplantation will probably open the way for large-scale cloning of livestock.Key words: sheep, cow, cloning, blastomere separation, nuclear transplantation.
Potato breeding with haploids and 2n gametes
Authors: Peloquin S. J. , Yerk Georgia L. , Werner Joanna E. , Darmo Elizabeth
Published: April 2011

Potato breeding methods that utilize haploids of Solanum tuberosum group Tuberosum or group Andigena and 2n gametes exploit the genetic diversity, including both valuable traits and allelic diversity, available in exotic germ plasm. Three essential components are involved: (i) the wild and cultivated 2x relatives of the cultivated 4x potato are a valuable source of genetic diversity; (ii) haploids (2n = 2x = 24) of cultivars (2n = 4x = 48) are effective in capturing diversity (germ plasm enhancement); (iii) 2n gametes, resulting from first division restitution, are an efficient method of transmitting this genetic diversity to cultivated 4x potatoes. Heterosis for total and marketable tuber yield and specific gravity occurs in 4x families from crosses between 4x cultivars and 2x haploid Tuberosum × 'Phureja' hybrids. Selected 4x clones from relatively small 4x × 2x families have been released as cultivars based on their earliness and heat tolerance in the tropics. Other 4x clones from 4x × 2x crosses, where the 2x parents were haploid – wild species hybrids, have good yield, excellent tuber type, high specific gravity, low reducing sugars, storage quality, and stress tolerance. The seedling vigor, uniformity, and large tuber yields of progeny from 4x × 2x crosses also makes this an effective breeding method for producing potatoes from true potato seed. This breeding method is also being successfully exploited in alfalfa, red clover, sweet potatoes, yams and several species of grasses, fruits, and ornamentals.Key words: potato, haploids, 2n gametes, germ plasm, allelic diversity.
Constructing chromosome- and region-specific cosmid maps of the human genome
Authors: Carrano A. V. , Jong P. J. de , Branscomb E. , Slezak T. , Watkins B. W.
Published: April 2011

A chromosome-specific ordered set of cosmids would be a significant contribution toward understanding human chromosome structure and function. We are developing two parallel approaches for creating an ordered cosmid library of human chromosome 19 and other selected subregions of the human genome. The "bottom up" approach is used to establish sets of overlapping cosmids as islands or "contigs" along the chromosome, while the "top down" approach, using pulsed-field gel electrophoresis and yeast cloning, will establish a large-fragment map and close the inevitable gaps remaining from the "bottom up" approach. Source DNA consists of a single homolog of chromosome 19 from a hamster–human hybrid cell and human fragments cloned in yeast artificial chromosomes. We have constructed cosmid libraries in a vector that facilitates cloning small amounts of DNA, allows transcription of the insert termini, and contains unique sites for partial-digest mapping. Computer simulations of cosmid contig building suggest that near-optimal efficiency can be achieved with high-density restriction fragment digest schemes that can detect 20–30% overlap between cosmids. We developed the chemistry and data analysis tools to compare the ordering efficiencies of several cosmid restriction digest fingerprinting strategies. Restriction fragments from a four-cutter digest are labeled with a fluorochrome, separated by polyacrylamide gel electrophoresis, and detected after laser excitation as they traverse a fixed point in the gel. We have also developed the software to rapidly process the output signal to define and analyze the fragment peaks. Up to three cosmids (or three different digests of the same cosmid) plus a size standard are analyzed simultaneously in a single gel lane. In two pilot experiments, cosmid contig maps from a small region of chromosome 19 and a 600-kilobase region of chromosome 14q21 have been constructed. The resulting maps, when coupled to the known genetic map, provide a collection of cloned cosmids for further study.Key words: human, genome, cosmid, fingerprinting, DNA, electrophoresis, contig, automation, restriction enzyme.
Genetic control of cold hardiness and vernalization requirement in rye
Authors: Brule-Babel A. L. , Fowler D. B.
Published: April 2011

Rye (Secale cereale L.) is recognized as the most cold-tolerant winter cereal species. However, little is known of the genetic control of cold hardiness and its interaction with vernalization requirement in rye. In the present study, the modes of inheritance of cold hardiness and vernalization requirement were investigated in crosses among one spring and two winter rye cultivars that represented a wide range of winter survivability. Differences in growth habit were found to be determined by a single dominant gene for the spring growth habit. Multiple alleles, or modifiers, for this major gene may also have been present. Cold hardiness was controlled by genes with mainly additive effects, but other factors may also have been involved. Cytoplasmic effects were not detected. Broad-sense heritability estimates were generally high (48–82%), indicating that selection for cold hardiness should be effective in breeding programs.Key words: Secale cereale L., dominance, additive gene action, heritability, cytoplasmic effects.
Q-band chromosomal polymorphisms in arctic char (Salvelinus alpinus)
Authors: Pleyte Kay A. , Phillips Ruth B. , Hartley Sheila E.
Published: April 2011

Stock-specific variation in the number and location of quinacrine-staining chromosomal bands was found in North American and European stocks of arctic char (Salvelinus alpinus). The mean number of bands per genome varied from 5.8 ± 5.3 in the Northwest Territories stock to 15.4 ± 2.1 in the Scottish stock. These bands appear to represent a subset of heterochromatin since they stain darkly with the C-band technique. Since the four stocks examined were each distinguishable on the basis of their Q-band patterns, these chromosome markers should be useful in genetic comparisons between different arctic char stocks and populations.Key words: Q banding, chromosomes, polymorphisms, arctic char, Salvelinus alpinus.