bluuebunny/crossref_metadata_2025 huggingface dataset:
Altered gene expression during cellular aging
Authors: Smith James R. , Pereira-Smith Olivia M.
Published: April 2011

The limited division potential of normal human diploid fibroblasts in culture represents a model system for cellular aging. Observations indicate cellular senescence is an active process. Senescent cells, although unable to divide, are actively metabolizing. Hybrids from fusion of normal and immortal human cells exhibit limited division potential, suggesting that the phenotype of cellular senescence is dominant and supporting the hypothesis that senescence is genetically programmed. Fusion of immortal human cell lines with each other has identified four complementation groups for indefinite division. This indicates that a limited number of specific genes or processes are involved in senescence. Senescent cells express highly abundant DNA synthesis inhibitory messenger RNAs and produce a surface membrane associated protein inhibitor of DNA synthesis not expressed in young cells. Senescent cell membranes were used as immunogen to generate three monoclonal antibodies reacting specifically with senescent but not young cells in several normal human cell lines. We have also found that fibronectin messenger RNA accumulates to high levels in senescent cells. The role of these changes in gene expression in senescence is being explored.Key words: cellular senescence, human cells.
Genetic modulation of the senescent phenotype in Homo sapiens
Authors: Martin George M.
Published: April 2011

While it is important to search for unifying mechanisms of aging among a variety of model systems, evolutionary arguments suggest that the pathophysiological details of senescence may be, to some extent, species specific. Moreover, in species that are characterized by extensive genetic heterogeneity, such as our own, one is likely to find kindreds with both "private" and "public" markers of aging. Crude estimates of the number of loci with the potential to modulate aspects of the senescent phenotype of man suggest that thousands of genes could be involved. No single locus appears to modulate all features. Some affect predominately a single aspect ("unimodal progeroid syndromes"); familial Alzheimer's disease is discussed as a prototype. Linkage studies indicate genetic heterogeneity for autosomal dominant forms of the disease. Some loci affect multiple aspects of the phenotype ("segmental progeroid disorders"); the prototype is Werner's syndrome, an autosomal recessive. Cells from homozygotes behave like mutator strains and undergo accelerated senescence in vitro. Elucidation of the biochemical genetic basis of such abiotrophic disorders may shed light on specific aging processes in man.Key words: Homo sapiens, senescence, progeroid syndromes, Alzheimer's disease, linkage, Werner's syndrome, mutator strains.
Genetic analysis of the N transcription antitermination system of phage λ
Authors: Friedman David I. , Granston Andrew E. , Thompson Debra , Schauer Alan T. , Olson Eric R.
Published: April 2011

Regulation of coliphage λ gene expression occurs, in part, by a process of termination and antitermination of transcription. The N gene product, one of two λ encoded antitermination proteins, acts with host encoded proteins, Nus, at sites, nut, located downstream of the early promoters to render the transcribing RNA polymerase resistant to many downstream termination signals. We discuss the nature of some of the proteins and sites involved in this process.Key words: regulation, transcription, termination, antitermination, nusA, N, boxA, nut.
Protein:DNA interactions at chromosomal loop attachment sites
Authors: Blasquez Veronica C. , Sperry Ann O. , Cockerill Peter N. , Garrard William T.
Published: April 2011

We have recently identified an evolutionarily conserved class of sequences that organize chromosomal loops in the interphase nucleus, which we have termed "matrix association regions" (MARs). MARs are about 200 bp long, AT-rich, contain topoisomerase II consensus sequences and other AT-rich sequence motifs, often reside near cis-acting regulatory sequences, and their binding sites are abundant (> 10 000 per mammalian nucleus). Here we demonstrate that the interactions between the mouse κ immunoglobulin gene MAR and topoisomerase II or the "nuclear matrix" occur between multiple and sometimes overlapping binding sites. Interestingly, the sites most susceptible to topoisomerase II cleavage are localized near the breakpoints of a previously described illegitimate recombination event. The presence of multiple binding sites within single MARs may allow DNA and RNA polymerase passage without disrupting primary loop organization.Key words: MARs, chromatin loops, topoisomerase II, nuclear matrix.
Tissue-specific activity of the pro-opiomelanocortin (POMC) gene and repression by glucocorticoids
Authors: Drouin Jacques , Nemer Mona , Charron Jean , Gagner Jean-Pierre , Jeannotte Lucie , Sun Yu Lin , Therrien Marc , Tremblay Yves
Published: April 2011

The gene encoding pro-opiomelanocortin (POMC) is specifically expressed in two different cell types of the pituitary gland. We have defined the regulatory DNA sequences of the POMC gene that are responsible for this cell-specific expression. In addition, we have defined a regulatory element, located in the proximal region of the POMC promoter, that confers glucocorticoid repression in the anterior pituitary. Using DNA-mediated gene transfer into transgenic mice and tissue culture cells, the POMC regulatory sequences required for cell-specific expression and glucocorticoid repression were localized within a 543-bp fragment in the 5′-flanking region of the gene. Multiple regulatory elements that bind nuclear proteins are present within this region. In particular, a sequence that binds the glucocorticoid receptor and behaves as a "negative glucocorticoid response element"; (nGRE) also binds nuclear proteins of the COUP (chicken ovalbumin upstream promoter) family of transcription factors. Thus, glucocorticoid repression of POMC transcription may result from the mutually exclusive binding of the glucocorticoid receptor and the COUP transcription factor to the POMC nGRE.Key words: pro-opiomelanocortin, steroid hormone action, repression, tissue-specific expression.
Intermediates in homologous recombination revealed by marker effects in Ascobolus
Authors: Nicolas Alain , Rossignol Jean-Luc
Published: April 2011

This paper reviews our current knowledge on the molecular mechanisms of meiotic recombination in the filamentous fungus Ascobolus immersus.Key words: Ascobolus, meiotic recombination, heteroduplex DNA, crossing-over, marker effects.
Recombination in yeast and the recombinant DNA technology
Authors: Petes Thomas D. , Detloff Peter , Jinks-Robertson Sue , Judd S. Renee , Kupiec Martin , Nag Dilip , Stapleton Ann , Symington Lorraine S. , Vincent Annette , White Michael
Published: April 2011

The development of methods to isolate eukaryotic genes, alter these genes in vitro and reintroduce them into the cell has had a major impact on the study of recombination in the yeast Saccharomyces cerevisiae. In this paper we discuss how recombinant DNA techniques have been employed in the study of recombination in yeast and the results that have been obtained in these studies.Key words: recombination, Saccharomyces cerevisiae, gene conversion, repeated genes.
Major sex-determining genes and the control of sexual dimorphism in Caenorhabditis elegans
Authors: Hodgkin Jonathan , Chisholm Andrew D. , Shen Michael M.
Published: April 2011

Sex determination in Caenorhabditis elegans involves a cascade of major regulatory genes connecting the primary sex determining signal, X chromosome dosage, to key switch genes, which in turn direct development along either male or female pathways. Animals with one X chromosome (XO) are male, while animals with two X chromosomes (XX) are hermaphrodite: hermaphrodite development occurs because the action of the regulatory genes is modified in the germ line so that both sperm and oocytes are made inside a completely female soma. The regulatory genes are being examined by both genetic and molecular means. We discuss how these major genes, in particular the last switch gene in the cascade, tra-1, might regulate the many different sex-specific events that occur during the development of the hermaphrodite and of the male.Key words: nematode, Caenorhabditis elegans, sex determination, sexual differentiation, cell lineage analysis.
Expression of members of the Saccharomyces cerevisiae hsp70 multigene family
Authors: Werner-Washburne Margaret , Craig Elizabeth A.
Published: April 2011

The hsp70 multigene family of Saccharomyces cerevisiae is a complex multigene family, composed of members exhibiting complex patterns of regulation. Expression of some members is induced after a heat shock, whereas expression of others is repressed. Some members of the family are expressed during exponential growth. One gene, SSA3, shows an unusual pattern of expression during approach to stationary phase. While most RNAs decrease in abundance, SSA3 RNA levels dramatically increase. The constitutive expression of SSA3 in cells lacking adenylate cyclase activity suggests that cAMP modulates SSA3 expression.Key words: heat shock proteins, S. cerevisiae, cAMP, gene expression, stress seventy genes.
Maintenance of genetic variability by mutation–selection balance: a child's guide through the jungle
Authors: Bulmer M. G.
Published: April 2011

Metric characters closely connected with fitness have little additive genetic variability, presumably because it is quickly exhausted under continuous directional selection on fitness. Other metric characters have substantial additive genetic variability with a typical heritability of about 0.5. A popular model is that the second class of characters is subject to weak stabilizing selection for an optimal value, which depletes genetic variability, while recurrent mutation tends to restore it. Can this model account for the variability observed, given the evidence available about the strength of selection and mutation rates? Much theoretical work has been done on this complex problem. This work is reviewed, with the intention of simplifying it as much as possible.Key words: mutation–selection balance, genetic variability, continuum-of-alleles model, house-of-cards approximation.
Molecular population genetics of structural variants of esterase 6 in Drosophila melanogaster
Authors: Oakeshott J. G. , Cooke P. H. , Richmond R. C. , Bortoli A. , Game A. Y. , Labate J.
Published: April 2011

Several lines of evidence indicate that natural selection operates between the major EST6-F and EST6-S allozymes of Drosophila melanogaster. In particular, consistent latitudinal clines and seasonal variation in their relative frequencies strongly suggest that they are not selectively equivalent in field populations. Several laboratory studies have found frequency-dependent fitness differences among the Est6-F and Est6-S genotypes. Moreover, the purified EST6-F and EST6-S allozymes differ in biochemical properties and the physiology of the enzyme, as a major component of the seminal fluid, suggests that these differences could affect reproductive aspects of fitness. However, molecular analyses reveal high levels of variation in the EST6 protein both within and between the EST6-F and EST6-S allozymes. Limited thermostability and more sensitive electrophoretic analyses reveal at least 17 variants of the two allozymes and sequence comparisons among 13 isolates of the Est6 gene reveal 16 nucleotide polymorphisms that would lead to amino acid differences. Two closely linked amino acid differences are strongly associated with the major difference between EST6-F and EST6-S; either or both of these are likely to cause the observed biochemical differences between EST6-F and EST6-S and may be the primary targets for the selection between these allozymes. The functional and adaptive significance of the other amino acid polymorphisms is unclear, although the data suggest that the EST6-8 haplotype within EST6-S has both arisen and proliferated relatively recently.Key words: Drosophila melanogaster, esterase 6, nucleotide and amino acid polymorphism, natural selection.
Core collections: a practical approach to genetic resources management
Authors: Brown A. H. D.
Published: April 2011

Large numbers of entries are now lodged in many of the world's germ-plasm collections of crop and pasture plants. This abundance of material, assembled to guard against its irretrievable loss, has intensified the problems of how best to conserve it and how to use it in plant breeding. Core collections have a major role to play in solving these problems. The core is composed of about 10% of the total collection, chosen to represent as much as possible of the diversity in the collection. The selection of the core entries should use the available data on the geographic origin, the genetic characteristics, and the possible value to breeders and other users of each accession in the collection. Stratified sampling from groups of accessions, in logarithmic or absolute proportion to the group size, is the best strategy. The core entries should be kept separately and not in one bulk population. The composition of the core should be adjusted as new material is included, or better data are obtained. The remaining accessions in the collection form the reserve, which should be conserved as secondary sources.Key words: germ-plasm collections, sampling strategies, Glycine tomentella, Hordeum vulgare.
Politics of heredity — Germany 1900–1940, a brief overview
Authors: Weingart Peter
Published: April 2011

The paper gives a brief overview of the main stages of development of eugenics and race hygiene in Germany between 1900 and 1940. Two main stages can be differentiated: one, the formation of the eugenics movement and its development parallel to quantitative population policy before and after World War I, and the second beginning toward the end of the Weimar Republic (1919–1933) when the financial crisis of the public health system favored eugenic schemes implemented by an authoritarian government, such as the Nazi regime.Key words: eugenics, race hygiene, Germany, quantitative population policy, World War I, Nazi regime.
Transgenic mice
Authors: Babinet C. , Morello D. , Renard J. P.
Published: April 2011

Stable integration into the mouse genome of exogenous genetic information has become, over the past few years, a very potent approach for different aspects of biology. It is a common feature that the integrated exogenous gene (the transgene) is expressed properly both spatially and temporally. Constructing different lines of transgenic mice carrying various versions of a gene, therefore, permits cis acting DNA sequences involved in the specificity of expression to be defined, in the context of the developing animal. This in turn opens the way to a variety of experiments in which a given gene product is targeted to one or another cell type, thus offering some insight into the physiological role of this product. Such a strategy has been used, for example, to address the questions of the role of oncogenes in malignant transformation. The insertion of foreign DNA per se may disrupt the function of endogenous genes, thus creating an insertional mutation. The corresponding affected genes may subsequently be cloned, using the transgene as a tag. Finally, the ability to perform homologous recombination, recently demonstrated with embryonic stem cells that can colonize the germ line of a foreign embryo, should constitute in the near future a unique way to analyse in detail the functioning of the mammalian genome.Key words: transgenic mice, oncogenes, insertional mutagenesis, cis-acting sequences, homologous recombination.
Agrobacterium-mediated gene transfer to monocots and dicots
Authors: Hohn Barbara , Koukolíková-Nicola Zdena , Bakkeren Guus , Grimsley Nigel
Published: April 2011

The interaction of the soil bacterium Agrobacterium tumefaciens with plants constitutes a unique kind of genetic flux: the bacterium transfers the T-DNA part of its Ti plasmid to plant cells, where it is integrated into the genome. Possible transfer intermediates, isolated from bacteria and from plants early after transfer, are described. Agroinfection, Agrobacterium-mediated delivery of plant viral genomes, is employed to monitor early events in T-DNA transfer in dicot plants. Graminaceous monocots, so far excluded from Agrobacterium's host range because of lack of tumor formation, have been shown to be agroinfectable. This newly discovered interaction between grasses and the pathogen is described in terms of the efficiency of gene transfer as compared with dicot hosts, the involvement of the bacterium's virulence genes, the susceptibility of various developmental stages of the host, the implications for biotechnology, and the evolutionary aspects of this host–parasite relationship.Key words: T-DNA, agroinfection, maize streak virus, plant transformation, Zea mays.
Evolving strategies for making physical maps of mammalian chromosomes
Authors: Smith Cassandra L. , Cantor Charles R.
Published: April 2011

Two types of physical maps are described: restriction maps made by top down approaches using enzymes that cut the genome infrequently, and complete libraries, made by bottom up approaches using fingerprinting of randomly selected cloned DNA. Construction of such maps for mammalian chromosomes is complicated by the mosaic nature of mammalian genomes, and extensive polymorphisms at the cleavage sites of most enzymes that yield large DNA fragments. However, it appears that both of these potential difficulties can be turned into advantages by new mapping strategies. When combined with yeast artificial chromosome cloning and polymerase chain reaction amplification methods, these approaches should soon yield complete maps of many human chromosomes.Key words: fingerprinting, restriction maps, DNA polymorphisms, human genome.
New technologies for large-genome sequencing
Authors: Martin William J.
Published: April 2011

Interest in DNA sequencing has increased in recent years and research into new instrument systems to optimize and automate the process has been intensified. A number of commercial devices, from Europe, Japan, and the United States, which instrument aspects of (mainly) the Sanger method, are now available and several new DNA sequencing techniques have been reported. This review briefly describes current methods of DNA sequencing and provides an account of systems presently available or under development for instrumenting the technology. The problems of automation for large-scale DNA sequencing are discussed.Key words: sequencing, automation, genome, DNA, instrumentation.
Karyotype divergence in Symphodus melops and Symphodus roissali (Labridae, Perciforms): C-banded and Ag-NOR karyotypes
Authors: López J. R. , Alvarez M. C. , Thode G. , Martinez G.
Published: April 2011

A comparative analysis of conventional C-banded and Ag-NOR karyotypes involving the closely related labrid species Symphodus melops and Symphodus roissali showed conspicuous differences between them, reflected mainly in their 2n and fundamental number values. The chromosome rearrangements apparently involved consisted of three centric fusions, pericentric inversions, and (or) translocations, as well as small heterochromatic additions. In spite of this clear divergence, the two species seem to have one larger metacentric pair, the nucleolar organizer region (NOR) carrier chromosomes, and some smaller unidentified pairs in common. Both karyotypes are fully representative of the described tendency in the labrids towards symmetric morphology. The NOR regions were shown to have C-banding and a heteromorphism between homologous regions was detected by conventional and silver staining, but not by the C-banding technique, which leads us to suggest that the NOR regions' heteromorphism is functional rather than structural in nature.Key words: Labridae, heterochromatin, nucleolus organizers.
Influence of environments on the development of multivariate structures in a barley composite cross at three locations
Authors: Jana Sakti , Zhang Qifa , Saghai-Maroof Mohammad A.
Published: April 2011

Starting in the F4 generation, successive generations of a barley composite cross (CCXXI) were propagated in three North American locations. Data were collected for seven isozyme loci and 12 morphological characters from three generations (F5, F11, or F12 and F18 or F19) at each location and were analyzed for evolutionary changes of multilocus associations. Rates of change of multilocus gametic frequencies for isozyme loci varied according to location. The changes occurred faster at the temperate northern locations (Saskatoon and Beaverlodge) than at the Mediterranean-type southern (Davis) location, which resulted in a large divergence in genetic composition of the population over a relatively short period. The repatterning of the genomic structure occurred at a faster rate in later generations (between F11 or F12 to F18 or F19) than in earlier generations (between F5 and F11 or F12). Canonical correlation analyses between the two sets of characters (morphological and isozymic) indicated that different structures of covariation evolved in different locations. Our results clearly demonstrate the environmental influence on the evolution of correlated multilocus complexes in experimental barley populations.Key words: Hordeum vulgare, population dynamics, multilocus genotype, canonical correlation analysis, environmental influence, genetic divergence.
Gametic selection during wheat anther culture
Authors: Buyser J. De , Bachelier B. , Henry Y.
Published: April 2011

Gametic selection was investigated in a monosomic 1D line of wheat. Comparison of chromosome numbers in progenies from cross- or self-pollination and anther culture indicated the frequency of the different types of gametes acting in zygote formation. The progenies obtained from reciprocal crosses (monosomic × euploid) were different in terms of frequencies of monosomic plants. All the pollen grains do not have an equal probability of fertilization since a strong gametic selection for euhaploid male gametes was observed when the monosomic line was used as male parent; only 13% of the nullisomic survived to embryogenesis and seed germination. Regenerants from anther culture also demonstrated that the percentage of nullihaploids was reduced, indicating a strong selection for euhaploid gametes. A comparison between the frequency of male nullihaploid gametes in the cross disomic × monosomic and in the anther culture revealed that the two processes generate the same gamete transmission. The in vitro cultures do not induce more selection pressure than the embryogenic development even if they are together biased samples of the male gametic population.
Mechanisms promoting the appearance of abnormal spermatids in B-carrier individuals of Eyprepocnemis plorans (Orthoptera)
Authors: Suja J. A. , Vega C. García de la , Rufas J. S.
Published: April 2011

Males of Eyprepocnemis plorans that carry B chromosomes have been analysed to test for the presence of aberrant spermatids. The study of the behaviour of the B chromosomes throughout meiosis provides some clues for the appearance of some kinds of abnormal spermatids. However, most of these spermatids are assumed to result from the impairment of the maintenance of intercellular bridges early in spermiogenesis. A model to explain these results is presented.Key words: B chromosomes, spermiogenesis, insect spermatogenesis.
A model of meiotic chromosome association in triploids
Authors: Crane Charles F. , Sleper David A.
Published: April 2011

A model was developed for chromosome association at meiotic metaphase I in triploids. Probabilities were estimated for each pachytene configuration and for subsequent formation of at least one chiasma in each combination of chromosome arms. Long and short arms were allowed to differ, but were related through an effective arm ratio so that the pattern of genomic affinity was the same for both arms. No other a priori assumptions were made about the pattern of genomic affinity. However, the usual assumptions of genome analysis were made including the following: identity of genomic-affinity pattern and chiasma frequency across homeologous groups, freedom from translocation heterozygosity, independence of chromosome arms, and absence of chiasma formation on both sides of a synaptic partner exchange within an arm. The model was statistically overparameterized and, therefore, had multiple solutions that yielded the same expected meiotic analysis. The range of these solutions can be found through repeated optimizations from randomly chosen starting values within the permitted ranges of the variables. It was convenient to express the optimized pattern of genomic affinity in terms of the proportions of metaphase I association due to each pairwise combination of genomes. Genomic affinity was analyzed in 16 triploid hybrids with the aid of the model.Key words: polyploidy, genome analysis, meiotic model.
Inheritance of greenbug, Schizaphis graminum (Rondani), virulence to Gb2 and Gb3 resistance genes in wheat
Authors: Puterka Gary J. , Peters Don C.
Published: April 2011

The inheritance of greenbug, Schizaphis graminum (Rondani), virulence to wheat, Triticum aestivum L., was investigated. Clones of greenbug biotypes C, E, and F were induced into the sexual cycle, reciprocally crossed, and inbred. The resulting progeny were cloned via parthenogenetic reproduction, so their virulence to resistance genes Gb2 ('Amigo') and Gb3 ('Largo') could be established using diagnostic feeding lesions. The data for both resistance sources fit a duplicate gene – modifier gene inheritance model where avirulence was dominant and virulence was recessive. Virulence to genes Gb2 and Gb3 was conditioned by duplicate genes and a dominant modifier gene epistatic to one of the duplicate genes. Linkage was definite among the genes conditioning virulence to Gb2 and Gb3 when heterozygous males were used in crosses, as a result of achiasmic spermatogenesis. When homozygous males were used in reciprocal crosses, 50% recombination occurred. This unique linkage affinity suggests that the multiple genes conditioning virulence to Gb2 and Gb3 reside on the same chromosomes but are ≥50 map units apart. Specific aphid–host genetic interactions did not fully conform to the gene-for-gene inheritance hypothesis normally associated with host–parasite relationships. Nevertheless, polygenic inheritance of greenbug virulence in wheat could easily be regarded as a gene-for-gene relationship because the duplicate gene – modifier gene mode of inheritance still influences a single gene product in the aphid.Key words: Schizaphis graminum, Triticum aestivum, insect resistance, insect virulence, insect biotypes.
Effects of inbreeding and estimates of additive genetic variance within seven summer oilseed rape cultivars
Authors: Brandle J. E. , McVetty P. B. E.
Published: April 2011

Seven groups of inbred lines derived from the summer oilseed rape (Brassica napus ssp. oleifera) cultivars 'Westar', 'Regent', 'Lergo', 'Marnoo', 'Ariel', 'Karat', and 'R83-11' were evaluated at three sites over 2 years, for agronomic characters and seed oil and protein concentrations. Estimates of additive genetic variance and heritability were calculated. Comparison of the mean of inbred lines with the mean of their respective source cultivars indicated little, if any, inbreeding depression in all cultivars except 'Ariel'. It was concluded that dominance is not a major factor in the genetic determination of the characters studied. For every trait in every cultivar, individual inbred lines were identified that exceeded or equaled their respective source cultivar means, indicating that neither heterozygosity per se nor genetic heterogeneity is required to maintain maximum performance in summer oilseed rape. Therefore, the oilseed rape cultivars used in this study were considered to be genetically heterogeneous populations, consisting of some number of generally homozygous lines. Significant additive genetic variance was detected for most traits in most cultivars, indicating that superior inbred lines could be extracted from within cultivars.Key words: inbreeding depression, heritability, Brassica napus L.
Interspecific hybridization between Drosophila species group melanogaster sibling species: isozymic patterns and reproductive relationships
Authors: Goulielmos G. N. , Alahiotis S. N.
Published: April 2011

In spite of previous consensus that no F1 fertile hybrids (of both sexes) could be produced between any mating combination of Drosophila melanogaster, D. simulans, and D. mauritiana, the present data indicate that such hybrids were obtained. Thus, some crosses between D. mauritiana females and D. simulans or D. melanogaster males yield F1 fertile hybrids (of both sexes) which have been named Masi (or Masi-2 and Masi-3) and Mame, respectively. Electrophoretic studies, using the species-diagnostic genes for 6-phosphogluconate dehydrogenase, alcohol dehydrogenase, and aldehyde oxidase (6-Pgd, Adh, and Aldox, respectively), were used to investigate the hybrid status, taking into consideration (i) their reproductive relationships, (ii) the coexistence of electromorphs from different species in the same hybrid, within the same generation, and (iii) the expression of the above electromorphs in the hybrids as well as in progeny from backcrosses, where unexpected irregularities and abnormalities were observed. These interspecific hybrids have been kept in our laboratory (as stocks) for 50 generations, to date, and have also been tested for various characteristics that contributed to the verification of their hybrid status (mating abilities, enzyme activities, hybrid sex ratio, the morphology of male genital arches and other fitness components). The finding of major genetic phenomena (e.g., allozymic repression) in these hybrid genomes gives some idea of the nature of events that could be associated with strong evolutionary changes, thus controlling speciation processes.Key words: Drosophila, electrophoresis, electromorphs, interspecific hybrids.
Identification of a heat-shock pseudogene from Caenorhabditis elegans
Authors: Heschl Mark F. P. , Baillie D. L.
Published: April 2011

While characterizing the hsp70 gene family from Caenorhabditis elegans we encountered an unusual member of this family. Sequence data reveal that the hsp-2ps gene is a pseudogene of the constitutively expressed, heat-inducible hsp-1 gene. Two stop codons generated near the 5′ end of the sequence as well as several frameshift mutations and a large internal deletion confirm the identification of hsp-2ps as a pseudogene. The nucleotide substitution rate of the third codon position was twice that of the first and second codon positions, suggesting that the hsp-2ps gene was nonfunctional since the time of the duplication event. The hsp-2ps gene duplicates a region of the hsp-1 gene that lies exclusively within the transcribed region and retains the introns. We feel that the hsp-2ps gene was produced by a transpositional duplication event, which occurred approximately 8.5 million years ago.Key words: heat shock, pseudogene, Caenorhabditis elegans, hsp70.
Chromosomal variation in hybrids between Nicotiana repanda Willd. and N. tabacum L. through pollen and egg-cell irradiation techniques
Authors: Shintaku Y. , Yamamoto K. , Takeda G.
Published: April 2011

Viable interspecific hybrids between Nicotiana repanda Willd. and N. tabacum L. are not possible by conventional hybridization but can be obtained by irradiation treatments of pollen or egg cells combined with in vitro culture of fertilized ovules. In this study cytological analyses were conducted to define chromosomal variation among viable interspecific hybrids obtained by irradiation-mediated techniques. Pollen of N. tabacum was subjected to gamma-ray irradiation dosages of 5–40 kR and used to fertilize N. repanda. Similarly, egg cells of N. repanda were treated with 1–4 kR irradiation and pollinated with N. tabacum. Chromosome number decreases in resulting interspecific hybrids were not as great as had been reported in previous studies, but exposure to higher doses of radiation induced a considerable degree of chromosomal rearrangement. Among resulting hybrids, a number reached the flowering stage. The longevity of the hybrids seemed to be correlated with their ability to generate roots (i.e., rooting vigor). Although the dosage ranges used in the egg-cell irradiation (1–4 kR) were lower than those used in the pollen irradiation (5–20 kR), the degree and quality of the chromosomal variation did not differ.Key words: wide hybridization, hybrid inviability, chromosome variation, tobacco.
Homoeologous pairing and recombination between the long arms of group 1 chromosomes in wheat × rye hybrids
Authors: Naranjo T. , Fernández-Rueda P. , Goicoechea P. G. , Roca A. , Giráldez R.
Published: April 2011

The relationship between homoeologous pairing at metaphase I and recombination at anaphase I between the arms 1AL, 1BL, 1DL, and 1RL was analyzed in ph1b, 5B-deficient, and ph2b wheat × rye hybrids. All four arms could be identified at metaphase I, as well as the arms 1BL and 1RL at anaphase I, by means of C-banding. On the basis of the C-heterochromatin constitution that 1BL and 1RL showed at anaphase I and that association at metaphase I was essentially homoeologous, the following anaphase I chromosome types could be distinguished: parental type, single and double recombinant types between 1BL and 1AL or 1DL, between 1BL and 1RL, and between 1RL and 1AL or 1DL. Recombinant types 1AL – 1DL did not differ from the parental type for the C-banding pattern and was not considered. In the three genotypes, most if not all of 1BL – 1AL, 1BL – 1DL, and 1BL – 1RL metaphase I bonds were chiasmatic. 1RL – 1AL and 1RL – 1DL associations were scarce. Frequencies of one chiasma and two chiasmata for the arm combinations 1BL – 1AL plus 1BL – 1DL, 1BL – 1RL, and 1RL – 1AL plus 1RL – 1DL were estimated. Values decreased in the order ph1b, 5B-deficient, and ph2b hybrids.Key words: C-banding, chiasmata, homoeologues, anaphase I, ph genes.
A new procedure to construct confidence intervals for genotypic variance and expected response to selection
Authors: Tai G. C. C.
Published: April 2011

This paper describes a procedure to construct confidence intervals for genotypic variance and expected response to selection estimated from progeny test experiments. It involves the introduction of parameters into the confidence limits of existing exact confidence intervals for variance and variance ratio. The parameters in the limits of the derived intervals are estimated by comparing the limits of different potential intervals covering the same parameter, i.e., genotypic variance or expected response to selection. This leads to the construction of a confidence interval for the concerned parameter.Key words: confidence intervals, genotypic variance, expected response to selection.
Supernumerary chromosome evolution in the Simulium vernum group (Diptera: Simuliidae)
Authors: Brockhouse Charles , Bass J. A. B. , Feraday R. M. , Straus N. A.
Published: April 2011

B chromosomes are present in a cluster of closely related species of black fly in the Simulium vernum group including six sibling species within the S. vernum complex, Simulium costatum, and Simulium juxtacrenobium. The S. vernum siblings all possess the same small metacentric supernumerary, while S. juxtacrenobium carries three different supernumeraries (two telocentrics and one metacentric) and S. costatum has both a metacentric and a telocentric B chromosome. Analysis of the polytene chromosomes in the larval salivary glands has revealed relationships between the supernumeraries of the different species. The metacentric B chromosome of the S. vernum siblings apparently results from a fusion of the two telocentric supernumeraries of S. juxtacrenobium. Acquisition of a nucleolar organizer then gave rise to the metacentric B chromosome in S. juxtacrenobium. The acquisition of a nucleolus by a S. juxtacrenobium telocentric gave rise to one of the S. costatum supernumeraries. Two alternate models for the origin of black fly supernumeraries are presented.Key words: supernumerary chromosome, black fly, polytene chromosome, chromosome evolution.
The polytene chromosomes of Simulium furculatum (Shewell) (Diptera: Simuliidae)
Authors: Hunter Fiona F.
Published: April 2011

To test whether Simulium furculatum (Shewell) belongs to the Simulium vernum (Macquart) species-group, a comparison was made of the polytene chromosomes of S. furculatum and the S. vernum "Knebworth" standard. Only two chromosome arms (of six) could be completely analysed. It is argued that S. furculatum does not belong to the S. vernum species-group. A complex sex-chromosome system (X1, X2, Y1) is found in both eastern and western Canada. Phylogenetically, the single Y chromosome is intermediate between the two X chromosomes. Intraspecific inversion polymorphisms, which serve to differentiate eastern from western populations, are also identified. Only one sibling is indicated.Key words: black flies, Simulium furculatum, Simulium vernum, cytotaxonomy, polytene chromosomes, sex chromosomes.
A cytological description of Eusimulium vernum, E. decolletum, and the E. pugetense complex (Diptera: Simuliidae) in Alaska
Authors: Allison Lizabeth A. , Shields Gerald F.
Published: April 2011

Larval populations of the black flies Eusimulium vernum, E. decolletum, and E. pugetense in Alaska were analyzed using polytene chromosome cytology. One cytotype ("Knebworth") of E. vernum was found and cytotypes A and B of E. pugetense were found, with cytotype B having distinct northern and southern variants. No fixed inversions were found between E. decolletum and E. vernum, an interpretation that differs from a previous publication. Eusimulium decolletum is characterized cytologically by its profile of polymorphisms, the lack of B chromosomes, and partial sex linkage of IIIL-1de. Detailed collection information is also presented for E. vernum, E. decolletum, and E. pugetense.Key words: black flies, cytogenetics, chromosomal inversions, evolution.
Fluorescence banding in mitotic and meiotic chromosomes of the Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae)
Authors: Bedo D. G.
Published: April 2011

Mitotic and meiotic chromosomes of the Mediterranean fruit fly, Ceratitis capitata, were studied using three counterstain-enhanced fluorescence staining methods. The tristaining technique allowed chromomycin A3 (CMA) and distamycin – diamidinophenylindole (DA–DAPI) fluorescence to be observed on the same chromosomes. DAPI–actinomycin D (DAPI–AMD) fluorescence was also carried out. These techniques were complemented with quinacrine staining and C-banding. The results were compared with earlier data on silver staining. The sex chromosomes, particularly the X chromosome, show great banding detail with extensive longitudinal differentiation in mitotic chromosomes. GC- and AT-specific fluorescence is not found in the expected reciprocal pattern at all sites. Comparison with C-banding and silver staining shows that intense fluorescence occurs in lightly C banded regions and silver bands correspond to fluorescent bands rather than nucleolar organizers. The combination of staining data suggests that much of the X chromosome has characteristics intermediate between heterochromatin and euchromatin. Meiotic X chromosomes show much less detail and reduced fluorescence intensity but can still be easily traced throughout meiosis and spermatogenesis.Key words: fluorescence banding, sex chromosomes, Mediterranean fruit fly, Ceratitis capitata.
Chromosome core attachment to the meiotic nuclear envelope regulates synapsis in Chloealtis (Orthoptera)
Authors: Moens Peter B. , Bernelot-Moens Cecilia , Spyropoulos Barbara
Published: April 2011

Genetic evidence shows that in inbred families of Chloealtis conspersa, exceptional synapsis occurs between the distal ends of chromosomes 7 and 8 only if the other chromosome 7 carries a supernumerary (B) segment at its distal end. Cytological evidence shows that all the ends of chromosome cores are attached to the nuclear envelope and that synapsis is initiated close to the nuclear envelope. It is shown that distal synapsis of homologues 7 and 7B is perturbed by the B segment, which causes a misalignment of normally homologous regions at the nuclear envelope. It is proposed that this misalignment permits ends of heterologous chromosomes to undergo synapsis if they have mutual distal homologies (common in grasshoppers). In this manner the association between chromosome core ends and nuclear envelope regulates synapsis and chiasma formation in Chloealtis. Other organisms have different heterochromatic polymorphisms and pairing modes, but chiasma redistribution may result from a similar mechanism.Key words: Orthoptera, synaptonemal complex, synapsis regulation, heterologous synapsis, meiosis, nuclear envelope, heterochromatin.
Ultrastructure of meiotic pairing in B chromosomes of Crepis capillaris. I. One-B and two-B pollen mother cells
Authors: Jones G. H. , Whitehorn J. A. F. , Albini S. M.
Published: April 2011

Chromosome pairing of a small metacentric B chromosome in Crepis capillaris has been studied by synaptonemal complex surface spreading of pollen mother cells containing either one or two B chromosomes. The B-chromosome axis, on average, represents about 8.7% of the axis length of the standard A-chromosome set, which is less than the corresponding values for DNA content (10.6%) and mitotic chromosome volume (13.6%). Single B chromosomes commonly undergo fold-back pairing to give a symmetrical hairpin loop, which supports earlier suggestions that this B chromosome is an isochromosome. Two B chromosomes may show interarm pairing, exclusively, or interchromosome pairing, exclusively, or combinations of the two. Near the centromeres pairing occurs preferentially between arms of the same chromosome, but chromosome ends show random association. Some B chromosomes show anomalous pairing configurations, which may reflect further orders of reverse repeats within arms or, alternatively, nonhomologous pairing. The period of B-chromosome pairing is confined almost exclusively to zygotene, when the standard A chromosomes are pairing, but within this period their pairing is delayed relative to the A set. Individual B chromosomes at zygotene contain from one to three separate synaptonemal complex segments. These are widely distributed within the chromosomes, mainly in distal and interstitial regions; pairing is delayed around the centromere.Key words: B chromosomes, isochromosomes, synaptonemal complex.
Cloning and characterization of a tandemly repeated DNA sequence in the crane family (Gruidae)
Authors: Chen Z.-Q. , Lin C. C. , Hodgetts R. B.
Published: April 2011

A tandemly repeated DNA sequence possessing a unique PstI site has been characterized in several species of the crane family. The "Pst family" comprises at least 8800 monomer units 187 base pairs (bp) in length and constitutes 0.14% of the genome of the sarus crane (Grus antigone). The array is located in the centromeric heterochromatin of chromosome 2 in the two species where in situ hybridizations of a cloned monomer to metaphase chromosome spreads were carried out. DNA sequence comparisons between five monomer units from G. antigone revealed a high degree of homology between four of the individual repeats, while the fifth was somewhat divergent. The G+C content deduced from the DNA sequence makes it likely that the Pst family constitutes part of a density satellite seen in profiles of crane DNA centrifuged to equilibrium in CsCl. The common occurrence of tandem arrays such as the Pst family, with repeat lengths close to 200 bp, leads us to an hypothesis implicating nucleosomes in the evolution of such families.Key words: repeated gene families, satellite DNA, centromeric heterochromatin, taxonomy of Gruidae.
Heat-shock response in a tropical Chironomus: seasonal variation in response and the effect of developmental stage and tissue type on heat shock protein synthesis
Authors: Nath B. B. , Lakhotia S. C.
Published: April 2011

Examination of heat shock induced transcriptional activity in salivary gland polytene nuclei of a tropical Chironomus, C. striatipennis, revealed nine heat-shock puffs. In 24 °C-reared larvae optimal heat-shock response was seen at 39 °C, while a 41 °C shock was nearly lethal. In a population grown under natural conditions of seasonal variations, the heat-shock response was dependent upon the current ambient temperature. In summer months, response to 39 °C was variable, from complete to no induction of heat-shock puffs in different cells. In control glands from larvae growing at 33–36 °C in summer, heat-shock genes were not active, although in 24 °C-reared larvae, 33 °C already caused partial induction. Unlike the 24 °C-reared population, a 41 °C shock to summer larvae was not lethal. [35S]Methionine-labelled protein synthesis pattern in the summer larvae revealed appreciable accumulation of heat-shock polypeptides in control glands, which possibly autoregulates their further induction and also explains the better thermotolerance of these larvae. In a developmental study of a 24 °C-reared population, some heat-shock polypeptides were found to be commonly synthesized at 39 °C in all the tissues (salivary glands of larvae; Malpighian tubules of larvae, pupae, and adult; adult ovaries), while other heat-shock polypeptides showed apparent tissue and (or) developmental stage specificity. Heat shock protein 70 was most abundantly synthesized in all the tissues examined.Key words: temperature shock, thermotolerance, heat-shock polypeptides, polytene chromosomes, puffs.
DNA restriction fragment length polymorphisms: a strategy for genetic mapping of D genome of wheat
Authors: Kam-Morgan L. N. W. , Gill B. S. , Muthukrishnan S.
Published: April 2011

The use of restriction fragment length polymorphisms (RFLPs) as genetic markers in bread wheat, Triticum aestivum, and a wild wheat progenitor, Aegilops squarrosa, was investigated. The objectives were (i) to identify RFLP loci; (ii) to assign cDNA sequences onto specific chromosomes and chromosome arms; and (iii) to determine linkage relationships between RFLP loci. A low level of polymorphism was found, utilizing barley cDNA clones as probes, in hexaploid cultivated wheats. However, accessions of A. squarrosa revealed greater polymorphism. Wheat–barley alien addition lines were used to assign 17 cDNA sequences to specific chromosome groups and ditelosomic and nullisomic–tetrasomic wheat stocks were used to assign these sequences to specific chromosome arms. Of 16 sets of RFLP loci, excluding α-Amy-1 and α-Amy-2, 14 are new sets of loci marking 6 of the 7 homoeologous groups of wheat. The construction of a linkage map of chromosome 5D was initiated by analyzing a segregating F2 population between two homozygous accessions of A. squarrosa. A strategy using wheat aneuploids for chromosome arm location and a segregating A. squarrosa population for linkage measurement was demonstrated for mapping the D-genome chromosomes of wheat.Key words: genetic map, restriction fragment length polymorphisms, Triticum aestivum, Aegilops squarrosa, polyploidy.