bluuebunny/crossref_metadata_2025 huggingface dataset:
Orientation of diplochromosomes in mitoses of potato (Solatium tuberosum L.) callus cultures
Authors: Pijnacker L. P. , Ferwerda M. A.
Published: April 2011

The mitotic behaviour of diplochromosomes was investigated in early calli from leaf segments of a monohaploid potato (x = 12) with the aid of the fluorescent plus Giemsa technique. The sister chromosomes of the diplochromosomes do not separate during metaphase because the inner chromatids remain connected. Consequently the diplochromosomes orient in three stable configurations during metaphase. In the case in which sister chromosomes become auto-oriented, the outer chromatids face one pole and the inner chromatids the opposite pole (U-shaped configuration), or the outer and inner chromatid of each sister chromosome face different poles (alternate configuration). Less frequently the sister chromosomes become oriented to different poles (C-shaped configuration). Linear orientation is not observed. At least until the onset of telophase only the inner chromatids originating from U-shaped configurations may remain paired, but they fall apart before the next metaphase. The mitoses with diplochromosomes give rise to two cells with double the number of chromosomes.Key words: potato, diplochromosomes, mitosis, orientation, polyploidization.
Evolutionary implications of duplications and Balbiani rings in Drosophila. A study of Drosophila serrata
Authors: Mavragani-Tsipidou P. , Kyrpides N. , Scouras Z. G.
Published: April 2011

Drosophila serrata, a species of subgroup montium, exhibits in its salivary-gland chromosomes a high number of inverted tandem duplications and a well-formed Balbiani ring. A photographic map, the duplications, and the Balbiani ring of this species are presented. Also presented are the most prominent puffs during normal larval development and after ecdysone treatment, as well as intercalary heterochromatin regions of the above chromosomes. These data are discussed and compared with those of Drosophila auraria, another species of subgroup montium. All the inverted tandem duplications found in both species are homozygous and are not accompanied by other types of chromosomal rearrangements. These results argue in favor of the relatively old origin of these structures. The similarity of the structure and the developmental profile of the Balbiani ring 1 in both species may indicate a necessary role served by the Balbiani ring 1 and hence its selection during evolution.Key words: Drosophila, duplications, Balbiani ring, ecdysone, intercalary heterochromatin.
Karyotyping Melandrium album, a dioecious plant with heteromorphic sex chromosomes
Authors: Ciupercescu D. D. , Veuskens J. , Mouras A. , Ye D. , Briquet M. , Negrutiu I.
Published: April 2011

Mitotic metaphase chromosomes of Melandrium album obtained from root protoplasts were studied. Morphologically, the chromosomes were either metacentrics or submetacentrics. They were classified into three distinct groups: group A comprising six pairs of autosomal metacentrics, group B comprising five pairs of autosomal submetacentrics, and the sex chromosomes: X and Y. The X chromosome is a metacentric (r = 1.44), which accounts for more than 14% of the genome. The Y chromosome is a metacentric with, virtually, equal arms (r = 1.09) and accounts for 21% of the genome, being the largest of the complement. The Y:X ratio was 1.4. Ethidium bromide, caffeine, and vinblastine were used to obtain a better resolution and higher frequency of satellited chromosomes 7q and 9p. The proposed karyotype of M. album is 2n = 24, XX, s(7q;9p) for female and 2n = 24, XY, s(7q;9p) for male plants. Nucleolus organizer regions (NORs) were present at the telomeric sites of three chromosome pairs: 7q, 9p, and 10p. The NORs were polymorphic, particularly between the nonhomologous chromosomes. The in situ hybridization technique localized the rRNA genes on four chromosome pairs: 5p, 7q, 9p, and 10p. The discrepancy between the NORs and the hybridization signals was probably due to the fact that NORs were restricted only to transcriptionally active rRNA genes. It was concluded that for a complete description and characterization of rRNA genes, both NOR detection and in situ hybridization techniques, as complementary methods, should be employed.Key words: Melandrium album, karyotype, satellites, idiogram, nucleolus organizer regions, in situ hybridization.
Nature of chromosome pairing in SH-genome octaploids involving Elymus canadensis and E. trachycaulus: a genome dose dependent bivalentizing mechanism
Authors: Kumar P. S. , Walton P. D.
Published: April 2011

In spite of regular chromosome pairing, hybrids between Elymus canadensis (Linnaeus) and E. trachycaulus (Link) Gould ex Shinners at the tetraploid level are sterile owing to structural differences between the donor genomes. However, the hybrids between these species at the octaploid level (obtained through chromosome doubling of the tetraploid hybrid and also from a cross between the octaploids of E. canadensis and E. trachycaulus) exhibited a predominance of bivalents in meiosis in spite of the autotetraploid nature of their constituent S and H genomes. The colchicine-induced amphiploids showed varying degrees of fertility. Comparison of chromosome pairing in the hybrid octaploids with that in the parental octaploids and hexaploids revealed that random bivalent formation is promoted when the S and (or) H genomes are at the tetraploid level, but not when they are in the triploid state. A bivalentizing mechanism under polygenic control is suggested to explain the predominance of bivalents in the tetraploid S and H genomes.Key words: Elymus, S genome, H genome, octaploids, bivalents, bivalentization.
Interchange chromosomes in Simulium nigricoxum Stone Diptera: Simuliidae
Authors: Shields Gerald F.
Published: April 2011

A whole-arm interchange (IS-IIIL/IL-IIIS) is described from a larval population of Simulium nigricoxum Stone in the Yukon Territory. Although unstudied elsewhere, S. nigricoxum appears to differ from its closest presumed relative, Simulium malyschevi, by the whole-arm interchange, a fixed autosomal inversion in the short arm of the second chromosome, and a sex-linked inversion also in the short arm of the second chromosome. It is possible that the interchange provided a chromosomal basis for reproductive isolation of S. nigricoxum from an ancestral form, but because of its apparent localized distribution that hypothesis must remain tentative.Key words: Simulium nigricoxum, Simulium malyschevi, chromosome interchanges, inversions, reproductive isolation.
Use of interplasmid recombination to generate stable selectable markers for yeast transformation: application to studies of actin gene control
Authors: Hubberstey Andrew V. , Wildeman Alan G.
Published: April 2011

A plasmid recombination system has been developed that relies upon interplasmid exchanges for yeast cell viability. Two types of plasmids, one carrying the LEU2 allele inserted within yeast actin gene sequences and the other carrying 2-μm plasmid DNA and an intact actin gene, were constructed. Neither plasmid alone yielded transformants in the haploid Leu− strain AH22, but when cotransformed, a number of colonies were obtained. Southern blot analysis revealed that transformants arose because of recombination events within the homologous actin sequences that transferred the LEU2 gene to the actin gene on the 2-μm plasmid. The recombinant plasmids could be recovered, and sequence analysis of one recombination site revealed that the exchange event was faithful at the nucleotide level. The resulting recombinant plasmids carried a defective actin gene and presumably arose because of a double-crossover event. Deletion mutations that prevented actin gene expression on one donor plasmid enabled the recovery at a high frequency of transformants resulting primarily from single-crossover events between the two plasmids. This was presumably because such events no longer generated an intact actin gene on a multicopy plasmid. Infrequently a transformant from a plasmid with an intact gene was recovered, but in these cases the plasmid was not present in multiple copies. These cells exhibited a slower growth rate, and Northern blot analysis revealed an elevated level of actin mRNA.Key words: homologous recombination, regulation, gene disruption, tranformation, actin.
Evolutionarily conserved regions in Caenorhabditis transposable elements deduced by sequence comparison
Authors: Prasad Shiv S. , Harris Linda J. , Baillie David L. , Rose Ann M.
Published: April 2011

In this paper we present the sequence of an intact Caenorhabditis briggsae transposable element, Tcb2. Tcb2 is 1606 base pairs in length and contains 80 base pair imperfect terminal repeats and a single open reading frame. We have identified blocks of T-rich repeats in the regions 150–200 and 1421–1476 of this element which are conserved in the Caenorhabditis elegans element Tc1. The sequence conservation of these regions in elements from different Caenorhabditis species suggests that they are of functional importance. A single open reading frame corresponding to the major open reading frame of Tc1 is conserved among Tc1, Tcb1, and Tcb2. Comparison of the first 550 nucleotides of the sequence among the three elements has allowed the evaluation of a model proposing an extension of the major open reading frame. Our data support the suggestion that Tc1 is capable of producing a 335 amino acid protein. A comparison of the sequence coding for the amino and carboxy termini of the 273 amino acid transposase from Caenorhabditis Tc1-like elements and Drosophila HB1 showed different amounts of divergence for each of these regions, indicating that the two functional domains have undergone different amounts of selection. Our data are not compatible with the proposal that Tc1-related sequences have been acquired via horizontal transmission. The divergence of Tc1 from the two C. briggsae elements, Tcb1 and Tcb2, indicated that all three elements have been diverging from each other for approximately the same amount of time as the genomes of the two species.Key words: Caenorhabditis, transposable element, sequence comparison.
Distributive pairing in the grasshopper Chorthippus binotatus
Authors: Lopez-Leon M. D. , Cabrero J. , Camacho J. P. M.
Published: April 2011

Six males of the grasshopper Chorthippus binotatus were mosaic for the presence of extra (E) chromosomes in the germ line, but lacked them in the somatic cells of gastric caeca. E chromosomes were very similar to the X chromosome in size and meiotic properties (heteropycnosis and autopairing). X and E chromosomes associated frequently at diplotene, but the associations never persisted until metaphase I, which indicated that they were not chiasmate. When one E was present, X and E univalents segregated preferentially to opposite poles. In cells with two E, they formed a bivalent in almost all cells, and decreased the frequency of X–E associations by 20%. These cells showed a high frequency of nondisjunction between the two E chromosomes, such that they segregated independently despite the high persistence of their association at metaphase I. These results are interpreted and discussed in the light of the distributive pairing model.Key words: distributive pairing, X chromosome, E chromosome, Chorthippus, male meiosis.
Differential response to chilling injury of the group 6 chromosomes of cv. Chinese Spring wheat
Authors: Whelan Ernest D. P.
Published: April 2011

Winter wheat (Triticum aestivum L.) requires vernalization (exposure to temperatures between 1 and 10 °C) to induce heading. Vernalization also induces earlier heading of many spring wheat varieties. Studies of the spring wheat cv. Chinese Spring identified cytogenetic lines of the group 6 chromosomes that were susceptible to chilling injury when seedlings were grown at 6 °C for 8 weeks. Lines that were either ditelocentric for the long arm of chromosome 6D or nullisomic for 6D were susceptible, while those ditelocentric for the short arm of 6D were not. Neither cv. Chinese Spring nor ditelocentrics for either the long or short arms of chromosomes 6A or 6B were susceptible. Susceptible plants selected from F2 seedlings of plants monosomic for 6D were nullisomics. Doublemonotelocentric F1 hybrids from crosses between plants ditelocentric for 6DS or 6DL were resistant, but susceptible F2 seedlings from this cross were either nullisomic for 6D or telocentric for the long arm. The dominant gene(s) that prevents chilling injury at 6 °C appears to be on the short arm of chromosome 6D of cv. Chinese Spring wheat.Key words: chilling injury, wheat, telocentrics, nullisomics, vernalization.
Cytogenetics of fertility improvement in artificial autotetraploids of Hyoscyamus niger L.
Authors: Lavania U. C. , Srivastava Sangeeta , Sybenga J.
Published: April 2011

Genetically stable artificial autotetraploids with over 90% seed set were obtained by colchicine treatment of the solanaceous species Hyoscyamus niger L. (4x = 68). The tetraploids were vigorous and had earlier been shown to yield considerably more tropane alkaloid per individual than the source diploids. The tetraploids had high bivalent frequencies at meiosis, and high fertility as a result of the formation of genetically balanced gametes. There was a systematic and significant decrease in quadrivalent frequency and an increase in bivalent frequency in three subsequent generations tested (C0, C1, C2). Possible causes of high bivalent frequency are discussed. Seed fertility can probably be increased in advanced generations by further selection for fertility and maximization of heterozygosity.Key words: Hyoscyamus niger, autotetraploid, meiosis, bivalents, fertility, selection.
A cytogenetic analysis of the polytene chromosomes of Anopheles triannulatus (Diptera: Culicidae) from western Venezuela
Authors: Conn Jan
Published: April 2011

The larval polytene chromosomes of Anopheles triannulatus are described for the first time in this report. The population from western Venezuela was chosen arbitrarily as the chromosome standard and is the basis for the photomap presented here. Anopheles triannulatus displays whole-arm associations distinct from other members of the subgenus Nyssorhynchus that have been examined cytogenetically. The association pattern for An. triannulatus is 2R–3R and 2L–3L, rather than the more common 2R–2L and 3R–3L. The possible role of whole-arm translocations in speciation is briefly discussed.Key words: Anopheles triannulatus, polytene chromosome photomap, whole-arm translocation, Venezuela.
Transient expression of marker genes in immature zygotic embryos of spring wheat (Triticum aestivum) through microprojectile bombardment
Authors: Chibbar R. N. , Kartha K. K. , Leung N. , Qureshi J. , Caswell K.
Published: April 2011

Transient expression of marker genes (cat and uidA) delivered by the Biolistics microprojectile bombardment technique has been detected in immature zygotic embryos of wheat (Triticum aestivum L.). The DNA expression vectors that gave maximal expression of both cat (pCaMVI1CN) and uidA (pCaMVI1GusN) genes had an alcohol dehydrogenase (Adh1) intron 1 cloned in between the cauliflower mosaic virus (CaMV35S) promoter and the coding region of the gene. Detection of chloramphenicol acetyltransferase (CAT) activity in response to cat gene was complicated by the presence of an inhibitor of CAT activity as well as an endogenous CAT-Iike activity. The results of enzymatic assays were confirmed by an ELISA technique using CAT-specific antibodies, whereas the β-glucuronidase (GUS) activity following the introduction of the uidA gene was confirmed by both histochemical and fluorometric techniques.Key words: cereal transformation, gene expression, ELISA, wheat.
A rapid technique for the detection of wheat–rye translocation chromosomes
Authors: May Cedric E. , Wray Fiona
Published: April 2011

After 1–2 days on nitrocellulose filters kept moist with Tris–NaCl–EDTA (TNE) solution, sufficient DNA is adsorbed from individual half seeds of wheat to allow rye heterochromatin sequences to be detected in the adsorbed samples. Using the probe pSchet1, seeds of rye (Secale cereale), triticale (× Triticosecale), wheat (Triticum aestivum), and wheat containing 1RS/1BL translocation chromosomes have been successfully screened for the presence or absence of this heterochromatin sequence. The system has the potential to recognise the presence of the short arm of chromosome 1R of rye, and the presence of other rye DNA sequences, in thousands of samples per week.Key words: wheat, 1RS/1BL translocation, rye, heterochromatin, pSchet1
The chromomere map of the pachytene spermatocyte of the Turkish hamster (Mesocricetus brandti)
Authors: Fang Jye-Siung , Jagiello Georgiana M.
Published: April 2011

The chromomere map of the early to mid pachytene spermatocyte of the Turkish hamster (Mesocricetus brandti) is described. Each autosomal bivalent was identified and a total of 304 chromomeres was found. A sex bivalent with a despiralized Xq protruding from the sex vesicle and a small number of the polymorphic 16q bivalents were observed.Key words: Turkish hamster, chromomere maps, pachytene spermatocytes.
Sequence and structure of mtr, an amino acid transport gene of Neurospora crassa
Authors: Koo Kenneth , Stuart W. Dorsey
Published: April 2011

The gene product of the mtr locus of Neurospora crassa is required for the transport of neutral aliphatic and aromatic amino acids via the N system. We have previously cloned three cosmids containing Neurospora DNA that complement the mtr-6(r) mutant allele. The cloned DNAs were tightly linked to restriction fragment length polymorphisms that flank the mtr locus. A 2.9-kbp fragment from one cosmid was subcloned and found to complement the mtr-6(r) allele. Here we report the sequence of the fragment that hybridized to a poly(A)+ mRNA transcript of about 2300 nucleotides. We have identified an 845-bp open reading frame (ORF) having a 59-bp intron as the potential mtr ORF. S1 nuclease analysis of the transcript confirmed the transcript size and the presence of the intron. A second open reading frame was found upstream in the same reading frame as the mtr ORF and appears to be present in the mRNA transcript. The mtr ORF is predicted to encode a 261 amino acid polypeptide with a molecular mass of 28 613 Da. The proposed polypeptide exhibits six potential α-helical transmembrane domains with an average length of 23 amino acids, does not have a signal sequence, and contains amino acid sequence homologous to an RNA binding motif.Key words: sequence, membranes, ribonucleoprotein.
Linkage relationships of allozyme-encoding loci in shiitake, Lentinula edodes
Authors: Bowden Christine G. , Royse Daniel J. , May Bernie
Published: April 2011

Single spore derived isolates from two parental and seven hybrid lines of Lentinula edodes were analyzed for single locus and joint segregation of 21 allozyme-encoding loci. The two alleles at the individual loci departed significantly from a 1:1 Mendelian ratio in 11% of the tests. With the exception of the highly significant χ2 value for Aat-1 in line WC131 (χ2 = 41.78), aberrant ratios were marginally significant and probably were due to chance alone. Eight linkages were identified: Ada ~ Gda, recombination frequency (r) = 0.15; Ada ~ Est, r = 0.12; Est ~ Gpi, r = 0.29; Ada ~ Gpi, r = 0.35; Gdh ~ Sod-1, r = 0.18; Mpi ~ PepG1-2, r = 0.13; Mpi ~ Sod-2, r = 0.04; and Sod-2 ~ PepG1-2, r = 0.14. Twelve loci were not shown to be linked to any other loci (Aat-1, Ak, Cat, Dia, Gk, β-Glu-1, β -Glu-2, Mdh, PepLgg-2, Pgd, Pgm, and Np). The first linkage map of 10 allozyme-encoding loci for the L. edodes genome is presented.Key words: shiitake, Lentinula edodes, allozymes, linkage map, edible fungi.
Chromosomal divergence and heterogameity in two annual killifishes of the genus Pterolebias
Authors: Elder Jr. John F. , Turner Bruce J. , Thomerson Jamie E. , Taphorn Donald C.
Published: April 2011

The annual killifish (Cyprinodontidae) species Pterolebias hoignei and Pterolebias zonatus from the Orinoco basin, Venezuela, have been regarded as conspecific ecomorphs, but P. hoignei has a diploid number of 46, whereas P. zonatus has a diploid number of 42. Metacentric chromosome counts also differ between these two species. Pterolebias hoignei has a sexually dimorphic karyotype, while P. zonatus does not. Although the diploid number is the same for both sexes, male P. hoignei possess a single large Y chromosome not present in the female karyotype. The hypothesis of conspecificity is rejected on the basis of karyotypic divergence found between the species.Key words: Cyprinodontidae, karyotype divergence, sexual dimorphism.
Genetic and cytogenetic maps of chromosomes 1R, 4R, and 7R in cultivated rye (Secale cereale)
Authors: Figueiras Ana M. , Elorrieta María A. , Benito César
Published: April 2011

To obtain genetic and cytogenetic maps in rye, two different interchanges, both between 4R and 5R chromosomes, have been studied. In each case, several separate testcrosses for structural and isozyme heterozygous plants and their progeny were analyzed. Linkage was found between the isozyme loci Pgi-1 and Mdh-4 (35.38 centimorgans (cM)), Mdh-4 and Mdh-1 (5.21 cM), Pgi-1 and Mdh-1 (32.37 cM), Mdh-4 and Pgd-2 (28.00 cM), L1Per-1 and Alph-1 (21.43 cM), Alph-2 and Alph-5 (34.37 cM), Alph-2 and Acph (12.24 cM), and Alk-3 and Acph (19.12 cM). Regarding the chromosomes involved in the two translocations, the results obtained in this work are in agreement with previous C-banding data. Thus, the Pgm-1 locus, located in the 4RS chromosome arm, is linked to both translocations. The estimated distance between this locus and the centromere is 14.63 cM in the 4RL/5RS interchange and 16.82 cM in the 4RL/5RL interchange.Key words: translocations, isozymes, rye, genetic and cytogenetic maps.
A survey of restriction fragment length polymorphisms in tall fescue and its relatives
Authors: Xu W. W. , Sleper David A. , Hoisington David A.
Published: April 2011

Restriction fragment length polymorphisms (RFLPs) have several advantages over conventional genetic markers and as a result have received increased attention from plant breeders and geneticists. The objective of this study was to construct a tall fescue (Festuca arundinacea Schreb.) genomic library and to survey RFLPs in tall fescue and its relatives. Using plasmid pUC19 as a vector and Escherichia coli XL1-Blue cells as hosts, the first reported PstI genomic DNA library has been established from hexaploid (2n = 6x = 42) tall fescue. The genomic clones were evaluated using nine genotypes from three species of Festuca and three restriction enzymes (BamHI, EcoRI, and HindIII). One hundred and seventy-four probes gave readable results, of which 21% were repetitive and 79% single-copy. The single-copy probes revealed good polymorphism in tall fescue. Approximately 21% of the probes did not cross hybridize to any of the diploids or tetraploids or both and, therefore, represented genome-specific clones.Key words: tall fescue, genome-specific probes, genomic library, polyploids, genomic relationships
Genetic stability of the D1Z2 region: implications for DNA genotyping and paternity testing
Authors: Tynan Katherine M. , Parslow Malcolm I. , Hoar David I.
Published: April 2011

The aim of the present study was to examine a single locus variable number tandem repeat for the purpose of DNA genotyping ("fingerprinting"). DNAs of 175 individuals from five ethnic groups (Black, Chinese, Japanese, Caucasian, and Melanesian) were analyzed. Restriction fragment length polymorphic analysis of random individuals revealed individual specific DNA patterns in all but one group. Among 20 Melanesian inhabitants of the Vanuatu islands in the southwest Pacific, three individuals were found to share a common pattern. This island population represents a "genetic isolate" and illustrates the importance of carrying out population studies on individual ethnic groups of interest. The complexity and the genetic stability of the D1Z2 region as revealed by the probe hMF1 make it an excellent candidate for DNA genotyping in paternity testing as 101 Caucasian individuals each had unique patterns for PstI and SinI digests.Key words: DNA fingerprinting, variable number tandem repeat, paternity testing, DNA genotyping.
Cytogenetic analysis of a human familial 15p+ marker chromosome
Authors: Velázquez M. , Visedo G. , Ludeña P. , Cabo S. F. de , Sentís C. , Fernández-Piqueras J.
Published: April 2011

An extreme variant of a human 15p+ marker chromosome is described in a human family. The short arm of this variant is greatly enriched in ribosomal RNA genes, and there are up to three secondary constrictions potentially active for rRNA transcription. These sites are hypomethylated, whereas the rest of rDNA is highly methylated, as shown by the isoschizomer pair HpaII–MspI. This chromosome variant is similar to others previously described for chromosomes 14 and 22, but some differences have been found after C-banding and after treatments with AluI and Sau3AI.Key words: human cytogenetics, 15p+ marker chromosome.
Presence of a centromeric filament during meiosis
Authors: Solari Alberto J. , Tandler Carlos J.
Published: April 2011

Spermatocytes at meiotic metaphase I and anaphase I have a characteristic centromeric filament in a variety of vertebrate organisms. This centromeric filament was first demonstrated on mouse spermatocytes and its presence is now extended to spermatocytes from the human, rat, golden hamster, bull, and chicken. The visualization of this filament was possible through the use of a novel silver-staining technique, which allows a high contrast between the filament and the centromeric chromatin. In the species cited, the centromeric filament shares an intense staining, a short (0.2–0.6 μm) length, a curved and branched shape, and location inside the centromeric chromatin of seemingly every homologue of the complement. The similarity of staining reactivity and the observation of transitional structures during first meiotic prophase strongly suggest that the centromeric filament is a remnant of a lateral element of the synaptonemal complex, which stays specifically at both centromeric regions of each bivalent. This filament is not found at the second meiotic division or at the centromeres of mitotic chromosomes. It is assumed that this centromeric filament joins the two sister chromatids of each homologue at the centromere and thus ensures the proper coorientation of sister kinetochores at metaphase I. Further testable assumptions on the functions of this filament are presented.Key words: synaptonemal complex, meiosis, meiotic centromeres.
Staining plant cells with silver. II. Chromosome cores
Authors: Stack Stephen M.
Published: April 2011

A new technique called salt-nylon silver staining has been used to stain cores in the chromosomes of Lilium longiflorum. Cores are visible in both mitotic and meiotic chromosomes. In C-metaphase chromosomes, a thin core is coiled to form a thick core in each chromatid. In early prophase I of meiosis, silver-stained axial cores and synaptonemal complexes show no indication of coiling before their disappearance in early diplotene. In diakinesis, pairs of thin cores reappear in large major coils. These cores can be seen to cross over between homologous chromosomes. By metaphase I, thin cores coil to form thick cores, which themselves spiral in major coils. The most striking appearance of the cores occurs during anaphase I, when homologous chromosomes separate and sister chromatids swing apart to display thick cores in major coils. During meiosis II cores are in minor coils embedded in elongate chromosomes that show relic major coiling. These observations indicate that plant chromosomes have silver-stainable cores that are comparable with cores that have been reported in the chromosomes of mammals and grasshoppers.Key words: chromosome cores, silver staining, mitosis, meiosis, plants.
Genetic stability of microspore-derived doubled haploids of barley: a cytological, biochemical, and molecular study
Authors: Finnie S. J. , Forster B. P. , Chalmers K. J. , Dyer A. F. , Waugh R. , Powell W.
Published: April 2011

Populations of doubled haploids were produced by culturing microspores from spring barley cv. Tweed, cv. Tyne, and cv. Natasha, on media containing either sucrose or maltose as the only carbohydrate. The populations were analysed for evidence of genetic instability at the karyotype, protein, and DNA levels. The results show very little evidence of induced genetic change. The level of instability is insignificant when compared with that which is observed following meiotic recombination. The stability of microspore-derived lines may be attributed to the embryogenic mode of regeneration, which occurs at a high frequency on a maltose-containing medium. The results are discussed in relation to the exploitation of doubled haploids in barley breeding.Key words: barley, microspore, doubled haploid, stability, karyotype, isozymes, restriction fragment length polymorphism.
Stem-rust resistance in 'Canthatch' hexaploid wheat induced by a nonsuppressor mutation on chromosome 7DL
Authors: Kerber E. R.
Published: April 2011

A recessive null mutation induced in the common wheat cultivar 'Canthatch' by ethyl methanesulphonate permits the expression of resistance to several cultures of stem rust to which this cultivar is susceptible. This susceptibility is due to a dominant suppressor on chromosome 7DL that inhibits resistance conferred by a gene or genes located elsewhere on the genomic complement. Genetical and cytogenetical evidence indicated that the mutation is simply transmitted and was induced either at the suppressor locus or at a locus closely linked with it, more than 50 crossover units from the centromere. Tentative results suggest that in addition to 'Canthatch', other backcross derivatives of the cultivar 'Thatcher', such as 'Katepwa' and 'Columbus', possess both the suppressor and the inactivated resistance gene(s). Consequently, incorporation of the mutant allele into these cultivars should permit the expression of inhibited resistance.Key words: hexaploid, Triticum, ethyl methanesulphonate, mutant, suppressor, Puccinia graminis.
Inheritance of characters and chromosome number in aneusomatic progeny of Upland cotton (Gossypium hirsutum) of parthenogenetic origin
Authors: Shi-Qi Zhou , De-Qi Qian , Xiu-Yun Cao
Published: April 2011

In this study the inheritance of characters and chromosome number in aneusomatic progeny of Upland cotton of parthenogenetic origin was examined. There was no significant difference in chromosome number between the parents and their selfed offspring in plants with a mean chromosome number of about 26 in somatic cells, whereas plants with about 34 chromosomes showed a larger fluctuation in chromosome number. However, both were relatively stable in character transmission. Why these aneusomatic plants can grow and develop normally and inherit stabilized characters is also discussed in the present article.Key words: Upland cotton (Gossypium hirsutum), aneusomaty, parthenogenetic origin, chromosome number, coefficient of variation.
Plant regeneration and chromosome instability in tissue culture of Elymus canadensis × E. trachycaulus F1 hybrid
Authors: Kumar P. S. , Walton P. D.
Published: April 2011

Callus was induced from pieces of immature inflorescence of a sterile F1 hybrid (2n = 4x = 28) between Elymus canadensis and E. trachycaulus on MS medium supplemented with 2 mg/L of 2,4-D. Calli were of two types: compact or soft. Regeneration occurred predominantly from the compact callus. Although some plantlets were obtained on the callus initiation medium, the frequency of regeneration increased considerably when the callus was transferred to an auxin-free MS medium. Deliberate aging of callus induced cytological instability and variation in chromosome number of the regenerants. Five of the 43 regenerated plants had deviant chromosome numbers, including an octoploid (2n = 8x = 56). Chromosome pairing in the octoploid plant suggests that it originated through chromosome doubling.Key words: callus culture, variation, chromosome number.
Enhanced meiotic chromosome pairing in intergeneric hybrids between Triticum aestivum and diploid Inner Mongolian Agropyron
Authors: Chen Qin , Jahier Joseph , Cauderon Yvonne
Published: April 2011

Triticum aestivum cv. Chinese Spring (2n = 6x = 42, ABD genomes) was crossed with diploid Inner Mongolian Agropyron Gaertn. species A. cristatum and A. mongolicum and reciprocal hybrids between them (2n = 2x = 14, P genome, with or without B chromosomes). Intergeneric hybrids with 2n = 27, 28, 32, and 33 chromosomes were produced by the aid of embryo rescue. The extra chromosomes in two hybrids were assumed to be B chromosomes transmitted by the male Agropyron parent. Average meiotic pairing in the euploid hybrid with 28 chromosomes was 14.38 univalents + 4.92 bivalents + 1.26 trivalents. This level of pairing higher than expected was likely due to homeologous associations between wheat chromosomes. This data indicates that the P genome of diploid as well as tetraploid Agropyron originating from Inner Mongolia possess a genetic system interfering with 5B homoeologous restricting system of wheat.Key words: intergeneric hybrids, Triticum aestivum, diploid Agropyron species, chromosome pairing.
Putative diploid ancestors of 80-chromosome Glycine tabacina
Authors: Singh R. J. , Kollipara K. P. , Ahmad F. , Hymowitz T.
Published: April 2011

The objective of this study was to discover the diploid progenitors of 80-chromosome Glycine tabacina with adventitious roots (WAR) and no adventitious roots (NAR). Three synthetic amphiploids were obtained by somatic chromosome doubling. These were (i) (G. latifolia, 2n = 40, genome B1B1,) × (G. microphylla, 2n = 40, genome BB) = F1(2n = 40, genome BB1) – 0.1% colchicine treatment (CT) – 2n = 80, genome BBB1B1; (ii) (G. canescens, 2n = 40, genome AA) × G. microphylla, 2n = 40, genome BB) = F1 (2n = 40, genome AB) – (CT) – 2n = 80, genome AABB; (iii) (G. latifolia, 2n = 40, B1B1) × G. canescens, 2n = 40, AA) = F1 (2n = 40, genome AB1) – (CT) – 2n = 80, genome AAB1B1. The segmental allotetraploid BBB1B1 was morphologically similar to the 80-chromosome G. tabacina (WAR), but meiotic pairing data in F1 hybrids did not support the complete genomic affinity. Despite normal diploid-like meiosis in allotetraploids AABB and AAB1B1, AABB was completely fertile, while pod set in AAB1B1 was very sparse. Morphologically, allotetraploid AABB was indistinguishable from the 80-chromosome G. tabacina (NAR) but in their F1 hybrids, the range of univalents at metaphase I was wide (4–44). The allotetraploid AAB1B1 did not morphologically resemble the 80-chromosome G. tabacina (NAR). However, the F1 hybrid of AABB × AAB1B1 showed normal meiosis with an average chromosome association (range) of 1.7 I (0–4) + 39.2 II (38–40). Based on this information, we cannot correctly deduce the diploid progenitor species of the 80-chromosome G. tabacina (NAR). The lack of exact genome homology may be attributed to the geographical isolation, natural mutation, and growing environmental conditions since the inception of 80-chromosome G. tabacina. Thus, it is logical to suggest that the 80-chromosome G. tabacina (NAR) is a complex, probably synthesized from A genome (G. canescens, G. clandestina, G. argyrea, G. tomentella D4 isozyme group) and B genome (G. latifolia, G. microphylla, G. tabacina) species, and the 80-chromosome G. tabacina (WAR) complex was evolved through segmental allopolyploidy from the B genome species.Key words: Glycine spp., allopolyploidy, colchicine, genome, intra- and inter-specific hybridization, polyploid complex.
Interspecific hybridization between Elymus himalayanus and E. schrenkianus, and other Elymus species (Triticeae: Poaceae)
Authors: Lu Bao-Rong , Bothmer Roland Von
Published: April 2011

To determine the genomic constitutions of Elymus himalayanus (Nevski) Tzvelev (2n = 4x = 42) and E. schrenkianus (Finch. &Mey.) Tzvelev (2n = 6x = 42), interspecific hybridizations were carried out between the two species, and with 10 other Elymus species containing the "SH," "SY," and "SHY" genomes, respectively, viz., E. tsukushiensis Honda, E. caninus (L.) L., E. semicostatus (Nees ex Steud.) Meld., E. parviglumis (Keng) Löve, E. pseudonutans Löve, E. brevipes (Keng) Löve, E. tibeticus (Meld.) G. Singh, E. shandongensis B. Salomon, E. gmelinii (Ledeb.) Tzvelev, and E. abolinii (Drob.) Tzvelev. Meiotic pairing was analyzed in the parents and interspecific hybrids. It is concluded from this study that (i) both E. himalayanus and E. schrenkianus are allohexaploid species and contain the "S," "H," and "Y" genomes in a slightly modified form, (ii) there exists a low homoeology between the different genomes, and (iii) the "SY" genomes are differentiated among the tetraploid Elymus species.Key words: interspecific hybridization, Triticeae, Elymus species, meiotic pairing, genome.
Polytene chromosomes of the Old World screwworm fly (Chrysomya bezziana) and its evolutionary relationships with Lucilia cuprina and Cochliomyia hominivorax (Diptera: Calliphoridae)
Authors: Bedo D. G.
Published: April 2011

Standard polytene chromosome maps for the Old World screwsworm fly, Chrysomya bezziana, are presented. Good quality polytene chromosomes obtainable from pupal trichogen cells allow detailed analysis of autosomal euchromatin. The sex chromosomes are represented by irregular heterochromatic structures resembling those described previously in trichogen polytene chromosomes of the Australian sheep blowfly, Lucilia cuprina. A high degree of homology with the banding pattern of L. cuprina polytene chromosomes allowed direct recognition of approximately 60% of the L. cuprina complement in the C. bezziana maps. A further 13% may be homologous. The extensive homology observed is discussed in relation to the rate of chromosome rearrangement and conservation of karyotype elements in the evolution of Calliphorid flies. The observed conservation in polytene banding patterns should facilitate construction of phylogenies over a number of generic groups.Key words: Chrysomya bezziana, screwworm, polytene map, chromosome homology.
Studies of a spontaneous lethal mutation at the albino locus in SELH/Bc mice
Authors: Juriloff D. M. , Harris M. J. , Wong V. , Miller J. E.
Published: April 2011

We report a new mutation at the albino locus in SELH/Bc mice. The mutation arose spontaneously in a male mouse that appeared to be a somatic and germ line mosaic for a new albino (c) allele, provisionally named cBc. The mutation is a recessive lethal, causing embryonic death soon after implantation. We have shown that there is no detectable activity of the Mod-2 allele in cis with the mutation and conclude that the mutation is probably a deletion that includes the c locus, the Mod-2 locus, the intervening 2 cM, and at least one locus essential for postimplantation embryonic survival, either proximal to the c locus or distal to the Mod-2 locus. This new mutation is similar to most previously reported spontaneous mutations at the albino locus in that it arose in a somatic and germ line mosaic mutant animal but differs from them in that it is an embryonic lethal when homozygous and is apparently a deletion. SELH/Bc mice appear to have a high mutation rate. This lethal albino mutation that appears to be a postmeiotic deletion should be useful in the search for the mechanism of mutagenesis in SELH/Bc mice. It may also be useful in mapping essential genes in the c-locus region.Key words: embryonic lethal, mosaic, deletion.
Relationships between amino acid sequences determined through optimum alignments, clustering, and specific distance patterns: application to a group of scorpion toxins
Authors: Tyson Hugh
Published: April 2011

Optimum alignment in all pairwise combinations among a group of amino acid sequences generated a distance matrix. These distances were clustered to evaluate relationships among the sequences. The degree of relationship among sequences was also evaluated by calculating specific distances from the distance matrix and examining correlations between patterns of specific distances for pairs of sequences. The sequences examined were a group of 20 amino acid sequences of scorpion toxins originally published and analyzed by M.J. Dufton and H. Rochat in 1984. Alignment gap penalties were constant for all 190 pairwise sequence alignments and were chosen after assessing the impact of changing penalties on resultant distances. The total distances generated by the 190 pairwise sequence aligments were clustered using complete (farthest neighbour) linkage. The square, symmetrical input distance matrix is analogous to diallel cross data where reciprocal and parental values are absent. Diallel analysis methods provided analogues for the distance matrix to genetical specific combining abilities, namely specific distances between all sequence pairs that are independent of the average distances shown by individual sequences. Correlation of specific distance patterns, with transformation to modified z values and a stringent probability level, were used to delineate subgroups of related sequences. These were compared with complete linkage clustering results. Excellent agreement between the two approaches was found. Three originally outlying sequences were placed within the four new subgroups.Key words: sequence alignment, specific distances, sequence relationships.
Ribosomal DNA repeat unit polymorphism in six Aegilops species
Authors: Kim W. K. , Innes R. L. , Kerber E. R.
Published: April 2011

Total genomic DNA of 27 accessions representing six Aegilops species was restricted with BamHI, EcoRI, and BamHI plus EcoRI, and the restriction fragments were probed with the ribosomal clones pMF2 containing the ribosomal RNA coding regions. The rDNA repeat lengths varied between 9.0 and 10.8 kb. Intraspecific variation among the 10 accessions of Ae. squarrosa var. strangulata ranged from 9.0 to 9.6 kb, suggesting a diversity of genotypes within as well as between species. These variations were not related to their geographical distributions. Each of 24 accessions had two BamHI sites in the coding region (type A), while three accessions of Ae. squarrosa var. strangulata had four BamHI sites (type B, two sites in the intergenic region). Results for these three accessions of Ae. squarrosa var. strangulata suggest genotypic diversity in this species. In BamHI restriction of each accession, a third DNA fragment, ranging between 9.0 and 10.8 kb in type A and 6.0 kb in type B, resulted from lack of digestion at the 26S BamHI site. In double digestion, all rDNA repeat units were restricted by EcoRI, yielding 3.9-, 0.9-, and 4.8-kb fragments, the last of which arose from the lack of digestion at the 26S BamHI site, estimated to occur in 5–20% of the repeat units, depending on the accession.Key words: Triticum tauschii, RFLP, diversity.
The RSS system of unidirectional cross-incompatibility in maize. 2. Cytology
Authors: Rashid Abdul , Peterson Peter A.
Published: April 2011

In 1975, a number of genetic lines discovered in our maize genetics nursery in Ames, Iowa, showed unidirectional cross-incompatibility. Later, it was found that this unidirectional cross-incompatibility is controlled by three recessive genes. One locus (cif) controls the incompatibility reaction in the female tissue and the other two (cim1 and cim2) control the incompatibility reaction in the pollen grain. The cross is incompatible only when the female parent is homozygous recessive for the cif and the male parent is homozygously recessive for the cim1 as well as the cim2 locus. Cytological studies of this unidirectional cross-incompatibility show that the site of the incompatibility reaction occurs after the entry of the pollen tubes into the transmitting tract of the incompatible silks. Between 12 and 24 h after pollination, the incompatible pollination is characterized by the swelling and bursting of pollen tubes at the tip, after which pollen tube growth stops.Key words: maize, pollen tube, cross-incompatibility.
The effect of colchicine on meiosis in the Rhoeo discolor stabile complex translocation heterozygote
Authors: Verma R. C. , Vyas P. , Raina S. N.
Published: April 2011

Rhoeo discolor (2n = 12) was used to study the effect of colchicine on chromosome pairing during meiosis. Pachytene pairing appeared unaffected, but only 17.5% of the PMCs formed a ring of 12 chromosomes at metaphase I of meiosis. While 27.5% of cells had a complete chain of 12, 49.0% had chain configurations of varying (2–11) number of chromosomes and 6.0% had complete univalence. Adjacent orientation was found in the majority of cells with chain complexes of 2–11 chromosomes. The result was highly disturbed anaphase I where 58.4% PMCs were abnormal. It is concluded that the presence of aberrant cells at metaphase I is either due to colchicine-induced ineffectiveness of pairing at the very small pairing regions or failure of chiasma formation.Key words: colchicine, meiosis, Rhoeo discolor, translocation heterozygote, univalents, alternate/adjacent orientation.
Recent amplification of triose phosphate isomerase related sequences in lettuce
Authors: Paran Ilan , Kesseli Richard V. , Westphal Lore , Michelmore Richard W.
Published: April 2011

A random cDNA clone was identified as distinguishing near-isogenic lines for downy mildew resistance in lettuce. The clone detected multiple restriction fragments in genomic Southern blots of lettuce. Restriction fragment length polymorphisms (RFLPs) detected by this clone mapped to separate clusters of resistance genes; therefore, these sequences were studied in a greater detail. Sequence analysis indicated that the cDNA encoded the glycolytic enzyme triose phosphate isomerase (TPI). The lettuce clone shares 85% sequence similarity at the amino acid level with TPI from maize. TPI-related sequences were mapped in lettuce using three crosses. Ten loci were distributed in six linkage groups. Possible mechanisms of amplification and dispersion were investigated. Retrotransposition was excluded, since intron five is retained in all TPI-related genomic sequences. Large scale chromosomal rearrangements were not involved, as RFLP markers flanking TPI loci were not duplicated. A high level of genomic variability was detected by the TPI clone; 37 different restriction fragments were detected in Southern hybridizations to 64 populations of lettuce including 47 cultivars of Lactuca sativa and five wild species. Species distantly related to L. sativa had few TPI loci, indicating that their amplification and dispersion were recent and had occurred after the emergence of the L. serriola complex.Key words: triose phosphate isomerase, gene duplication, lettuce.
Méthode d'étude des quantités d'ADN métaphasique après écrasement de méristèmes radiculaires
Authors: Coq C. Le , Guervin C. , Esclapez M. , Moret J.
Published: April 2011

A method is described for standardized preparation of meristematic root cells treated with colchicine for cytophotométrie analysis of metaphase DNA. Deoxyribonucleic acid has been stained by the Feulgen reaction prior to crushing of the cells.Key words: cytophotometry, Ornithogalum, nuclear DNA content.