bluuebunny/crossref_metadata_2025 huggingface dataset:
Genome analysis in wheat – rye – Aegilops caudata trigeneric hybrids
Authors: Orellana J. , Vazquez J. F. , Carrillo J. M.
Published: April 2011

Using C-banding, homologous and homoeologous meiotic pairing between wheat (AB), rye (R), and Aegilops caudata (C) genomes were estimated at meiotic metaphase I in trigeneric hybrids (AABBRC; 2n = 6x = 42). In all hybrids, the C-genome chromosomes pair homoeologously only with chromosomes of the A genome, but not with chromosomes of the B genome or R genome. The A – C pairing was restricted to trivalents (0.15 per cell), each composed of two A-genome and one C-genome chromosomes. These preliminary data suggest that the C genome of Ae. caudata is probably more closely related to the A genome than to the B genome of wheat.Key words: trigeneric hybrid, wheat, rye, Aegilops, genome analysis, meiosis.
Genotype and the cryopreservation process affect the levels of aneuploidy and chromosome breakage in cultured human fibroblasts
Authors: Rudd N. L. , Hoar D. I. , Williams S. E. , Hennig U. G. G.
Published: April 2011

Spontaneous micronucleus frequencies were measured in 11 human fibroblast strains, with early-passage cells that had never been frozen and with cells of comparable population doublings that had been cryopreserved in liquid nitrogen. The mean micronucleus frequency of the 11 strains increased from 14.0 ± 0.7 to 20.4 ± 1.8/1250 mononucleated cells (P = 0.002) after the freeze – thaw process. The nature of this increase in micronucleus frequency was examined using an immunodetection assay for the in situ identification of kinetochores in micronuclei. The increase in micronucleus frequency occurred primarily in the kinetochore-positive fraction, which is indicative of aneuploidy, but also by an increase in chromosome breakage in several strains. The findings were reproducible in repeat biopsies from two donors. Plating efficiencies of the 11 strains were studied during 1 – 9 and 10 – 20 population doublings from primary outgrowth, before freezing and again after freeze – thaw. The mean plating efficiency of frozen – thawed cells before nine doublings was significantly lower than that of cells of similar ages that had never been frozen (P = 0.004). The four strains that had a greater than 25% decrease in plating efficiency post freeze-thaw also had the highest aneuploidy index post freeze-thaw, suggesting that chromosomal imbalance contributes to the observed reduction in growth. We conclude that the genotype and culture manipulations of a fibroblast strain influence the outcome of the micronucleus assay.Key words: micronuclei, kinetochore immunofluorescence, freeze – thaw, aneuploidy, chromosome breakage.
Breaking up the chromosomes of Baetica ustulata by in situ treatments with restriction endonucleases
Authors: Sentís C. , Santos J. , Fernández-Piqueras J.
Published: April 2011

Fixed chromosomes of Baetica ustulata were treated with restriction endonucleases and subsequently stained with either Giemsa or the DNA-specific dye propidium iodide. Each enzyme produces a specific banding pattern with both dyes, which demonstrates the value of restriction endonucleases for chromosome banding in this species. The results obtained agree with the hypothesis that the action of restriction enzymes is based on cutting and extraction of DNA and is essentially determined by DNA base composition rather than by chromatin structure. However, strictly centric bands could be an exception. At least nine chromatin types can be distinguished in B. ustulata according to their different response to enzyme digestion and to the fluorescence banding patterns. Differential digestion of specific heterochromatic areas in band 4.4 and in the supernumerary segment of M5 by the HpaII – MspI enzyme pair suggests a high level of DNA methylation at these regions. The distribution of the different classes of DNA repeated sequences in the chromosome complement of B. ustulata indicates that some bands seem to follow the general principles of heterochromatin equilocality, while conceited evolution of heterochromatic DNA in other regions might have different rates of convergence in this species.Key words: restriction endonucleases, chromatin heterogeneity, methylated bands, equilocality, concerted evolution.
Intergeneric hybrids of Triticum aestivum × Leymus multicaulis
Authors: Plourde A. , Comeau A. , Fedak G. , St-Pierre C.-A.
Published: April 2011

Hybrids were obtained at a frequency of 0.53% of the pollinated florets by pollination of Triticum aestivum (2n = 6x = 42, AABBDD) cv. Norin 29 with Leymus multicaulis (2n = 4x = 28, JJNN). The hybrid plants were taller than both parents and the floral structure of the hybrid spike resembled a modified wheat spike. The hybrids had the expected somatic chromosome number of 35 (ABDJN). The average bivalent frequency per cell at metaphase I in the meiocytes was very low, 0.59 and 0.45, respectively, for the two hybrids studied, suggesting the absence of homology between the parental genomes. The meiotic abnormalities observed consisted of lagging chromosomes and cytokinesis irregularities, leading to the production of polyads containing micronuclei at the quartet stage. The backcrossing of one hybrid to wheat cv. Fukuho resulted in the production of one plant with 56 chromosomes. Preliminary results on the evaluation of the BC3 and BC2F2 derivatives for barley yellow dwarf virus resistance (BYDV) suggested that the transfer of BYDV resistance genes from L. multicaulis to wheat is possible.Key words: intergeneric hybrids, Leymus, wheat, rye-grass, wild rye, embryo rescue.
A potential solution to the chromosome instability problem in hexaploid alfalfa, Medicago sativa L.
Authors: McCoy T. J.
Published: April 2011

Autohexaploid alfalfa (2n = 6x = 48) is chromosomally unstable, which prevents commercial use. The objective of this investigation was to test whether synthesizing Medicago hexaploids (2n = 6x = 48) that are alloautohexaploids results in chromosomally stable hexaploid populations. Previous research in our laboratory demonstrated a lack of affinity between the genomes of alfalfa and M. papillosa Boiss. Triploid (2n = 3x = 24) interspecific hybrids with two M. papillosa genomes and one genome of M. sativa were readily recovered from seed following the cross (2x) M. sativa × (4x) M. papillosa. For this study, the triploids were chromosomally doubled to produce alloautohexaploids, and these alloautohexaploids were used to test chromosome stability in hexaploids with no more than four homologous genomes. Chromosome counts of 47 progeny from intercrossing the alloautohexaploids demonstrated all were hexaploid, indicating chromosome stability. Designing novel genomic combinations based on genomic affinity may result in higher yielding alfalfa populations that have a modified cytogenetic structure.Key words: Medicago cancellata, Medicago papillosa, Medicago saxatilis, genomic affinity, hexaploids.
DNA analyses in wheat breeding
Authors: Clarke B. C. , Moran L. B. , Appels R.
Published: April 2011

A simplified procedure of sample preparation for the isolation of DNA (accessible to restriction fragment length polymorphism, RFLP, mapping) from wheat leaf material is presented. The procedure utilizes a sap extractor and approximately 500 samples can be processed in 1 week. The ability to handle this number of samples makes it feasible to interact with a plant breeding programme when a particularly valuable DNA marker is available. Three examples of analysing large populations are presented to demonstrate the application of the modified procedure to isolating DNA from wheat leaves.Key words: techniques, restriction fragment length polymorphism, genomic DNA isolation.
Sex chromosome evolution and population differentiation in the Eusimulium aureum group of black flies
Authors: Leonhardt K. G. , Feraday R. M.
Published: April 2011

The pattern of sex-chromosome variation within and between species of the Eusimulium aureum species group of black flies is examined and used to support the argument that speciation in black flies is often an adaptive process. A pair of homosequential species in this group is presented as an exceptional case in black flies that does not argue against the chromosomally mediated speciation model.Key words: black flies, sex chromosomes, evolution.
Isozymes of amylase, alcohol dehydrogenase, malic enzyme, malate dehydrogenase, and superoxide dismutase in Chloealtis conspersa (Orthoptera)
Authors: Moens Peter B. , Kolodziejczyk Steven
Published: April 2011

Five enzymes of the grasshopper Chloealtis conspersa were studied for possible gene linkage. Because of the extreme localization of chiasmata throughout most of the genome of C. conspersa, it was expected that genes would appear either to be completely linked or to assort independently. Our results indicate that malic enzyme and alcohol dehydrogenase are probably on the X chromosome. Superoxide dismutase is produced from the product of duplicate genes where Sod 1-1 is monomorphic and Sod 1-2 has two alleles, one producing a fast-migrating band on gel electrophoresis and one a slow band. While amylase, malate dehydrogenase, and superoxide dismutase appeared to be autosomal, there was no evidence of linkage between them.Key words: Chloealtis conspersa, amylase, alcohol dehydrogenase, malic enzyme, malate dehydrogenase, superoxide dismutase.
The influence of cell size and chromosome dosage on cold-hardiness expression in the Triticeae
Authors: Limin A. E. , Fowler D. B.
Published: April 2011

The influence of cell size and chromosome dosage on cold-hardiness expression was investigated in members of the tribe Triticeae. Mean leaf guard-cell lengths for ploidy levels of 2x, 4x, 6x, and 8x were found to increase by approximately 10 μm with each addition of two basic (x = 7) genomes, indicating that larger cell size was associated with higher ploidy level. Poor expression of cold hardiness in amphiploids was associated with large cell size. However, comparisons among and within species indicated that ploidy level was not the only factor determining cell size. Significant differences in guard-cell length were observed among common wheat (Triticum aestivum L. em. Thell.) cultivars. Cell size differences among cultivars were found in both hardened and nonhardened common wheat plants and these differences were associated with cultivar cold hardiness (r = 0.95, P ≤ 0.01). The evidence indicated that smaller cell size influenced cold tolerance by amplifying the expression of cold-hardiness genes in cold-acclimated plants, probably by reducing the degree of cell contraction from freeze dehydration. A chromosome (gene) dosage effect that favored the expression of genes from the parent species contributing the higher chromosome number was also shown to play an important role in the expression of cold hardiness in interspecific hybrids and amphiploids. Comparison of related species with similar cell size and chromosome number suggested differences in the effectiveness of cold hardiness conferring genes. Observations made on species from the Triticeae indicate that when cold-hardiness potential is limited at the diploid level, a plant group may expand its cold-hardiness range by "loading up" on existing cold-hardiness genes by means of polyploidy. An increased genetic potential may then be further enhanced by selection for smaller cell size within the polyploid nucleotype. This process appears to have been responsible for the superior cold hardiness of hexaploids within the Triticum genus.Key words: cell size, cold hardiness, gene dosage, Triticeae, evolution, interspecific hybrid, Agropyron.
A model of meiotic chromosome association in tetraploids
Authors: Crane Charles F. , Sleper David A.
Published: April 2011

A model is constructed for chromosome association at meiotic metaphase I in tetraploids. Probabilities are estimated for each pachytene configuration and for subsequent formation of at least one chiasma in each combination of chromosome arms. Long and short arms can differ but are related through an effective arm ratio so as to maintain the same pattern of genomic affinity for both arms. No other a priori assumptions are made about the pattern of genomic affinity, but the same basic assumptions are made as in our preceding model for triploids. The model is statistically overparameterized and therefore has multiple solutions whose range can be found through repeated optimization from different starting points. In some cases the same expected meiotic analysis can arise from quite different genomic structures, which therefore cannot be distinguished on the basis of unmarked chromosomes. Solutions to the model are conveniently expressed in terms of the proportion of metaphase I association due to each pairwise combination of genomes. Interpretation of model solutions is also aided by the use of numerical indices that reflect closeness to 11 particular genomic structures or that reveal properties of the relationship among variables. The model differs from that of Kimber and Alonso in its handling of two chiasmatically bound arms in a randomly pairing homologous group, and frequently as well in its optimized pattern of genomic affinity upon application to 3:1 and 2:1:1 genomic structures. With the aid of the model, genomic affinity is analyzed in 20 individuals, representing hybrids, amphiploids, and species.Key words: polyploidy, genome analysis, preferential pairing, meiotic model.
Ancestors of 80- and 78-chromosome Glycine tomentella Hayata (Leguminosae)
Authors: Singh R. J. , Kollipara K. P. , Hymowitz T.
Published: April 2011

The objective of this study was to determine the progenitors of 80- and 78-chromosome tomentellas of the subgenus Glycine. Wide geographical distribution, aggressive and vigorous growth habit, diploid-like meiosis in the accessions, and meiotic pairing in intraspecific and interspecific hybrids suggested that both cytotypes (2n = 80, 78) evolved through allo-polyploidization. Two synthetic amphidiploids were obtained by somatic chromosome doubling ((G. tomentella, 2n = 40, genome DD) × (G. canescens, 2n = 40, genome AA) = F1, (2n = 40, genome AD), which was treated with colchicine, giving 2n = 80, genome AADD; (G. tomentella, 2n = 38, genome EE) × (G. canescens, 2n = 40, genome AA) = F1, (2n = 39, genome AE), which was treated with colchicine, giving 2n = 78, genome AAEE). These amphidiploids, which exhibited gigas effect, diploid-like meiosis, and normal pollen and seed set, were hybridized with 80- and 78-chromosome tomentellas. On the basis of morphological characteristics and meiotic pairing in F1 plants, G. tomentella (2n = 40, DD) and G. canescens (2n = 40, AA) are concluded to be the ancestors of 80-chromosome tomentellas (AADD) from Queensland, Australia. One of the ancestors of 80-chromosome tomentellas from Northern Territory and Western Australia, Australia, and Papua New Guinea is G. canescens; the second progenitor species was not determined. In addition, it is apparent that both 40- and 38-chromosome tomentellas gave rise to 78-chromosome G. tomentella (DDEE).Key words: allopolyploidy, colchicine, genome, intraspecific and interspecific hybridization, polyploid complex.
Synaptonemal complex analysis of hybrid cattle. I. Pachytene substaging and the normal full bloods
Authors: Dollin A. E. , Murray J. D. , Gillies C. B.
Published: April 2011

Meiotic chromosome pairing abnormalities in full-blood and hybrid Bos taurus and B. indicus cattle have been surveyed by electron microscopy of pachytene synaptonemal complex spreads. In this paper, the full-blood spreads are described in detail, including the use of XY and nucleolar morphology and other measured parameters for pachytene substaging. Pairing abnormalities were observed in up to 9% of the full-blood spreads. Most of these pairing abnormalities (83%) occurred in early-pachytene spreads, suggesting that the mechanism of synaptic adjustment may operate in cattle.Key words: synaptonemal complex, cattle, pachytene substages.
Genetic and cytogenetic analyses of the A genome of Triticum monococcum L. V. Inheritance and linkage relationships of genes determining the expression of 12 qualitative characters
Authors: Kuspira J. , Maclagan J. , Bhambhani R. N. , Sadasivaiah R. S. , Kim N.-S.
Published: April 2011

Our investigation of 460 true-breeding lines confirms a long-standing observation that natural phenotypic and genetic variability in the diploid wheat Triticum monococcum L. is limited. The modes of inheritance of 12 morphological characters are discussed in light of the extensive information available on the genetics and cytogenetics of many of these characters in the related wheat Triticum aestivum. Analysis of data from appropriate crosses, complementation studies, and observations of phenotypes of F1s and F2s from crosses between lines expressing dominant traits indicate that each of these characters is determined by one major gene. A multiple allelic series exists at each of the Hg (glume pubescence) and Hn (node pubescence) loci. The genes for six of these characters fall into two closely linked groups. Genes Bg (glume colour) and Hg are the same distance apart as in Triticum aestivum, indicating that at least this segment of chromosome 1A has been highly or completely conserved since the origin of the polyploid wheats. The genes Sg (glume hardness), La (lemma awn length), Fg (false glume), and Lh (head type) are also very closely linked, with the outside markers being only 4 map units apart. The dominant and recessive alleles of genes determining these characters should serve as excellent markers for linkage and chromosomal mapping because of their complete penetrance and constant expressivity. Tentative assignments of genes and linkage groups identified in this investigation to specific chromosomes of T. monococcum have been made on the basis of known chromosomal locations of A genome genes in T. aestivum. The tentative assignments could be verified using a variety of genetic and cytogenetic approaches. It is suggested that a thorough study of the genetic heritage of einkorn wheat will require the use of induced mutants since natural genetic variability is low in this species.Key words: Triticum, characters, inheritance, linkage, mapping, A genome.
Karyotype and achiasmatic female meiosis in Helicoverpa armigera (Hübner) and H. punctigera (Wallengren) (Lepidoptera: Noctuidae)
Authors: Fisk Jennifer H.
Published: April 2011

The economically important pest species Helicoverpa armigera and H. punctigera have a karyotype consisting of 31 pairs of chromosomes. The chromosomes are in a graded series of sizes such that pairs cannot be differentiated. Cytological evidence suggests that female meiosis is achiasmatic. Precocious separation of bivalents into univalents at metaphase I was observed in some spermatocytes of H. punctigera. This species also had a consistently greater number of bivalents with fully terminalised chiasmata in each spermatocyte at male metaphase I than H. armigera.Key words: Lepidoptera, Helicoverpa, achiasmatic meiosis, karyotype.
Quantitative analysis of silver staining of the nucleolar organizing region in Eliomys quercinus
Authors: Sánchez A. , Burgos M. , Jiménez R. , Guardia R. Díaz de la
Published: April 2011

In somatic cells of the rodent Eliomys quercinus (dormouse) nucleoli are found on chromosomes 14 and 22. Variation in silver stainability of nucleolar organizing regions at metaphase was concluded to reflect variation in nucleolar activity in the preceding interphase. It could be demonstrated that variation in nucleolar organizing region stainability was not independent for the two homologues of the same chromosome, nor for different chromosomes, but the interactions were complex. This is suggested to reflect a mechanism of regulation of nucleolar activity. The interactions between nucleolar organizing regions varied among individuals.Key words: Eliomys quercinus, nucleolar organizing regions, nucleolar organizing region activation.
Miniature genomes and endopolyploidy in cladoceran crustaceans
Authors: Beaton Margaret J. , Hebert Paul D. N.
Published: April 2011

The haploid genome sizes (0.37 and 0.47 pg) of two members of the cladoceran crustacean genus Daphnia rank among the smallest known for Crustacea. An examination of cladoceran somatic tissues by scanning microdensitometry revealed abundant endopolyploidy in both species. Although cells in the labrum possessed the highest DNA content (1024C), endopolyploid cells (4–512C) were widely distributed throughout the body. Daphnia pulex and D. magna exhibited similar ploidy levels in most tissues, but differences between the two species were noted in the epidermis and labrum. The prevalence of polyploid nuclei suggests that endopolyploidy is an important process in organisms whose genomes have been miniaturized by nucleotypic selection.Key words: somatic polyploidy, genome size, Daphnia, ploidy shifts, macroevolution.
Stability of ploidy in meristems of plants regenerated from anther calli of wheat (Triticum aestivum L. em. Thell.)
Authors: Kudirka Dalia T. , Schaeffer Gideon W. , Baenziger P. Stephen
Published: April 2011

Plants were regenerated from anther calli of the winter wheat cultivar 'Centurk' (Triticum aestivum L. em. Thell.). Cells of root tips of young regenerated plants were assayed for ploidy and plants were categorized as polyhaploid, mixoploid, or hexaploid. Tillering and seed set were analyzed in plants that survived to maturity. Less than 1% of the tiller population produced by polyhaploid plants set seed. In contrast, 73% of the tiller population produced by hexaploid plants set seed, with significantly greater seed set per fertile tiller. These data were taken to indicate that the ploidy composition of root tips of young regenerated plants reflected that of the reproductive structures of mature regenerated plants. Common patterns of aneuploidy in hexaploid and hyperploid cells found among roots of individual plants confirmed the idea that doubling of the cell genome occurred before plant regeneration. Polyhaploid and hexaploid cells were found in individual root tips of mixoploid plants regenerated from calli that were known to be cytochimeric. The possibility that regeneration of plants can occur from more than a single cell of an anther callus is discussed.Key words: anther culture, Triticum aestivum, wheat, mixoploidy, aneuploidy, regeneration.
Screening of durum wheats for pasta-making quality with monoclonal antibodies for gliadin 45
Authors: Howes N. K. , Kovacs M. I. , Leisle D. , Dawood M. R. , Bushuk W.
Published: April 2011

Monoclonal antibodies specific for gliadin band 45 (gli 45) of common wheat cultivar 'Marquis' were treated against durum wheat gliadins using an enzyme-linked immunosorbent assay (ELISA). In a test of 15 durum cultivars, high ELISA values were associated with gli 45, high gluten strength, and high sodium dodecyl sulfate (SDS) sedimentation volume; low ELISA values were associated with gli 42, low gluten strength, and low SDS-sedimentation volume. Analysis of 120 F5 lines from the backcrosses Ward/Vic//Vic and Ward/Vic//Ward confirmed that a high reaction to ELISA was statistically correlated with the presence of gli 45, with high gluten strength, and with high SDS-sedimentation volume. It was concluded that monoclonal antibodies specific for gli 45 have potential as a test for rapid screening of durum wheat breeding populations for desirable pasta-making quality.Key words: monoclonal antibodies, gliadin, enzyme-linked immunosorbent assay, durum wheat.
Distribution of polyploid variation in big bluestem (Andropogon gerardii, Poaceae) across the tallgrass prairie region
Authors: Keeler Kathleen H.
Published: April 2011

The objective of this research was to describe the distribution of polyploid cytotypes of the grass big bluestem (Andropogon gerardii Vitman) along an east–west transect across the tallgrass prairie region, as an integral part of understanding the function of intraspecific polyploid polymorphism. Andropogon gerardii shows intraspecific variation in amount of nuclear DNA as a result of intraspecific polyploidy. Nearly 600 plants from 15 prairies in 5 states were collected and nuclear DNA was determined by flow cytometry. In the eastern part of the tallgrass prairie region, higher polyploids were rarely found. However, at the western edge of the tallgrass prairie, west of the Missouri River, plants with high nuclear DNA values comprised about half of the plants sampled and in one native prairie formed 82% of the population. Although big bluestem is historically the dominant grass throughout this region, it is extremely variable only on the western extreme of region.Key words: polyploidy, polymorphism, big bluestem, Poaceae, Andropogon gerardii, tallgrass prairie.
Cytogenetic studies of progeny from the intergeneric crosses Elymus × Hordeun and Elymus × Secale
Authors: Lu Bao-Rong , Salomon Björn , Bothmer Roland von
Published: April 2011

Meiotic pairing was studied in three Elymus species, E. pseudonutans (2n = 28), E. shandongensis (2n = 28), and E. semicostatus (2n = 28), as well as their dihaploids (2n = 14) which were produced from the intergeneric crosses E. pseudonutants × Hordeum vulgare ssp. spontaneum, E. shandongensis × Triticum aestivum, and E. semicostatus × H. bulbosum. An average of 12.82 I + 0.55 II + 0.03 III; 12.59 I + 0.65 II + 0.01 III, and 12.70 I + 0.76 II + 0.02 III per cell characterized meioses in the dihaploids, respectively. Intergeneric hybrids (2n = 21) of the three species were also obtained with diploid Secale cereal and S. montanum. Meiotic configurations of the hybrids were 14.64 I + 2.82 II + 0.20 III + 0.01 IV and 16.38 I + 2.02 II + 0.16 III for two combinations of E. pseudonutans × S. cereale; 15.59 I + 2.62 II + 0.08 III and 19.63 I + 0.65 II for E. shandongensis × S. cereale and E. semicostatus × S. montanum, respectively. A large number of chromosomes were involved in secondary associations in the different combinations. The study revealed (i) low affinity between S and Y genomes in the investigated Elymus species, (ii) a certain degree of homoeology between genomes of Elymus (S or Y) and rye (R), and (iii) that the rye genome affects homoeologous chromosome pairing between different genomes in the Elymus species.Key words: Elymus, Hordeum, Secale, dihaploid, chromosome elimination, intergeneric hybrid, meiotic pairing.
Two autosomal trisomies in the horse: 64,XX, −26, +t(26q26q) and 65,XX, +30
Authors: Bowling A. T. , Millon L. V.
Published: April 2011

The phenotypic effects in a yearling Arab filly of a newly described equine autosomal trisomy syndrome for chromosome 30 (65,XX, + 30) consisted of small size and severe angular deviation of front legs accompanied by mild Polydactyly, but no mental dullness. This case was associated with advanced maternal age. Additional banding studies of a second trisomy case confirmed the assignment to chromosome 26 (64,XX, −26, +t(26q26q)) and evidence of her fertility was presented.Key words: autosomal trisomy, chromosomes, cytogenetics, horse karyotyping, trisomy.
Genetic control of 1R nucleolus organizer region expression in the presence of wheat genomes
Authors: Vieira Rita , Queiroz Álvaro , Morais Leonor , Barão Augusta , Mello-Sampayo T. , Viegas Wanda
Published: April 2011

The expression of rRNA genes located in the nucleolar organizing region (NOR) present on the short arm of chromosome 1R from rye (Secale cereale L.) was examined in several hexaploid (Triticum aestivum L.) and tetraploid wheats (Triticum turgidum L.) containing the entire chromosome 1R from rye (disomic substitution 1B(1R)), its full haploid genome (hexaploid wheat–rye F1 hybrid), or only its short arm translocated to the long arms of wheat chromosomes from the homoeologous group 1 (disomic translocations 1AL/1RS, 1BL/1RS, or 1DL/1RS) or added to the complete hexaploid wheat genotype (monotelosomic addition 1RS). By silver staining and determination of the number of Ag-NORs and the average number of nucleoli per root-tip cell it became apparent that the expression of 1R NORs, in the presence of wheat genomes, depends on the absence of the long arm of rye chromosome 1R. In wheat-rye F1 hybrids and in hexaploid wheat with a disomic substitution 1B(1R), 1R NOR was morphologically absent, even when only one wheat major NOR was present, in contrast with its frequent expression in wheat–rye translocation or addition lines where only its short arm was added. It is suggested that wheat nucleolar dominance over rye as expressed by heterochromatic and silent NOR in 1RS is under a complex genetic control which involves interaction between 1RL and unidentified wheat genes.Key words: 1R nucleolus organizer region, gene activity, amphiplasty.
A cytogenetic analysis of the chromosomes in two related species of the genus Muscari (Liliaceae)
Authors: Rejón C. Ruiz , Lozano R. , Rejón M. Ruiz
Published: April 2011

Muscari comosum L. and Muscari matritensis Ruiz Rejón et al. are two closely related species of the subgenus Leopoldia, belonging to the genus Muscari (Liliaceae). Cytogenetic analyses have been made to analyse the differences between these species. Major differences are that M. comosum has four or five dark intercalary 4,6-diamidino-2-phenylindole (DAPI) positive C-bands in the first chromosome pair, whereas M. matritensis has only three thin bands. Muscari comosum has a large chromomycin A3 positive C-band in the fifth, nucleolus organizing region (NOR) bearing chromosome pair, whereas M. matritensis has the CMA3-positive band and the NOR in the short arm of the second pair. The possible role played by occurrences of translocations and amplifications in the chromosomal evolution of these species is discussed.Key words: Muscari, Liliaceae, karyotypes, evolution.
The initiation of meiotic chromosome pairing: the cytological view
Authors: Loidl Josef
Published: April 2011

Opposing views are held with respect to the time when and the mechanisms whereby homologous chromosomes find each other for meiotic synapsis. On the one hand, some evidence has been presented for somatic homologous associations or some other kind of relationship between chromosomes in somatic cells as a preliminary to meiotic pairing. On the other hand, it is argued by many that homologous contacts are first established at meiotic prophase prior to, or in the course of, synaptonemal complex formation. The present paper reviews the controversial cytological evidence, hypotheses, and ideas on how the first contact between homologous chromosomes comes about.Key words: synapsis, meiosis, presynaptic alignment, homologous recognition, synaptonemal complex, chromosome pairing.
Promotion of homoeologous chromosome pairing in hybrids of Triticum aestivum × Aegilops variabilis
Authors: Farooq S. , Iqbal N. , Shah T. M.
Published: April 2011

Intergeneric hybrids of Triticum aestivum variety Lu-26 and ph1b mutant of the cultivar Chinese Spring were produced with three accessions, A, B, and E, of Aegilops variabilis. Significant differences were found in the amount of homoeologous chromosome pairing at meiotic metaphase I. Hybrids between wheat variety Lu-26 and accessions A and B of Ae. variabilis showed very little pairing, as indicated by the chiasma frequency of 1.0 and 1.5 per cell, respectively. Hybrids between Lu-26 and accession E, on the other hand, showed significantly increased homoeologous pairing (mean chiasma frequency, 12.6/cell). The level of such pairing was essentially the same as that between the hybrids of ph1b 'Chinese Spring' × Ae. variabilis accessions A and B. However, when the ph1b mutant was hyridized with accession E, the level of chromosome pairing increased significantly (mean chiasma frequency, 17.52/cell). This is indicative of the presence of pairing promoter gene(s) in Ae. variabilis accession E, which are epistatic to the wheat Ph1 allele and positively interact with its mutant form to further increase the ph1b ceiling to homoeologous pairing in wheat.Key words: Triticum aestivum, ph1b mutant, Aegilops variabilis, intergeneric hybrids, homoeologous pairing.
Identification of a family of repeated sequences on the rye B chromosome
Authors: Sandery Michael J. , Forster John W. , Blunden Richard , Jones R. Neil
Published: April 2011

A novel family of highly repeated sequences on the B chromosome of rye (Secale cereale) has been identified. The D1100 family has not been detected on the rye A chromosomes and shows little or no homology to any previously described repeat sequence in rye. In addition, different rye species, and different B chromosomes within the same species, show significant heterogeneity in the arrangement of the D1100 sequences. An EcoRI clone of a member of the family has been obtained. These results provide direct evidence for the organisation and nature of the B-chromosome DNA in rye, and they are discussed in relation to the origin and evolution of rye B chromosomes.Key words: B chromosome, Secale cereale, repeated sequences.
Meiotic pairing control in wheat–rye hybrids. I. Effect of different wheat chromosome arms of homoeologous groups 3 and 5
Authors: Cuadrado C. , Romero C. , Lacadena J. R.
Published: April 2011

Wheat–rye hybrids were analyzed to study how the homoeologous-pairing control of wheat is altered when specific regulators of groups 3 and 5 are lacking or mutated. Lack of the 3DS chromosome arm and the ph2b mutation showed the most significant effect, due to a deficiency or inactivity of the Ph2 suppressor. The 3DL, 5AS, and 5BS chromosome arms have a promoting effect, 5BS being the most effective. A weak suppressive effect of 3AS and 3AL is proposed, and a promotive effect of 5DS was not ruled out. The suppressive effect of 3BS is discussed.Key words: Triticum aestivum, Secale cereale, homoeologous chromosomes, genetic pairing regulation.
The R173 family of rye-specific repetitive DNA sequences: a structural analysis
Authors: Rogowsky Peter M. , Manning Susanne , Liu Jin-Yuan , Langridge Peter
Published: April 2011

In contrast to all other characterised families, repetitive DNA sequences of the rye-specific R173 family occur generally as a monomer and have an unusually long repeat unit. A genomic library was generated from a wheat line with three copies of the short arm of chromosome 1 of rye, 1RS. Seventy-seven λ clones, representing independent members of the family, were isolated by hybridization to pAW173. They share a common region of approximately 3.5 kbp, which is free of large internal repeats and therefore constitutes the basic unit of the dispersed R173 family. The analysis of flanking regions showed that individual members of the R173 family are generally not found in the vicinity of other characterised families of repetitive DNA. The flanking regions of four selected λ clones were different from each other and comprised both repetitive and low-copy sequences. A restriction fragment length polymorphism probe, mapping to the short arm of chromosome 1, was obtained by subcloning of flanking regions of the R173 family.Key words: repetitive DNA sequences, wheat, rye, restriction fragment length polymorphism marker.
Duplication of the structural gene for the plastid-specific isozyme of aldolase in Cicer
Authors: Gaur P. M. , Slinkard A. E.
Published: April 2011

Fructose-bisphosphate aldolase (ALD, EC 4.1.2.13) was analysed in Cicer arietinum L. (the cultivated chickpea) and all eight annual wild Cicer species, C. bijugum Rech., C. chorassanicum (Bge.) M. Pop., C. cuneatum Rich., C. echinospermum Davis, C. judaicum Boiss., C. pinnatifidum J. &S., C. reticulatum Lad., and C. yamashitae Kit. Duplicate genes were identified for the plastid-specific isozyme of ALD in C. arietinum and all wild species except C. yamashitae and one accession of C. reticulatum. Gene duplication was indicated by the presence of a true-breeding five-banded zymotype of the tetrameric plastid ALD in these species. Monogenic inheritance was confirmed for the alleles of one of the loci. The occurrence of ALD gene duplication in most of the annual Cicer species suggests that this duplication is of ancient origin. However, this duplication must have occurred after divergence of Cicer from the closely related genera Pisum and Lens because the plastid ALD is controlled monogenically in these latter two genera.Key words: Cicer, isozymes, aldolase, gene duplication.
Population differences in antifreeze protein gene copy number and arrangement in winter flounder
Authors: Hayes Pliny H. , Davies Peter L. , Fletcher Garth L.
Published: April 2011

Many marine fish in polar waters produce antifreeze proteins (AFPs) to depress their serum freezing point to below that of seawater. Winter flounder from the east coast of North America contain multiple AFP gene copies organized both as tandem repeats and as linked but irregularly spaced genes, with the tandemly repeated genes encoding the bulk of the circulating AFPs. We report here on AFP gene organization in winter flounder from nine locations ranging from Long Island, NY to Conception Bay, Nfld. There are clear differences in AFP gene copy number and arrangement between some of the populations. The greatest variation is seen in the size of the tandem component in fish from the warmer, deeper locations. This contrasts to the conservation of organization in the dispersed, β-tubulin multigene family used for comparative purposes. We suggest that variation in AFP gene family size and organization reflects a relaxation of selection in some geographical areas in the postglacial period.Key words: gene dosage, multigene family, tandem repeats, intrapopulation variation, glaciation.
Use of Ipomoea trifida (HBK.) G. Don germ plasm for sweet-potato improvement. 2. Fertility of synthetic hexaploids and triploids with 2n gametes of I. trifida, and their interspecific crossability with sweet potato
Authors: Freyre Rosanna , Iwanaga Masaru , Orjeda Gisella
Published: April 2011

Twenty-two synthetic hexaploids and 33 triploids with 2n pollen production of Ipomoea trifida were used in crosses to estimate their male and female fertility and their crossability with sweet potato, Ipomoea batatas (L.) Lam. Several important conclusions were drawn. (i) The fertility of pollen of the triploid plants was confirmed, which suggested they are truly functional 2n pollen. (ii) The average male fertility of hexaploid plants was higher than that of triploid with 2n pollen production plants. (iii) 2n egg production was observed in several triploid genotypes, (iv) From a polycross, 3079 seeds with normal shapes were produced. These represent a population of hexaploid I. trifida with a wide genetic base, and they may be important material for sweet-potato improvement, (v) A total of 3275 seeds were obtained from crosses with six sweet-potato female parents, of which only 60 germinated, indicating the existence of an interspecific barrier. The implications of 2n gametes for breeding and evolution of sweet potato are also discussed.Key words: Ipomoea batatas, Ipomoea trifida, 2n gametes, sexual polyploidization, triploid.
Possible repetitive DNA markers for Eusorghum and Parasorghum and their potential use in examining phylogenetic hypotheses on the origin of Sorghum species
Authors: Hoang-Tang  , Dube Shyam K. , Liang George H. , Kung Shain-Dow
Published: April 2011

Genomic structures of two major species in section Eusorghum (Sorghum), Sorghum bicolor and Sorghum halepense, and their phylogenetic relationships with a species in section Parasorghum, Sorghum versicolor, were studied by using cloned repetitive DNA sequences from the three species. Of the five repetitive DNA clones isolated from S. bicolor and S. halepense, four produced qualitatively similar hybridization patterns with detectable variations in copy numbers of some of the restriction fragments on the Southern blots of the two genomic DNAs. One clone was shown to be diagnostic for S. halepense. Molecular analysis at the DNA level indicates that S. bicolor and S. halepense have similar but not identical genomes, consonant with differences in karyotypes, meiotic chromosome behaviors, morphology, and physiology of the species. In addition to five repetitive clones isolated from S. bicolor and S. halepense, eight more sequences were cloned from S. versicolor. Nine clones were found to be specific for either S. bicolor and S. halepense or S. versicolor. The remaining four had a moderate to strong homology with sequences present in all Sorghum species studied. We speculate that the genome in the common ancestor of Sorghum has differentiated to give rise to genomes of at least three major chromosome sizes; large, medium, and small, as seen at present. Amplifications, eliminations, rearrangements, and new syntheses of repetitive sequences may have been involved in genome differentiation of these species. The results also suggest that the S. versicolor genome has strongly diverged from the genomes of the two species in section Eusorghum.Key words: repetitive DNA, genome, phylogeny, Eusorghum, Parasorghum, Sorghum.
Changes in the fertility and meiotic behaviour of barley (Hordeum vulgare) × wheat (Triticum aestivum) hybrids regenerated from tissue cultures
Authors: Molnár-Láng M. , Galiba G. , Kovács G. , Sutka J.
Published: April 2011

A total of 41 regenerant plants were raised from two consecutive in vitro propagation cycles from a barley (Hordeum vulgare L. cv. Martonvásári 50) × wheat (Triticum aestivum L. cv. Chinese Spring) hybrid. The second-cycle regenerants exhibited great variability for most morphological traits. The female fertility of certain regenerant hybrids considerably exceeded that of the initial hybrid, giving substantially higher seed set when pollinated with wheat. This character was transferred to the BC1 and BC2 progeny produced from the regenerants. The cytological analysis of the second-cycle regenerants indicated that these had a higher degree of meiotic instability than the initial hybrid. The proportion of cells with 28 chromosomes (21 wheat + 7 barley) dropped to one-half of that in the initial hybrid, with a rise in the number of hypoploid and hyperploid cells. The number of chiasmata per cell increased from 1.7 in the initial hybrid to 4.7 in the regenerants, and there was also an increase in the number of misdivisions.Key words: intergeneric hybrid, tissue culture, fertility, meiotic behaviour, somaclonal variation.
Identification and frequency of tetraploid progeny from 2x–4x and 4x–2x crosses in Dactylis
Authors: Santen Edzard van , Hugessen P. M. , Casler M. D.
Published: April 2011

The utilization of diploid germ plasm in the improvement of tetraploid orchard grass (Dactylis glomerata L. ssp. glomerata Hayek) requires some means of polyploidization. Studies in several different crop species have shown that sexual polyploidization has the advantage of transmitting a large proportion of heterozygosity from the parent to the offspring. In tetrasomic tetraploids, maximum heterozygosity is a necessary requirement for maximum heterosis. The objective of this research was to investigate the occurrence of 2n eggs and 2n pollen in several sources of wild diploid germ plasm, by quantifying the frequency of 4x genotypes among the progeny of interploidy crosses. Pollen diameter was determined in 110 diploid genotypes. These genotypes were then ranked for five descriptive statistics based on diameter (maximum, 75th percentile, median, arithmetic mean, mode). The eight top-ranking genotypes in four of the five categories were crossed to male-sterile 4x seed parents. Randomly selected diploid genotypes were also crossed as seed parents to 4x genotypes. Tetraploid progeny were recovered from both types of crosses. Of 57 2x genotypes, 15 produced 2n eggs. Of the 8 large pollen diameter genotypes, 6 produced 4x progeny in relative frequencies of 3–100%. The success of recovery was dependent on the genotype of the pollen parent as well as the seed parent. Of the 6 genotypes producing 2n pollen, 2 also produced 2n eggs, resulting in the recovery of tetraploids from selfed progeny.Key words: germ-plasm utilization, interploidy crosses, forage grasses, plant introductions.
In situ hybridization to plant telomeres using synthetic oligomers
Authors: Schwarzacher Trude , Heslop-Harrison J. S.
Published: April 2011

The distribution of telomeric repeats in Hordeum vulgare (barley) and Secale cereale (rye) was studied by DNA–DNA in situ hybridization to root-tip chromosome preparations. Biotinylated synthetic oligomers, (TTTAGGG)6 and (CCCTAAA)6, homologous to the consensus sequence of the Arabidopsis thaliana telomeric repeat, were used as probes, and hybridization sites were detected by Texas red fluorescence or horseradish peroxidase catalyzed precipitation of diaminobenzidine. After examination in the light microscope, the same preparations were transferred to the electron microscope for high-resolution analysis. Sites of hybridization were visualized as single or double dots at the end of most chromosome arms. The sizes of the signal dots varied widely, indicating that individual telomeres may contain different numbers of repeats of the telomeric sequence. In contrast to many mammals, no telomere repeats were detected other than at the ends of the chromosomes. At interphase, signals were concentrated in one region of the nucleus, as would be expected from the Rabl orientation typical for dividing cells from cereal root tips.Key words: barley, rye, nuclear architecture, DNA–DNA in situ hybridization, telomeres.
Variation at RFLP loci in Lactuca spp. and origin of cultivated lettuce (L. sativa)
Authors: Kesseli Rick , Ochoa Oswaldo , Michelmore Richard
Published: April 2011

We have examined 67 accessions of Lactuca sativa L. and five related species for variation at restriction fragment length polymorphism loci. Fifty-five clones were used to probe genomic DNA digested separately with three restriction endonucleases; this defined 143 loci. Variation in L. sativa was sampled in detail. Lactuca sativa is closely related to L. serriola but not to any of the other species in this survey: L. saligna, L. virosa, L. perennis, and L. indica. However, Lactuca sativa is not a direct extraction from the sampled populations of L. serriola; other L. serriola populations or some other unknown entities were involved in the evolution of cultivated lettuce. Numerous genetic differences characterized each cultivated type, suggesting a polyphyletic origin for L. sativa.Key words: Lactuca sativa, lettuce, genetic variation, phylogeny, restriction fragment length polymorphism.
Construction of a restriction fragment length polymorphism map for barley (Hordeum vulgare)
Authors: Heun M. , Kennedy A. E. , Anderson J. A. , Lapitan N. L. V. , Sorrells M. E. , Tanksley S. D.
Published: April 2011

A restriction fragment length polymorphism (RFLP) map for barley (Hordeum vulgare L.) has been developed on the basis of a population of anther culture derived, doubled haploids from the F1 of cultivars 'Proctor' × 'Nudinka'. Wheat genomic, oat cDNA, and barley cDNA clones provided the major source of the probes. Additional clones included genomic clones from Aegilops squarrosa L. and barley, two dehydrin genes, a barley promoter, and a wheat ribosomal gene. In total, 155 RFLPs and two known genes (hulless and Mla12 powdery mildew resistance) have been placed on the linkage map. Clones were assigned to chromosomes using disomic wheat–barley chromosome addition lines. Chromosome arm orientation was done using 'Chinese Spring' wheat nullisomic–tetrasomic and ditelosomic aneuploid stocks. Markers have been located on all chromosome arms except 6S, and the total map length is 1096 centimorgans (cM). Considerations involved in RFLP mapping, including choice and number of restriction endonucleases, disturbed segregation ratios, and uneven distribution of markers in the genome are discussed as well as future improvements and applications of this map.Key words: restriction fragment length polymorphism, mapping, Hordeum vulgare L., Mla12.