bluuebunny/crossref_metadata_2025 huggingface dataset:
Synaptonemal complex behavior in asynaptic maize
Authors: Maguire Marjorie P. , Riess Robert W.
Published: April 2011

Synatonemal complexes were studied in silver-stained spread preparations of microsporocyte complements of asynaptic maize. Complexes were found predominantly in terminal regions of chromosome pairs. These tend to be aggregated in a common portion of the nucleus and to have polar orientation. As many as 19 of the 20 ends were found to be involved in relatively short paired segments. Intercalary regions of cores were not strongly organized and aligned, but some contained completed synaptonemal complex segments. The defect in asynaptic appears to represent stalling of the synaptic process at an early stage of synaptic progression.Key words: chromosome pairing, synaptonemal complex, synaptic defect.
C-bands and chiasma distribution in Scilla siberica (Hyacinthaceae)
Authors: Berger R. , Greilhuber J.
Published: April 2011

The distribution of chiasmata and their relationship to heterochromatic segments in Scilla siberica (Hyacinthaceae) have been analyzed in pollen mother cell meiosis by means of a Giemsa C-banding technique. All chromosomes could be identified in the meiotic cells. C-bands have a clear effect on chiasma distribution. Regions adjacent to intercalary homomorphic C-bands showed higher chiasma frequencies than other euchromatic regions. Chiasma distribution in bivalents of chromosome variants without these intercalary C-bands is different from those with C-bands. Strongly heterozygous C-blocks lead to a pronounced reduction of chiasma frequency in their vicinity. Mechanical clues for this are found in pachytene pairing behaviour of heterozygous C-bands, which also indicates that euchromatin is constant and C-bands are variable and additional segments. Within one anther, equational separations of C-band heteromorphisms were less than expected from corresponding metaphase I bonds, presumably because of a lower chiasma frequency in early meiotic cells. Heteromorphic intercalary C-bands show that chiasmata do not terminalize. Only at the onset of anaphase I does chiasma resolution result in transitory configurations reminiscent of terminalization.Key words: Scilla siberica, C-bands, meiotic recombination.
Gliadin gene location and C-banding identification of Aegilops longissima chromosomes added to wheat
Authors: Hueros G. , Gonzalez J. M. , Sanz J. C. , Ferrer E.
Published: April 2011

Gliadin protein components from Aegilops longissima were separated by two-dimensional electrophoresis. No equivalents for α-gliadin were noted. Addition and substitution lines of Ae. longissima in Triticum aestivum 'Chinese Spring' allowed the identification of homoeologous Gli-1 and Gli-2 loci in Ae. longissima chromosomes 1S1 and 6S1. The chromosomal constitution of the alien addition lines was ascertained by C-banding. In addition, C-banding analysis revealed that the Ae. longissima addition set was incomplete as only six distinct addition lines were identified. No evidence for structural modifications between the alien chromosomes in the lines and their Ae. longissima counterparts was found.Key words: gliadins, C-banding, gene location, Aegilops longissima, wheat.
Induction of parthenogenesis, and chromosome behavior in plants of parthenogenetic origin in cotton (Gossypium hirsutum)
Authors: Shi-Qi Zhou , De-Qi Qian , Xiu-Yun Cao
Published: April 2011

Different chemical, physical, and biological treatments were applied to emasculated flower buds of cotton hybrids (Gossypium hirsutum, 2n = 4x = 52) of various genotypes with the purpose of inducing haploid parthenogenesis. Of the treatments applied, the most effective chemical treatment was 0.2% colchicine in 0.2% dimethyl sulfoxide (1.22% parthenogenetic seed set), the most effective physical treatment was high temperature (2.66% parthenogenetic seed set), and the most effective biological treatment was pollination with Hibiscus cannabinus pollen (2.33% parthenogenetic seed set). In the progeny of five plants of parthenogenetic origin, chromosome number and meiotic behavior were studied. All were mixoploids at the dihaploid level and yet set bolls almost like normal allotetraploids. Chromosome numbers ranged from 12 to 56 in the root tips within plants, with a somewhat less pronounced variation between pollen mother cells. At meiotic metaphase I in pollen mother cells 89.8% of the chromosomes were associated. Of the bivalents 23.3% showed AA pairing, 18.7% showed DD pairing, and 18.4% showed AD pairing. Trivalents and higher multivalents involved 29.4% of the chromosomes, and 10.2% were univalents. Anaphase I segregation was often unequal. Yet fertility was as high as in the allotetraploid. It is possible that the second generation was formed by parthenogenesis after restitution in the embryonic mother cells.Key words: Gossypium hirsutum, cotton, parthenogenesis, mixoploidy, meiosis fertility.
Genetic organization of the cSOD microregion of Drosophila melanogaster
Authors: Staveley Brian E. , Hilliker Arthur J. , Phillips John P.
Published: April 2011

Cu/Zn superoxide dismutase (cSOD) is an important enzymatic agent of physiological defense against active oxygen species. Previously, we defined the essential biological role of cSOD in Drosophila through analysis of a cSOD null mutant. In the process of isolating this mutant, we also identified several vital genes in the chromosomal region surrounding the cSOD gene (the cSOD microregion). To further our genetic analysis of cSOD function, we have undertaken a detailed description of the cSOD microregion as defined by the breakpoints of the deficiency Df(3L)lxd9. Examination and correlation of mutations previously recovered with new X-ray induced mutations described in this paper identify a total of 12 vital genes, including cSOD, and one nonvital gene, lxd, in this region. We propose the adoption of a single genetic nomenclature for the genes of this region. Two newly generated hypomorphic alleles of cSOD are described that confer phenotypes similar to cSODn108, confirming the important physiological role of the enzyme in Drosophila.Key words: Cu/Zn superoxide dismutase, oxygen defense.
Restriction fragment analysis of ribosomal and hordein genes in eastern Canadian two-rowed barleys
Authors: Molnar Stephen J. , McKay Adèle
Published: April 2011

Restriction fragment length polymorphisms (RFLPs) have been advocated as useful genetic markers for a variety of genetic and plant breeding applications. Among barley cultivars, RFLPs have been reported in three well-characterized multigene families: at the hordein seed storage protein loci, at the 18S + 5.8S + 26S ribosomal DNA loci, and for 5S ribosomal DNA. The present study sampled RFLPs in these three gene families in the five major eastern Canadian two-rowed barley cultivars. The target sequences constitute at least six loci distributed over at least three chromosomes but represent a very small percentage of the total genome. The five cultivars studied share common alleles at the 18S + 5.8S + 26S ribosomal loci Rrn 1 and Rrn 2 and at the 5S ribosomal loci. This may reflect a fairly narrow genetic base for these cultivars. Moderate amounts of polymorphism were detected at the Hor 1 and Hor 2 loci, each of which comprises a small multigene family. Restriction fragment length polymorphism complemented protein polymorphism at the hordein loci, arguing for their joint use for cultivar identification or similar purposes.Key words: barley, restriction fragment analysis, restriction fragment length, polymorphisms, hordeins, ribosomal DNA.
Heteromorphic sex chromosomes in the Australian frog Crinia bilingua (Anura: Myobatrachidae)
Authors: Mahony M. J.
Published: April 2011

The karyotype of Crinia bilingua was examined and analysed with standard staining, C-banding, and silver-staining. Heteromorphic sex chromosomes of the ZW ♂/ZZ ♀ type were observed. The larger W chromosome is submetacentric and the smaller Z chromosome is acrocentric. The centromere and proximal region of the short arm of the W chromosome consist of constitutive heterochromatin (C-band region), and beyond this is a small euchromatic terminal region. The centromere of the Z chromosome did not C-band. The long arms of the Z and W chromosomes are euchromatic and equal in length. The nucleolar organiser region occurs terminally on the long arm of both the Z and W chromosomes, and there is no cytological evidence for inactivity of the nucleolar organiser region on the W chromosome. These features indicate an early stage in the evolution of heteromorphic sex chromosomes.Key words: heteromorphic sex chromosomes, frog, Crinia bilingua.
Reproductive system and population structure in two Hedysarum subspecies. I. Genetic variation within and between populations
Authors: Baatout Hedi , Combes Daniel , Marrakchi Mohamed
Published: April 2011

Several samples of wild populations of two subspecies of the genus Hedysarum (H. spinosissimum subspecies capitatum, an outcrosser, and H. spinosissimum subspecies euspinosissimum, a selfer) were examined with respect to variability of 25 quantitative characters and allozyme variation at 13 loci. The amount of phenotypic and genetic variation within and among populations was documented. For most of the 25 quantitative characters, the differences between population means and between the total variances of the populations were higher in the selfer than in the outbreeder. Significant among-population genetic variation was found for nearly all characters in the two subspecies, but the outbreeder had higher within-population variability than the selfer with heterogeneity among characters. However, allozyme variation at 13 loci in about the same number of populations showed higher levels of genetic variability in the outcrossing subspecies capitatum compared with the selfing subspecies euspinosissimum, based on measures of mean number of alleles per locus, mean proportion of polymorphic loci, and mean heterozygosity. Therefore, H. spinosissimum subsp. capitatum appeared to be highly polymorphic in contrast to the greater monomorphism within populations of H. spinosissimum subsp. euspinosissimum. The genetic affinities of different populations of a subspecies are uniformly high, with Nei's genetic identity ranging from 0.983 to 0.997 in the selfing subspecies euspinosissimum and from 0.922 to 1.000 in the outcrossing subspecies capitatum.Key words: Hedysarum, genetic variation, populations, electrophoresis.
Independent arrangement of bivalents and (or) quadrivalents in linear meiotic metaphase plates of rye
Authors: Goicoechea P. G. , Roca A. , Linde A. R. , Naranjo T. , Giraldez R.
Published: April 2011

The relative positioning of bivalents and (or) quadrivalents in flattened lateral views of metaphase I (linear metaphase plates) has been analyzed in three different plant types of rye: normal plants (type 1); heterozygotes for translocation T305W (type 2); and double heterozygotes for translocations T305W and TR01 (type 3). In all plant types all bivalents and (or) quadrivalents were identified using C-banding. The results indicate that quadrivalents show a preference towards being located in marginal positions of the linear plate, and there are also differences in position preferences between specific bivalents. Adjacently oriented quadrivalents and rod bivalents show a stronger preference for marginal positions than alternate quadrivalents and ring bivalents, respectively, but this does not indicate the existence of a fixed or ordered arrangement of chromosomes in the spindle since bivalents and (or) quadrivalents are independently located relative to each other.Key words: Secale, meiosis, metaphase, arrangement, multivalents, bivalents.
Association of a nematode resistance bearing addition chromosome with a recurring leaf intumescence somaclonal variation in sugar beet
Authors: Yu M. H. , Pakish L. M. , Saunders J. W.
Published: April 2011

Intumescent leaf variants of sugar beet (Beta vulgaris L.) were obtained through callus culture of a monosomic addition that carried resistance to Heterodera schachtii Schm. The frothy pockmarked appearance of the leaf surface was due to hyperplastic growth of the mesophyll and epidermal cells. The epidermis had many malformed stomata. Veins were underdeveloped, but protrusions beneath were pronounced. Intumescence occurred in 20.3% of the regenerated plants and it was heritable to F1 and later progeny. Leaf intumescence is a new phenotype for Beta. About 73.5% of regenerants contained the donor somatic chromosome number, the remainder were doubled or mixoploids, with no chromosome losses apparent. The 38-chromosome intumescent plant represents a dual somaclonal variation, chromosome doubling and leaf intumescence. Progeny of the 19- and 38-chromosome intumescent plants intercrossed or pollinated by diploids or tetraploids had 9, 18, 19, 27, 28, 29, 36, 37, 38, or 39 chromosomes. All intumescent plants were aneuploids with the monosome addition. There were linkages for leaf intumescence (Li), resistance to H. schachtii (Hs), and hypocotyl color (Rpro) on the addition chromosome. The efficacy of Hs remained intact through the in vitro culture and succeeding crosses. The Li-bearing plants manifested depressed growth and markedly reduced seed set. Leaf intumescence was thought to be the alternative expression of galling potential of Beta procumbens Chr. Sm. germ plasm.Key words: somaclonal variation, leaf intumescence, nematode resistance, monosomic addition, Beta vulgaris L.
Polymorphic minisatellite amplified on avian W chromosome
Authors: Rabenold Patricia P. , Piper Walter H. , Decker Mark D. , Minchella Dennis J.
Published: April 2011

Jeffrey's minisatellite probe 33.15, which screens dozens of hypervariable loci throughout the genome, detects female-specific fragments in stripe-backed wrens (Campylorhynchus nuchalis). HaeIII subdivides the single large female-specific fragment observed with other enzymes into a polymorphic suite of fragments of similar total molecular weight among patterns. Sex-linked HaeIII haplotypes are perfectly transmitted from mother to daughter but not to sons. These results suggest that the female-specific HaeIII fragments represent variable subunits of a single long tandem repetitive array composed of approximately 20-bp repetitive units located outside the pairing region of the W chromosome. That sex-linked fragments do not occur in the congener Campylorhynchus griseus suggests that their entrapment and amplification on the W chromosome in C. nuchalis occurred since the divergence of the two species.Key words: minisatellites, sex chromosome, W chromosome, amplification.
Organization of the 5S ribosomal RNA genes in the genome of tomato
Authors: Lapitan Nora L. V. , Ganal Martin W. , Tanksley Steven D.
Published: April 2011

The 5S ribosomal RNA (rRNA) genes represent one of the most abundant gene families in eukaryotic genomes and have been a model system for the study of molecular organization and evolution of multigene families in eukaryotes. This paper reports a detailed characterization of the 5S rRNA genes of tomato (Lycopersicon esculentum) with respect to chromosome assignment, chromosomal localization, copy number, and physical size. By restriction fragment length polymorphism, the tandemly repeated 5S rRNA genes were assigned to a region of chromosome 1 of tomato. These results were confirmed by in situ hybridization onto tomato metaphase chromosomes. The single hybridization signal was localized to the short arm of chromosome 1, in a region close to the centromere. Based on reconstruction experiments, it was estimated that the 400-bp repeating unit occurs in approximately 1000 copies per haploid genome. Physical characterization of the entire locus was then performed by means of pulsed-field gel electrophoresis. Digestion of high molecular weight DNA of tomato with restriction enzymes such as PvuII, ClaI, and BglII resulted in a very prominent band with a size between approximately 450 and 600 kb. This value closely matched the estimated size of the gene cluster based on reconstruction experiments. The data therefore suggest that all the 5S rRNA genes in tomato occur in a single, continuous array, uninterrupted by unrelated sequences.Key words: 5S rRNA genes, organization, Lycopersicon esculentum, in situ hybridization, pulsed-field gel electrophoresis.
Apomixis in diploid × triploid Tripsacum dactyloides hybrids
Authors: Sherman R. A. , Voigt P. W. , Burson B. L. , Dewald C. L.
Published: April 2011

Apomixis can hinder plant improvement if sexual or apomictic germ plasm of the appropriate ploidy level, required for effective manipulation of apomixis, is not available. To develop needed germ plasm and increase knowledge of apomixis in Tripsacum dactyloides, diploid (2n = 2x = 36) sexual plants were crossed with a highly apomictic triploid (2n = 3x = 54) accession in an attempt to transfer apomixis from a polyploid to the diploid level. The fertility of most hybrids was very low, 69% had 10% or less seed set. A selected subset of 48 hybrids, including most of the more fertile plants, was studied cytologically. The chromosome number of these hybrids ranged from 2n = 36 to 2n = 54. All but 3 of 46 of the 48 hybrids showed indications of apomictic development. Those with near-diploid chromosome numbers were primarily sexual. Highly apomictic hybrids, based on percent diplosporous ovules, had 43 or more chromosomes. Fertility of these hybrids was not related to chromosome number. Fertility of sexual to moderately apomictic plants was reduced as chromosome number increased. Apomixis in T. dactyloides is facultative. Backcrosses are needed to develop germ plasm with a high level of apomixis and near-diploid chromosome numbers.Key words: eastern gama-grass, chromosome number, fertility, mode of reproduction, germ plasm.
Metaphase I pairing of deficient chromosomes and genetic mapping of deficiency breakpoints in common wheat
Authors: Curtis C. A. , Lukaszewski A. J. , Chrzastek M.
Published: April 2011

Metaphase I pairing of deficient chromosomes was analyzed in a set of 'Chinese Spring' (CS) wheat (Triticum aestivum L. em. Thell.) plants with varying lengths of deficiencies in the long arm of chromosome 4A (6, 8, 11, 17, 23, 34, 36, 39, and 50% missing), the long arm of chromosome 5B (49% missing), and the long arm of chromosome 2B (33% missing). Pairing in homologous chromosomes between deficient and complete arms was greatly reduced even by small differences in arm length. In deficiency homozygotes and in an isochromosome derived from a deficient 4AL arm, pairing of the two deficient arms was high and approached that of two complete arms. In plants where deficient and complete arms competed for pairing partners, pairing was exclusively between arms of the same length. These results suggest that in wheat, pairing initiation sites are distributed throughout at least the distal halves of the arms and that the alignment of telomeres may be critical for pairing success. Genetic mapping of the deficiency breakpoints was confounded by misdivision of unpaired chromosomes and abnormal transmission rates. Genetic distances between centromeres and breakpoints appeared to be proportional to metaphase I pairing frequencies.Key words: bread wheat, deficiency, chromosome pairing competition, mapping, telomere, pairing initiation.
Cytogenetic characterization of a genetic sexing strain in Ceratitis capitata
Authors: Zacharopoulou A. , Riva M. E. , Malacrida A. , Gasperi G.
Published: April 2011

A genetic sexing strain of Ceratitis capitata, carrying a null mutation for ADH activity linked to the Y chromosome, was analysed cytogenetically. In addition to an insertion of a large part of the Y chromosome into chromosome 2, this strain carries two other chromosomal rearrangements, a deletion in the second chromosome and a reciprocal translocation involving chromosomes 2 and 4. The progeny of the T(2;4) translocation heterozygote with unbalanced chromosome constitution can survive up to the larval and (or) to the adult stage. These cytological characteristics are discussed in relation to the genetic sexing behaviour of this line.Key words: Ceratitis capitata, polytene chromosomes, genetic sexing.
Bkm satellite DNA and ZFY in the coral reef fish Anthias squamipinnis
Authors: Wachtel Stephen , Demas Suzanne , Tiersch Terrence , Pechan Peter , Shapiro Douglas
Published: April 2011

We studied DNA from the protogynous sex-changing fish Anthias squamipinnis to evaluate the recent observation that male-specific bands are identified after hybridization with Bkm, a probe originating in the W chromosome of the snake Bungarus fasciatus. Sex-specific hybridization would imply modification of DNA structure during the sex-changing process. No sex-specific Bkm fragments were identified in our study, after digestion of DNA from 15 males and 11 adult females, despite the use of 12 different restriction enzymes. However, hybridization with Bkm did produce a distinct fingerprint pattern, similar to the fingerprint patterns described for other species after hybridization with GATA (GACA) type probes. In other experiments, the pDP1007 probe, which identifies the ZFY gene in the male-determining region of the human Y chromosome, generated identical hybridization patterns in DNA from males and females of A. squamipinnis and estimation of DNA mass by flow cytometry revealed identical genome sizes.Key words: Bkm satellite DNA, sex determination, sex change, ZFY, pDP1007, genome size.
Genetic differentiation and inversion clines in Indian natural populations of Drosophila melanogaster
Authors: Das Aparup , Singh B. N.
Published: April 2011

To study the genetic differentiation and inversion clines in Indian natural populations of Drosophila melanogaster, 14 natural populations (6 from the north and 8 from the south) were screened for chromosome inversions. The chromosomal analysis revealed the presence of 23 paracentric inversions, which include 4 common cosmopolitan, 4 rare cosmopolitan, 2 recurrent endemic, and 13 unique endemic (new inversions detected for the first time) inversions. The difference in karyotype frequencies between populations from the north and south were highly significant and the level of inversion heterozygosity was higher in populations from the south. Statistically significant negative correlations were found between each of the four common cosmopolitan inversions and latitude. These findings are in accord with results from other worldwide geographic regions and show that Indian populations of D. melanogaster have undergone considerable genetic differentiation at the level of inversion polymorphism.Key words: Drosophila melanogaster, Indian natural populations, chromosome inversions, genetic differentiation, north–south clines.
A novel Robertsonian translocation in a family of Walker hounds
Authors: Stone Diana M. , Mickelsen W. Duane , Jacky Peter B. , Prieur David J.
Published: April 2011

A 5-year-old female Walker hound was presented to the Washington State University Veterinary Teaching Hospital as a result of a narrowing of the vulva, which prevented natural breeding. All other physical and clinical findings were normal. Cytogenetic analysis disclosed a chromosome number of 77, with three metacentric chromosomes comprised of two X chromosomes and a Robertsonian translocation of two acrocentric autosomes, chromosomes 21 and 33. Cytogenetic analysis of two full-sister siblings with histories of absence of estrus disclosed one with the same translocation and one with a normal female chromosome constitution. The propositus was artificially inseminated with semen from a karyotypically normal male Walker hound and gave birth to nine live grossly normal pups, six females and three males. Another female pup was stillborn but was grossly normal. Cytogenetic analysis of the live pups disclosed that four (three males and one female) of the nine had the same translocation in all lymphocytes. The remaining five pups (five females) had normal female chromosome constitutions. The litter size was average for this breed. This is a previously unreported Robertsonian translocation in dogs.Key words: Robertsonian translocation, canine karyotype, Walker hound.
Cloning and characterization of repetitive DNA sequences from genomes of Oryza minuta and Oryza australiensis
Authors: Aswidinnoor H. , Nelson R. J. , Dallas J. F. , McIntyre C. L. , Leung H. , Gustafson J. P.
Published: April 2011

The value of genome-specific repetitive DNA sequences for use as molecular markers in studying genome differentiation was investigated. Five repetitive DNA sequences from wild species of rice were cloned. Four of the clones, pOm1, pOm4, pOmA536, and pOmPB10, were isolated from Oryza minuta accession 101141 (BBCC genomes), and one clone, pOa237, was isolated from Oryza australiensis accession 100882 (EE genome). Southern blot hybridization to different rice genomes showed strong hybridization of all five clones to O. minuta genomic DNA and no cross hybridization to genomic DNA from Oryza sativa (AA genome). The pOm1 and pOmA536 sequences showed cross hybridization only to all of the wild rice species containing the C genome. However, the pOm4, pOmPB10, and pOa237 sequences showed cross hybridization to O. australiensis genomic DNA in addition to showing hybridization to the O. minuta genomic DNA.Key words: rice, genome-specific repetitive sequences, Oryza.
Changes in expression of seed storage protein genes effected by chromosome 1D of wheat
Authors: Bittel Douglas C. , Hueros Gregorio , Jouve Nicolas , Gustafson J. Perry
Published: April 2011

The effect of chromosome 1D of wheat on expression of seed storage protein genes was analyzed using a 1R(1D) substitution line and derivatives of this line that had lost 1R (1D nullisomic). The results of one- and two-dimensional (two pH) electrophoresis suggested that nucleotide sequences located on 1D were involved in induction and suppression of these protein genes and in posttranscriptional modification of polypeptides produced by the seed storage protein genes. The action attributed to 1D appeared to affect only genes located on chromosome 6A.Key words: electrophoresis, gene expression, suppression, Triticum aestivum.
Nucleolus organization and meiotic behaviour of B chromosomes in Hepatica nobilis
Authors: Mabuchi T.
Published: April 2011

The C-banding karyotype of Hepatica nobilis indicates the A chromosome complement and B chromosomes (Bs) to be banded in the terminal regions. The A chromosomes (As) of this species comprise mainly euchromatin (89.7%) and a small amount of heterochromatin (10.3%). Bs of H. nobilis have terminal centromeres at one end and possess small satellites at the other end. Bs cause an increase in the number of nucleoli per cell, with a decrease in the size of each nucleolus. During meiosis, Bs associate as bivalents and multivalents up to pentavalents. These associate loosely with the short arm of satellited chromosome 7 (end to end association) at diakinesis in some pollen mother cells. Bivalent or trivalent Bs associate with a nucleolus at diakinesis. B chromosomes of H. nobilis thus appear to contain nucleolus organizing regions and may have originated from the satellited chromosome 7 and other members of As.Key words: Hepatica, satellited B, end to end association, origin, nucleolus organizing regions.
Karyological analysis and genome size in Milium (Gramineae) with special reference to polyploidy and chromosomal evolution
Authors: Bennett Simon T. , Thomas Sandra M.
Published: April 2011

Karyotypes, nuclear DNA amounts, and meiotic behaviour are presented for Milium effusum L. (2n = 28), Milium montianum Parl. (2n = 22), and two cytotypes of Milium vernale Bieb. (2n = 8, 10). The bimodal karyotype of M. montianum (8 large and 14 small chromosomes) is described for the first time. Evidence from C-banding and geographical distribution suggests an ancient interracial allopolyploid origin for M. effusum (2n = 28). Although M. montianum is undoubtedly allopolyploid, its parentage is unconfirmed. A strong resemblance between the M. vernale (2n = 8) karyotype and the eight large chromosomes in M. montianum suggests a common ancestry. It is possible that a diploid form of M. effusum contributed the remaining 14 chromosomes. A selective loss of DNA sequences from the smaller chromosomes during the subsequent reorganization of the allopolyploid genome may have enhanced the bimodality of the karyotype. Geographical distribution and a change in the breeding system support the direction of the change x = 5 to x = 4 in M. vernale. Allopolyploidy appears to have played a central role in the chromosome evolution and speciation of Milium.Key words: Milium (Gramineae), karyotype analysis, genome size, polyploidy, chromosome evolution.
The effect of the Ph1 gene in diploid rye, Secale cereale L.
Authors: Schlegel R. , Boerner A. , Thiele V. , Melz G.
Published: April 2011

Experimental results demonstrated clearly that the dominant Ph1 allele of chromosome 5B of wheat affects the homologous pairing of rye chromosomes. A rye-wheat monotelosomic 5BL addition line was produced and used for meiotic studies. Compared with 14-chromosome control plants, the 5BL addition to rye causes an increase in univalents and rod bivalent formation, i.e., a significant reduction of chiasma frequency (11.21 chiasmata per pollen mother cell). The 5BL telosome itself does not associate with any of the rye chromosomes. Thus, the double dosage of 5BL, present in hexaploid or octoploid triticale, could be one of the main causes of pairing failure of the rye genome.Key words: chromosome pairing, Ph1 locus, wheat, rye, rye-wheat addition.
Occurrence and mechanisms of 2n egg formation in 2x potato
Authors: Werner Joanna E. , Peloquin Stanley J.
Published: April 2011

The occurrence of 2n eggs in 381 haploids from six tetraploid parents and in 127 plants representing five diploid wild species was detected using 2x × 4x crosses. Sixty-two percent of the haploids and 24% of the wild-species plants produced 2n eggs. Twenty-six haploids and 17 species plants that gave high seed set in 2x × 4x crosses were examined cytologically to determine the frequency and mechanisms of 2n egg formation. There was significant variation in the frequency of 2n eggs among haploids (7–57%) and among species plants (4.9–57.3%). Five mechanisms of 2n egg formation were identified: synaptic variant (genetically first division restitution); delayed meiotic division (first division restitution and second division restitution); omission of the second division (the prevalent mechanism, second division restitution); irregular anaphase II (second division restitution); and failure of second cytokinesis (second division restitution). 2n eggs can be formed by more than one mechanism within a clone. The occurrence of 2n eggs in wild species and the higher frequency of 2n eggs in haploids than in wild species indicate that sexual polyploidization has been involved in the origin and evolution of polyploid series in potato. The high frequency of 2n eggs in both haploids and diploid wild species allows generation of haploid-species hybrids that produce 2n eggs. These hybrids can then be used in the 2x × 4x and 2x × 2x breeding schemes.Key words: haploids, wild species, 2n gametes, first division restitution, second division restitution.
Variability of C-banding patterns in Japanese quail chromosomes
Authors: Seña C. A. de la , Fechheimer N. S. , Nestor K. E.
Published: April 2011

Observations were made of the C-banding patterns in several cells from 182 Japanese quail embryos to detect presence of stable variants. Each of the eight largest autosomes contains a C-band at the centromeric region. The short arm of autosome 8 is C-band positive, as is the entire W chromosome. The Z chromosome consistently contains an interstitial C-band in the long arm and a less prominent one in the short arm. Distinct variants of chromosome 4 and the Z chromosome were observed. In the Z chromosome a C-band at the terminal region of the short arm was markedly elongated in some embryos. Likewise, the short arm of chromosome 4 was much more prominent in one or both of the homologues in some embryos. Most of the microchromosomes contain a prominent C-band. The heteromorphisms are useful chromosome markers to detect the origins of heteroploidy in early embryos.Key words: C-band variants, Japanese quail, Coturnix.
Organization of a cloned repetitive DNA fragment in mosquito genomes (Diptera: Culicidae)
Authors: Kumar A. , Rai K. S.
Published: April 2011

The structure and genomic organization of a cloned 5.2-kb repetitive DNA fragment, H-85, isolated from the Aedes albopictus genome have been examined. In situ hybridization of the 3H-labeled H-85 DNA to the meiotic and mitotic chromosome preparations of Ae. albopictus shows that the sequences homologous to H-85 DNA are dispersed throughout the length of all three pairs of chromosomes. A similar pattern of in situ hybridization appears in Aedes seatoi, Aedes flavopictus, and Aedes aegypti. The study shows that the arrangement of sequences in the cloned 5.2-kb fragment is rare in the Ae. albopictus genome. Dot-blot hybridization reveals that the sequences homologous to H-85 DNA are present in 12 species of mosquitoes examined, belonging to six genera in subfamilies Culicinae ad Anophelinae. The H-85 sequences are also present in the genome of Mochlonyx velutinus of the nematocerous family Chaoboridae, earlier proposed as the ancestor of the mosquito family Culicidae. Although the sequences homologous to H-85 DNA are present in different species of mosquitoes, they have diverged in their structure and organization. The cloned 5.2-kb fragment is composed of elements of different and independently evolving repetitive DNA families.Key words: repetitive DNA, organization, mosquitoes.
A centromeric satellite DNA in the European plethodontid salamanders (Amphibia, Urodela)
Authors: Batistoni Renata , Nardi Irma , Rebecchi Lorena , Nardone Maria , Demartis Anna
Published: April 2011

A highly repeated satellite DNA (Hy500) located in the centromeric heterochromatin of the European plethodontid salamander Speleomantes (formerly Hydromantes) was studied. The Hy500 family represents about 1% of the Speleomantes supramontis genome and has a major repeating unit of about 500 base pairs, which may have evolved from the progressive amplification of shorter sequences. This centromeric satellite is conserved in all the Speleomantes species, which nevertheless show distinct patterns of chromosomal distribution, which are of relevance as to their phylogenetic relationships.Key words: satellite DNA, amphibian chromosomes.
Sex determination in the dioecious Melandrium album: androgenic embryogenesis requires the presence of the X chromosome
Authors: Veuskens J. , Ye D. , Oliveira M. , Ciupercescu D. D. , Installé P. , Verhoeven H. A. , Negrutiu I.
Published: April 2011

Anther-derived plants of Melandrium album were analysed by flow-cytometric, phenotypic, cytological, and genetic means: more than 90% were classified as females, while no male plants were observed. Instead, one hermaphrodite and several atypical female parental plants were identified. One highly androgenic plant (M5045) turned out to possess two extra autosomes (2n = 26,XY) instead of the ordinary male formula, 2n = 24 (24,XY). The results are discussed in light of possible developmental interactions among the three classes of chromosomes in this dioecious species: male (Y), female (X), and autosomes.Key words: Melandrium album, dioecious, haploids, sex chromosomes, embryogenic development, hormones.
Endosperm mitotic activity and endoreduplication in maize affected by defective kernel mutations
Authors: Kowles R. V. , McMullen M. D. , Yerk G. , Phillips R. L. , Kraemer S. , Srienc F.
Published: April 2011

A group of 35 defective kernel (dek) mutants in maize has been studied with regard to their effect on endosperm development. Information is reported on kernel weight, kernel viability, mutant transmission, DNA content per endosperm nucleus, endosperm cell numbers during development, and DNA endoreduplication patterns. All of the dek mutations reduced mitotic activity and resulted in greatly reduced cell numbers. All except one mutation decreased DNA endoreduplication. The exception indicates that the processes of mitotic activity and endoreduplication can be uncoupled. Notable differences in DNA endoreduplication patterns were observed among the dek strains. Defective kernels with homozygous defective embryos did not germinate in any of these strains, although some morphologically defective kernels did germinate and were shown to have normal embryos of +/+ or +/dek genotype. Dek mutants that had a defective endosperm and an embryo that developed normally were not identified. The mutations investigated are recessive, but F2 segregation for many of the mutants revealed significant deviations from expected 3:1 ratios.Key words: defective kernels, endosperm, endoreduplication.
Scanning electron microscopy of chromosomes of common wheat
Authors: Whelan Ernest D. P. , Kokko E. G.
Published: April 2011

The higher magnifications and resolution possible with scanning electron microscopy can provide more detailed information on chromosome morphology than light microscopy. However, overlying cell debris can obscure surface details. A method is described whereby standard organic acid–alcohol fixatives and slightly modified techniques of routine plant chromosome squash preparations can be used to provide samples of mitotic and meiotic chromosomes of wheat suitable for examination by scanning electron microscopy.Key words: scanning electron microscopy, light microscopy, wheat, chromosomes.
Further hybrids involving the perennial autotetraploid oat Avena macrostachya
Authors: Leggett J. M.
Published: April 2011

Chromosome pairing in the triploid hybrid Avena damascena × A. macrostachya is very similar to the chromosome pairing observed in previously reported triploid hybrids involving the A genome diploid taxa A. atlantica and A. prostrata, indicating that little more than residual homology remains between these A genome diploids and either of the genomes of A. macrostachya. The chromosome pairing in the hybrid between A. macrostachya and the C genome diploid A. ventricosa is similar to that observed in the previously reported hybrid A. eriantha × A. macrostachya. In both these hybrids, the frequency of trivalents is greater than that observed in hybrids involving the A genome species and A. macrostachya, which is indicative of closer homology of A. macrostachya to the C genome diploids than the A genome diploids.Key words: Avena, hybrids, interspecific chromosome pairing, phylogeny.
Fertility and meiotic mechanisms of hybrids between chromosome autoduplication tetraploid wheats and Aegilops species
Authors: Xu Shujun , Dong Yushen
Published: April 2011

During the production of Triticum-Aegilops amphidiploids, it was observed that some F1 hybrids between Triticum ssp. and Aegilops ssp. were self-fertile, with seed set ranging from 0.97 to 39.72%. Seeds from fertile F1's were spontaneous amphidiploids, as determined by root-tip chromosome counts. The present study revealed that the autoduplication of chromosomes in these F1's was caused by the tetraploid wheat parents T. persicum PS5 and T. durum DR147. Detailed meiotic studies of T. persicum PS5 crossed with Ae. squarrosa showed that during meiosis, there were two ways by which unreduced gametes could be formed: first, some of the PMCs omitted the first meiotic division and only underwent the second meiotic division and second, first division restitution with premature cytokinesis, which resulted in an asymmetrical dyad composed of one anucleate cell and one cell with a restitution nucleus. This cell produced two unreduced microspores by a normal second division. The use of this new knowledge has resulted in the production of numerous spontaneous amphiploids of T. persicum crossed with Ae. squarrosa, Ae. speltoides, Ae. umbellulata, Ae. comosa, Ae. ovata, Ae. ventricosa, Ae. crassa, and Ae. triuncialis. Many of these have been produced for the first time.Key words: Triticum, Aegilops, chromosome autoduplication, unreduced gametes, amphidiploids.
Stability at the phosphoglucoisomerase (PGI/2) locus in Lolium multiflorum (2n = 4x = 28) × Festuca arundinacea (2n = 6x = 42) plants regenerated from cell suspension
Authors: Humphreys M. W. , Dalton S. J.
Published: April 2011

Plants were regenerated from a cell suspension from shoot-tip derived callus of a pentaploid Lolium multiflorum (2n = 4x = 28) × Festuca arundinacea (2n = 6x = 42) in which a set of five homologous and homoeologous chromosomes were marked at the PGI/2 locus by distinct alleles. A direct relationship was found in regenerated plants between time in cell suspension and the number of aberrations at the PGI/2 locus. These included deletion of any one, and in a few cases two, of the five PGI/2 alleles, but these were not always related to chromosome loss. In addition three different PGI/2 alleles were each rendered null in some somaclones regenerated last from the cell suspension. While bivalent and trivalent frequency remained unaltered in the regenerated plants compared with the original hybrid, univalent frequency decreased. Chromosome configurations of four or more chromosomes, which probably represent intergeneric chromosome pairing, were significantly increased in the regenerated plants compared with the original hybrid and were negatively correlated with univalents. The possible incorporation of a cell culture phase as a way of increasing intergeneric recombination between L. multiflorum and F. arundinacea chromosomes in a conventional breeding program is discussed.Key words: Festuca–Lolium, somaclonal variation, phosphoglucoisomerase (PGI/2), chromosome instability, somatic recombination.
Chilling injury and chlorotic reactions of euploids and aneuploids of the group 6 homoeologues of common wheat
Authors: Whelan Ernest D. P. , Schaalje G. B.
Published: April 2011

Aneuploid seedlings of the common wheat (Triticum aestivum L.) cv. Chinese Spring (CS) that are nullisomic or telosomic for the long arm of chromosome 6D are susceptible to chilling injury under prolonged exposure to 6 °C; normal euploids or telosomics for the short arm are not. Studies of seedling grown for various durations at 20 °C prior to growth at 6 °C showed that chilling injury was a juvenile phenomenon and that the extent of injury was inversely proportional to the duration of growth at 20 °C to a maximum of about 14 days. When reciprocal crosses were made between susceptible 6D nullisomics or long-arm ditelocentrics of CS and resistant 6D nullisomics of three spring and one winter wheat cultivars, progenies from aneuploid F1 hybrids all segregated for susceptibility as a recessive trait and at a frequency approximating a dihybrid ratio; no cytoplasmic effects were detected. Aneuploids of the group 6 homoeologues of the spring wheat cvs. Cadet and Rescue were resistant, as were group 6 whole-chromosome substitutions of eight different donor wheats in the recipient parent CS and 56 other euploids tested. Genes for resistance to chilling injury appear to involve the group 6 chromosomes and the short arm of 6D in Chinese Spring. In contrast with chilling injury, all aneuploid lines with only four doses of the "corroded" loci on group 6 chromosomes exhibited chlorotic symptoms.Key words: Triticum aestivum, chilling injury.
In situ localization of two repetitive DNA sequences to surface-spread pachytene chromosomes of rye
Authors: Albini S. M. , Schwarzacher T.
Published: April 2011

Surface-spread pollen mother cells at meiotic prophase from Secale cereale (rye) were used for fluorescent DNA:DNA in situ localization of two tandemly repeated DNA sequences: pTa71, a wheat rDNA clone, and pSc119.2, a cloned 120-bp repeat from rye heterochromatin. The fluorescent hybridization signal, consisting of many yellow-green dots, was closely associated with the bivalent axes, corresponding to the synaptonemal complex, and located in the surrounding chromatin. The rDNA signal was associated with one bivalent, the smallest of the seven, at a distance about 13% of the bivalent length from the telomere. This corresponded to the position of the nucleolar organizing region of silver-stained synaptonemal complexes analyzed under the electron microscope and published data for somatic metaphase chromosomes. The relative length of the axis covered with the rDNA signal is less than expected from somatic metaphases, but it corresponds more closely to the proportion of the sequences in the genome. The hybridization signal with the 120-bp repeat was located mainly at the telomeric regions of several bivalents that showed thickenings of the axis after DAPI staining, probably corresponding to somatic C-bands. These major and some minor intercalary sites agree with the distribution of the 120-bp repeat in somatic metaphase. Fluorescent in situ hybridization to plant surface-spread pachytene chromosomes, which can be obtained in large numbers, has great potential for studying meiotic prophase, high-resolution mapping of DNA sequences, and investigating the relationship of DNA sequences to the synaptonemal complex.Key words: in situ hybridization, cereals, pachytene, meiosis, synaptonemal complex, physical mapping.
The genomic inheritance of aluminum tolerance in 'Atlas 66' wheat
Authors: Berzonsky William A.
Published: April 2011

Toxicity to aluminum (Al) limits wheat (Triticum aestivum L. em. Thell.) yields. 'Atlas 66', a soft red winter wheat classified as tolerant (root growth ≥ 0.5 cm after Al stress) to 0.44 mM Al, was hybridized with tetraploid (4x) and hexaploid (6x) 'Canthatch', a hard red spring wheat classified as sensitive (root growth < 0.5 cm after Al stress) to 0.44 mM Al. Progenies produced from these hybridizations were tested for tolerance to 0.44 mM Al in solution to ascertain the number of genes and the genomes of 'Atlas 66', which determine tolerance to aluminum. Tests of 'Atlas 66', 6x-'Canthatch', and the F1's resulting from hybridizations between the parents indicated that dominant, nuclear genes carried by 'Atlas 66' determine tolerance to 0.44 mM Al. Segregation ratios for the F2 significantly differed from ratios expected for a dominant, duplicate genetic mechanism. F1 backcross segregation ratios did not significantly differ from ratios expected for dominant, duplicate nuclear genes for tolerance to aluminum. The expression of genes for tolerance to 0.44 mM Al for 'Atlas 66' appears to be more complex than is predicted by the existence of two dominant genes. A crossing scheme, which involved hybridizing 4x-'Canthatch' with 'Atlas 66', was executed to produce 42-chromosome plants having recombinant A- and B-genome chromosomes and D-genome chromosomes derived exclusively from 'Atlas 66'. Eleven F6 and F7 lines, developed from these plants, were selfed and plants in the F6 generation were backcrossed to 'Atlas 66' and 6x-'Canthatch'. The F6 and F7 lines were subjected to 0.44 mM Al in solution as were the backcrosses. While none of the lines had more than 50% of their seedlings classified as sensitive to Al in the F6 generation, four lines exhibited such a response in the F7 generation. In general, backcrossing the F6 lines to 6x-'Canthatch' increased sensitivity to Al, while backcrossing to 'Atlas 66' increased tolerance. Results suggest that genes for tolerance to Al in 'Atlas 66' wheat are not all located on D-genome chromosomes.Key words: aluminum tolerance, genomic inheritance, Triticum.