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Biomedical subjects

B S Gill

Publications and source records attributed to B S Gill.

At least 37 records · Page 2Linked to original sources
PubMed2003

Mapping of a resistance gene effective against Karnal bunt pathogen of wheat.

A set of 130 wheat recombinant inbred lines (RILs) developed from a cross between parents susceptible (WL711) and resistant (HD29) to Karnal bunt (caused by Tilletia indica), were screened for 3 years with the pathogen populations prevalent in northern India. When 90 simple sequence repeats (SSRs) and 81 amplified fragment length polymorphism (AFLP) loci were mapped on the RILs, markers on chromosomes 2A, 4B and 7B accounted collectively for about one-third of the variation in the disease reaction. The genomic region of largest effect, identified on the long arm of chromosome 4B, reduced Karnal bunt disease by half in three different experiments and accounted for up to 25% of the phenotypic variation for KB reaction. A closely linked SSR marker, GWM538, may be useful in marker-assisted selection for Karnal bunt resistance in wheat.

Chromosome Mapping↗
PubMed2002

A strategy for enhancing recombination in proximal regions of chromosomes.

As a rule, recombination in bread wheat (Triticum aestivum L.) is low in proximal and high in distal regions of chromosomes. Recombination may be enhanced in proximal regions by using deletion (del) chromosomes deficient for a distal part of a chromosome arm. The chromosome del5BL-11 derived from Chinese Spring (CS) is missing 41% of the distal long arm. This line was made polymorphic by crossing with a stock in which chromosome 5B of CS (5B(CS)) is substituted for chromosome 5B of T. turgidum ssp. dicoccoides origin (5B(T.dic)). Three recombinant del5BL-11 (del5BL-11(rec)) lines were isolated, all resulting from localized recombination between loci Xbcd926 and XksuH1. In del5BL-11(rec), the centromere to fraction length (FL) 0.53 (C-FL0.53) segment is derived from 5B(T. dic) and the distal region of FL 0.55-0.59 is from 5B(CS). Genetic recombination for the C-FL 0.53 interval was assayed in segregating progenies from 5B(CS)/5B(T.dic) and del5BL-11/del5BL-11(rec) crosses using polymorphic markers and for the FL 0.55-0.59 interval in del5BL-11/del5BL-11(rec) cross from chiasma counts. The pairing data and comparative mapping of normal 5B and del5BL-11 indicated that the increase in recombination was restricted to the FL 0.55-0.59 interval of the del5BL-11 chromosome. No significant increase in recombination in more proximal regions was observed although the order of several markers that cosegregated in the normal 5B map was resolved in the del5BL-11 map. The presented data show that recombination in proximal, usually low-recombination, regions can be increased by placing them close to the chromosome end.

Centromere↗
PubMed2001

The centromere structure in Robertsonian wheat-rye translocation chromosomes indicates that centric breakage-fusion can occur at different positions within the primary constriction.

Univalent chromosomes at meiotic metaphase I have a tendency to misdivide at the centromeres. Fusion of the misdivision products may produce Robertsonian translocations. The fine structure of the centromeres in Robertsonian wheat-rye translocation chromosomes was analyzed by fluorescence in situ hybridization (FISH) using two centromere-specific DNA clones: pRCS1, derived from rice, and pAWRC1, derived from rye. Clone pRCS1 hybridizes to the centromeres of all grasses including wheat and rye, whereas clone pAWRC1 is rye specific and hybridizes only to the centromeres of rye. Four of the six wheat-rye translocations derived from a single centric misdivision event (1st generation translocations) had hybrid centromeres, with approximately half of the centromere derived from rye and half from wheat. In the two other 1st generation translocations, the entire centromere was derived from rye. Among eight reconstructed wheat and rye chromosomes that originated from two consecutive centric misdivision-fusion events (2nd generation translocations), T1BS.1BL (derived from T1BS.1RL and T1RS.1BL) and one of three T2BS.2BL (derived from T2RS.2BL and T2BS.2RL) had hybrid centromeres. T1RS.1RL (derived from T1BS.1RL and T1RS.1BL), two of three T2BS.2BL, and all three T2RS.2RL (derived from T2RS.2BL and T2BS.2RL) had rye centromeres. All three 3rd generation translocations had hybrid centromeres with approximately half of the centromere derived from rye. There were no indications that the composite structure of the centromere in these chromosomes affected their behavior in mitosis or meiosis. These observations support the notion of a compound structure of the centromere in higher organisms, and indicate that during the centric breakage-fusion event, centromere breakage may occur in different positions along the segment of the chromosome that interacts with the spindle fibers. Normal behavior of the 1st, 2nd, and 3rd generation centric translocations in mitosis and meiosis indicates that, at least in wheat and rye, centromeres are not chromosome specific.

Cell Line↗
PubMed2001

Chromosome healing by addition of telomeric repeats in wheat occurs during the first mitotic divisions of the sporophyte and is a gradual process.

Alien gametocidal chromosomes cause extensive chromosome breakage prior to S-phase in the first mitotic division of gametophytes lacking the alien chromosome. The broken chromosomes may be healed either by addition of telomeric repeats in the gametophyte or undergo fusions to form dicentric or translocation chromosomes. We show that dicentric chromosomes undergo breakage fusion-bridge (BFB) cycles in the first few mitotic divisions of the sporophyte, are partially healed before the germ line differentiation regimen, and are healed completely in the ensuing gametophytic stage. The gametocidal factor on chromosome 4Mg of Aegilops geniculata was used to induce dicentrics involving the satellite chromosomes1B and 6B of wheat, Triticum aestivum. The dicentrics 1BS x 1BL-2AL x 2AS and 6BS x 6BL-4BL x 4BS initiated BFB cycles that ceased 2 to 4 weeks after seed germination. At the end of the BFB cycles, we observed deficient 1B and 6B chromosomes with breakpoints in proximal regions of the 1BL and 6BL arms. The process of chromosome healing was analyzed in root tip meristems, at meiotic metaphase I, and in the derived progenies by fluorescence in-situ hybridization analysis using a telomeric probe pAtT4. The results show that chromosome healing in wheat occurs during very early mitotic divisions in the sporophyte by de-novo addition of telomeric repeats and is a gradual process. Broken chromosome ends have to pass through several cell divisions in the sporophyte to acquire the full telomeric repeat length.

Cell Differentiation↗
PubMed2001

The role of surgery in children with neurofibromatosis.

BACKGROUND/PURPOSE: Neurofibromatosis frequently is complicated by the development of symptomatic lesions such as optic gliomas and plexiform neurofibromas that require operative resection. Although characteristically benign, these neoplasms have often devastating functional and cosmetic effects and must be monitored for malignant transformation. The purpose of this study is to identify and describe the surgical considerations in the care of children with neurofibromatosis. METHODS: The authors reviewed the charts of all children (<21) at our institution with neurofibromatosis who underwent an operative procedure from 1979 to 1999. Patient demographics, symptomatic lesions, malignant transformation, form of surgical intervention, type of anesthesia, and outcome were collected. RESULTS: A total of 249 patients with either neurofibromatosis 1 or 2 were identified. Of these, 50 (20%) underwent a total of 93 operations. The average age at operation was 9.4 years (1.2 to 21 years). There were 40 soft tissue procedures, 21 intracranial, and 32 miscellaneous. The soft tissue masses typically were treated with wide local excision, and in 8 of these procedures multiple resections were performed. Fourteen of the 50 patients had malignancies. Five of the tumors were soft tissue sarcomas, and 9 were intracranial malignancies. Three patients died, 2 from malignancy and 1 from acute, obstructive hydrocephalus after operation. There were 3 patients alive with malignancy and 8 others living with varying levels of disability. CONCLUSIONS: Neurofibromatosis in the pediatric patient frequently requires surgical intervention, often because of symptoms such as pain or cosmetic deformity, or for malignancy. Children should be watched carefully for signs of malignant transformation and undergo biopsy for neurofibromas that exhibit rapid growth. Management of sarcomas should be aggressive with consideration given to re-excision, placement of brachytherapy catheters, metastectomy, and limb salvage with adjuvant therapy when possible. Preoperatively, children should receive clinical and radiographic (computed tomography or magnetic resonance imaging) evaluation for hydrocephalus.

Adolescent↗
PubMed2001

Patient evaluation and management with selective use of magnetic resonance cholangiography and endoscopic retrograde cholangiopancreatography before laparoscopic cholecystectomy.

OBJECTIVE: To assess the utility of triage guidelines for patients with cholelithiasis and suspected choledocholithiasis, incorporating selective use of magnetic resonance cholangiography (MRC) and endoscopic retrograde cholangiopancreatography (ERCP) before laparoscopic cholecystectomy (LC). SUMMARY BACKGROUND DATA: ERCP is the most frequently used modality for the diagnosis and resolution of choledocholithiasis before LC. MRC has recently emerged as an accurate, noninvasive modality for the detection of choledocholithiasis. However, useful strategies for implementing this diagnostic modality for patient evaluation before LC have not been investigated. METHODS: During a 16-month period, the authors prospectively evaluated all patients before LC using triage guidelines incorporating patient information obtained from clinical evaluation, serum chemistry analysis, and abdominal ultrasonography. Patients were then assigned to one of four groups based on the level of suspicion for choledocholithiasis (group I, extremely high; group 2, high; group 3, moderate; group 4, low). Group 1 patients underwent ERCP and clearance of common bile duct stones; group 2 patients underwent MRC; group 3 patients underwent LC with intraoperative cholangiography; and group 4 patients underwent LC without intraoperative cholangiography. RESULTS: Choledocholithiasis was detected in 43 of 440 patients (9.8%). The occurrence of choledocholithiasis among patients in the four groups were 92.6% (25/27), 32.4% (12/37), 3.8% (2/52), and 0.9% (3/324) for groups 1, 2, 3, and 4, respectively (P <.001). MRC was used for 8.4% (37/440) of patients. Patient triage resulted in the identification of common bile duct stones during preoperative ERCP in 92.3% (36/39) of the patients. Unsuspected common bile duct stones occurred in six patients (1.4%). CONCLUSIONS: The probability of choledocholithiasis can be accurately assessed based on information obtained during the initial noninvasive evaluation. Stratification of risks for choledocholithiasis facilitates patient management with the most appropriate diagnostic studies and interventions, thereby improving patient care and resource utilization.

Algorithms↗
PubMed2001

[RFLP analysis of wheat-L. racemosus translocation lines].

A number of wheat-L. racemosus translocation lines were developed by irradiation, pollen culture and gametocidal chromosome methods. In order to identify homozygous translocation lines and determine the exact location of the breakpoints involved in the translocations, 67 probes genetically or physically mapped previously on wheat chromosomes belonging to seven homoeologous groups were used for RFLP analysis. Three homozygous translocation lines were identified: T1BL.7Lr # 1S, T4BS.4BL-7Lr # 1 and T6AL.7Lr # 1S. In lines T1BL.7Lr # 1S and T6AL.7Lr # 1S, the breakpoint of chromosome 7Lr # 1 was located in the short arm between the area marked by clone MWG808 and that of ABG476.1, and the breakpoints of chromosomes 1B and 6A were both located near the centromere. In line T4BS.4BL-7Lr # 1S, the breakpoint of chromosome 7Lr # 1 was located in the short arm between the area marked by clone BCD349 and that of CDO595, the breakpoint of chromosome 4B was located in the long arm between the area marked by clone CDO541 and that of PSR164.

Polymorphism, Restriction Fragment Length↗
PubMed2000

Recombination in an isochromosome preferentially occurs between cis isochromatids.

An isochromosome has identical arms attached to the same centromere. At the pachytene stage of meiosis, it has four isochromatids and recombination can occur either between cis isochromatids (attached to the same half-centromere) or trans isochromatids (attached to different half-centromeres). Normally such recombination cannot be detected because all four chromatids are homogenetic (arose from misdivision of a centromere to which genetically identical sister chromatids were attached). We isolated an isochromosome of wheat that is heterogenetic for the distal 64% of the long arm. The heterogenetic isochromosome was recovered from the progeny of a cross between Triticum aestivum cv. Chinese Spring containing an isochromosome for the long arm of chromosome 5B (i5BL) and a disomic substitution line of Triticum turgidum ssp. dicoccoides chromosome 5B in Chinese Spring wheat. New recombinants were produced when the two arms of i5BLrec paired at metaphase I of meiosis. Only trans isochromatid exchanges led to some homozygous loci in i5BLrec, whereas exchanges between cis isochromatids resulted in heterozygosity at all loci similar to the parental type. There was an average frequency of 0.87 chiasmata per pollen mother cell for the heterogenetic i5BL, which will result in 0.44 cis and 0.44 trans isochromatid exchanges, assuming that both are occurring at the same frequency. The average crossover frequency based on recombination between trans isochromatid exchange detected by restriction fragment length polymorphism analysis in 98 plants was 0.29. This observed value is significantly lower (P<0.01) than the value of 0.44 as expected from chiasmata counts. Our study provides the first experimental evidence that crossovers preferentially occur between cis isochromatids rather than trans isochromatids.

Chromatids↗
PubMed2000

Gametocidal factor-induced structural rearrangements in rye chromosomes added to common wheat.

The gametocidal factor on the Aegilops cylindrica chromosome 2Cc was used to induce and analyze the nature of chromosomal rearrangements in rye chromosomes added to wheat. For this purpose we isolated plants disomic for a given rye chromosome and monosomic for 2Cc and analyzed their progenies cytologically. Rearranged rye chromosomes were identified in 7% of the progenies and consisted of rye deficiencies (4.6%), wheat rye dicentric and rye ring chromosomes (1.8%), and terminal translocations (0.6%). The dicentric and ring chromosomes initiated breakage-fusion-bridge cycles (BFB) that ceased within a few weeks after germination as the result of chromosome healing. Of 56 rye deficiencies identified, after backcrossing and selfing, only 33 were recovered in either homozygous or heterozygous condition covering all rye chromosomes except 7R. The low recovery rate is probably caused by the presence of multiple rearrangements induced in the wheat genome that resulted in poor plant vigor and seed set, low transmission, and an underestimation of the frequency of wheat rye dicentric chromosomes. Genomic in-situ hybridization (GISH) analysis of the 33 recovered rye deficiencies revealed that 30 resulted from a single break in one chromosome arm followed by the loss of the segment distal to the breakpoint. Only three had a wheat segment attached distal to the breakpoint. Although some of the Gc-induced rye rearrangements were derived from BFB cycles, all of the recovered rye rearrangements were simple in structure. The healing of the broken chromosome ends was achieved either by the de-novo addition of telomeric repeats leading to deficiencies and telocentric chromosomes or by the fusion with other broken ends in the form of stable monocentric terminal translocation chromosomes.

Chromosomes↗
PubMed2000

Fate of multicentric and ring chromosomes induced by a new gametocidal factor located on chromosome 4Mg of Aegilops geniculata.

A new gametocidal (Gc) factor was identified on chromosome 4Mg of Aegilops geniculata Roth. When transferred to Chinese Spring wheat, monosomic and disomic Triticum aestivum-Ae. geniculata chromosome 4Mg addition plants undergo regular first and second meiotic divisions. Male gametogenesis in disomic 4Mg addition plants also is normal. However, chromosome breakage and anaphase bridges were observed at ana/telophase of the first (29%) and second (11%) pollen mitosis in monosomic 4Mg addition plants. Gc-induced multicentric and ring chromosomes can be transmitted to the offspring and initiate breakage fusion bridge (BFB) cycles in dividing root tip meristem cells of the derived sporophytes. The fate of multicentric and ring chromosomes was analyzed in root meristems at different time intervals after seed germination. The majority of the BFB cycles ceased about 32 days after germination. Broken chromosome ends were healed either by the fusion of a centric and an acentric fragment forming terminal translocation chromosomes or as deficiencies or telocentric chromosomes. Lack of cytologically detectable telomeric repeats at the stabilized newly broken termini suggests that chromosome healing by addition of telomeric repeats may be a gradual process.

Centromere↗
PubMed2000

Meiotic metaphase I pairing behavior of a 5BL recombinant isochromosome in wheat.

A recombinant isochromosome i5BLrec of wheat was developed with one arm and the proximal 36% of the other arm of Chinese Spring (CS) origin and the distal 64% of the recombined arm of Triticum turgiduM subsp. dicoccoides origin. The i5BLrec provides an unusual opportunity to analyze the role of the centromere or arm heterozygosity in chromosome prealignment and synapsis during meiosis. In monosomic condition, the i5BLrec formed a ring univalent in 86.8% of the pollen mother cells (PMCs) at meiotic metaphase I. In the disomic condition, the two i5BLrec preferentially paired as a normal bivalent in 74.8% of the PMCs, which differed significantly (p <0.01) from the normal bivalent pairing of 51% observed in diisosomic 5BL chromosomes of the CS (Di5BL(CS)) control plants. In plants with one i5BLrec and a normal 5B(CS), the long arm of 5B(CS) paired with the homologous arm of i5BLrec in 54.4% of the PMCs, and 40.4% of the PMCs had a 5B(CS) univalent and a i5BLrec ring univalent. The implications of the i5BLrec pairing data on the mechanism of Ph1 gene action are discussed.

Chromosome Banding↗
PubMed2000

Saturation mapping of a gene-rich recombination hot spot region in wheat.

Physical mapping of wheat chromosomes has revealed small chromosome segments of high gene density and frequent recombination interspersed with relatively large regions of low gene density and infrequent recombination. We constructed a detailed genetic and physical map of one highly recombinant region on the long arm of chromosome 5B. This distally located region accounts for 4% of the physical size of the long arm and at least 30% of the recombination along the entire chromosome. Multiple crossovers occurred within this region, and the degree of recombination is at least 11-fold greater than the genomic average. Characteristics of the region such as gene order and frequency of recombination appear to be conserved throughout the evolution of the Triticeae. The region is more prone to chromosome breakage by gametocidal gene action than gene-poor regions, and evidence for genomic instability was implied by loss of gene collinearity for six loci among the homeologous regions. These data suggest that a unique level of chromatin organization exists within gene-rich recombination hot spots. The many agronomically important genes in this region should be accessible by positional cloning.

Biological Evolution↗
PubMed2000

Physical characterization of the homoeologous group 5 chromosomes of wheat in terms of rice linkage blocks, and physical mapping of some important genes.

The wheat homoeologous Group 5 chromosomes were characterized physically in terms of rice linkage blocks using a deletion mapping approach. All three chromosomes, 5A, 5B, and 5D, were shown to have a similar structure, apart from the 4A-5A translocation on the distal end of chromosome arm 5AL. The physical mapping of rice markers on the deletion lines revealed that the whole of rice chromosome 9 is syntenous to a large block, proximal to the centromere, on the long arm. Likewise, a small segment of the distal end of the long arm showed conserved synteny with the distal one-third end of the long arm of rice chromosome 3. In between those conserved regions, there is a region on the long arm of the Group 5 chromosomes which shows broken synteny. The proximal part of the short arms of the Group 5 chromosomes showed conserved synteny with a segment of the short arm of rice chromosome 11 and the distal ends showed conserved synteny with a segment of rice chromosome 12. The physical locations of flowering time genes (Vrn and earliness per se) and the gene for grain hardness (Ha) on the Group 5 chromosomes were determined. These results indicate that comparative mapping using the deletion mapping approach is useful in the study of genome relationships, the physical location of genes, and can determine the appropriate gene cloning strategy.

Chromosome Mapping↗
PubMed1999

Ultrasonic dissectors and minimally invasive surgery.

As increasingly complex operations are performed laparoscopically, new problems arise regarding basic tasks such as dissection and retraction. Emerging technologies continue to reduce the technical demands of minimally invasive surgery. Recent studies have shown that ultrasonic devices have the potential to replace electrocautery without compromising safety in minimally invasive operations. With the combination of several functions into a single instrument, significant reductions in operative time and expense are possible and should increase the acceptance of this new technology.

Hemostasis, Endoscopic↗
PubMed1999

Molecular cytogenetic analysis of Aegilops cylindrica host.

The genomic constitution of Aegilops cylindrica Host (2n = 4x = 28, DcDcCcCc) was analyzed by C-banding, genomic in situ hybridization (GISH), and fluorescence in situ hybridization (FISH) using the DNA clones pSc119, pAs1, pTa71, and pTA794. The C-banding patterns of the Dc- and Cc-genome chromosomes of Ae. cylindrica are similar to those of D-and C-genome chromosomes of the diploid progenitor species Ae. tauschii Coss. and Ae. caudata L., respectively. These similarities permitted the genome allocation and identification of the homoeologous relationships of the Ae. cylindrica chromosomes. FISH analysis detected one major 18S-5.8S-25S rDNA locus in the short arm of chromosome 1Cc. Minor 18S-5.8S-25S rDNA loci were mapped in the short arms of 5Dc and 5Cc. 5S rDNA loci were identified in the short arm of chromosomes 1Cc, 5Dc, 5Cc, and 1Dc. GISH analysis detected intergenomic translocation in three of the five Ae. cylindrica accessions. The breakpoints in all translocations were non-centromeric with similar-sized segment exchanges.

Chromosome Banding↗
PubMed1998

Plant cytogenetics at the dawn of the 21st century.

The years 1996-1997 saw advances in plant chromosome handling, structure, behaviour and manipulation. Improved protocols were developed for flow sorting, microdissection and microcloning. Fibre FISH was used to map a range of DNA sequences at a resolution of a few kilobases. Over 400 wheat deletion stocks were reported and healing of broken chromosomes by de novo addition of telomeric sequences was demonstrated. Centromeric DNA sequences were identified. The role of telomeric ends in pairing was demonstrated. Apparently unusually long chromosome arms can interfere with mitosis. Novel phenomena and potential of wide hybrids for genome analysis were noteworthy.

Chromosomes↗
PubMed1998

Molecular cytogenetic analysis of tetraploid and hexaploid Aegilops crassa.

The distribution of highly repetitive DNA sequences on chromosomes of tetraploid and hexaploid cytotypes of Aegilops crassa (Dcr1Xcr and Dcr1XcrDcr2 genomes) was studied using C-banding and in situ hybridization analyses with the pSc119, pAs1 and pTa794 DNA clones. In total, 14 tetraploid and five hexaploid accessions were examined. All chromosomes can be identified by their C-banding and ISH pattern with the pAs1 DNA clone. Only a few pSc119 hybridization sites were observed in the telomeric regions of several chromosomes. We found a high level of C-banding polymorphism and only minor variations in labeling patterns. The position of C-bands generally coincided with the location of the pAs1 sequence. Three 5S rDNA loci were detected in tetraploid Ae. crassa, whereas five pTa794 ISH sites were observed in 6x Ae. crassa. All the hexaploid accessions differed from the tetraploids by a reciprocal non-centromeric translocation involving chromosomes A and N. Three additional translocations were detected in the accessions analyzed. The Dcr1 genome of 4x Ae. crassa is highly modified compared with the D genome of the progenitor species Ae. tauschii. Because of the large amount of chromosomal rearrangements, the origin of the Xcr genome remains unknown. The second Dcr2 genome of 6x Ae. crassa is different from the Dcr1 genome but is similar to the D-genome chromosomes of Ae. tauschii, indicating that no additional large rearrangements occurred at the hexaploid level.

Chromosome Banding↗