The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform
M Schmid - One of the best experts on this subject based on the ideXlab platform.
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Sex chromosome loss and aging: in situ hybridization studies on human interphase nuclei.
American journal of human genetics, 1995Co-Authors: M Guttenbach, B Koschorz, U Bernthaler, T Grimm, M SchmidAbstract:Summary Atotal of1,000 lymphocyte interphase nuclei perprobandfrom90females and138males age1wkto93 years wereanalyzed byinsitu hybridization forloss oftheX andY Chromosomes, respectively. Bothsex Chromosomes showed anage-dependent loss. Inmales, Yhypoploidy wasvery lowuptoage15years (0.05%) butcontinuously increased toafrequency of1.34%in menage76-80years. Infemales, thebaseline level for X chromosome loss ismuchhigher thanthat seenfor theY chromosome inmales. Evenprepubertal females showarateofX chromosome loss, ontheorder of 1.5%-2.5%, rising to-4.5%-5%inwomenolder than75years. Dividing thefemale probands into three biological agegroups onthebasis ofsexhormone function( 51years), asignificant correlation ofX chromosome loss versus age could clearly bedemonstrated inwomenbeyond age51 years. Females age51-91years showed monosomy X atarate from3.2%to5.1%.Incontrast tosexchromosomalloss, thefrequency ofautosomal monosomies doesnotchange during thecourse ofaging: Chromosome1 andchromosome 17monosomic cells were found withaconstant incidence of1.2%and1%,respectively. These data also indicate that autosome loss ininterphase nuclei isnotafunction ofchromosome size.
Mine Arslan-kirchner - One of the best experts on this subject based on the ideXlab platform.
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Chromosome 18 replaced by two ring Chromosomes of chromosome 18 origin.
Human Genetics, 2003Co-Authors: Konstantin Miller, Brigitte Pabst, Joerg Schmidtke, H Ritter, R. Siebert, Peter Nürnberg, Mine Arslan-kirchnerAbstract:We here describe the first example of the replacement of an autosome by two ring Chromosomes originating from the missing chromosome, presented in a patient with a single chromosome 18 and two additional ring Chromosomes. Detailed fluorescence in situ hybridization (FISH) analysis revealed the chromosome 18 origin of both ring Chromosomes and characterized the small and the large ring chromosome as derivatives of the short and long arm of chromosome 18, respectively. The loss of subtelomeric regions of the short and the long arm of chromosome 18 in the ring Chromosomes was confirmed by FISH studies. Molecular studies showed the exclusive presence of the paternal alleles for microsatellite markers located distal to the short and long arm loci D18S843 and D18S474, respectively. This indicates the maternal origin of both rings and provides evidence for substantial deletions of the distal parts of both arms of chromosome 18 in the ring Chromosomes. The dysmorphic features of the patient can be explained by these deletions in both chromosome arms, as the clinical findings partly overlap with observations in 18p- and 18q-syndrome and are similar to some cases of ring chromosome 18. Centromere misdivision is suggested as one mechanism involved in the formation of the ring Chromosomes.
Jiří Král - One of the best experts on this subject based on the ideXlab platform.
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Evolution of multiple sex Chromosomes in the spider genus Malthonica (Araneae: Agelenidae) indicates unique structure of the spider sex chromosome systems
Chromosome Research, 2007Co-Authors: Jiří KrálAbstract:Most spiders exhibit a multiple sex chromosome system, X_1X_20, whose origin has not been satisfactorily explained. Examination of the sex chromosome systems in the spider genus Malthonica (Agelenidae) revealed considerable diversity in sex chromosome constitution within this group. Besides modes X_1X_20 ( M. silvestris ) and X_1X_2X_30 ( M. campestris ), a neo-X_1X_2X_3X_4X_5Y system in M. ferruginea was found. Ultrastructural analysis of spread pachytene spermatocytes revealed that the X_1X_20 and X_1X_2X_30 systems include a pair of homomorphic sex Chromosomes. Multiple X Chromosomes and the pair exhibit an end-to-end pairing, being connected by attachment plaques. The X_1X_2X_3X_4X_5Y system of M. ferruginea arose by rearrangement between the homomorphic sex chromosome pair and an autosome. Multiple X Chromosomes and the sex chromosome pair do not differ from autosomes in a pattern of constitutive heterochromatin. Ultrastructural data on sex chromosome pairing in other spiders indicate that the homomorphic sex chromosome pair forms an integral part of the spider sex chromosome systems. It is suggested that this pair represents ancestral sex Chromosomes of spiders, which generated multiple X Chromosomes by non-disjunctions. Structural differentiation of newly formed X Chromosomes has been facilitated by heterochromatinization of sex chromosome bivalents observed in prophase I of spider females.
Isamu Hayata - One of the best experts on this subject based on the ideXlab platform.
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Characterization of ionizing radiation-induced ring Chromosomes by atomic force microscopy.
Analytical Biochemistry, 2004Co-Authors: Masahiro Murakami, Masako Minamihisamatsu, Reiko Kanda, Isamu HayataAbstract:We applied atomic force microscopy (AFM) to the structural analysis of radiation-induced ring Chromosomes. Constrictions observed on the metaphase ring chromosome were found to correspond to the centromere regions of the ring chromosome in comparison with the AFM image of the centromere of rod Chromosomes and with the fluorescence in situ hybridization (FISH) technique. Section analysis by AFM revealed that some ring-like chromosome fragments and ring-like chromatid fragments were thicker than standard Chromosomes or chromatids, suggesting that they were ring Chromosomes viewed edge on. Topographic analysis by AFM makes it possible to distinguish a ring viewed edge on that is difficult to recognize as a ring by light microscopy and to discriminate between a centric ring chromosome and an acentric ring chromosome using the same slides prepared for light microscopy.
Riccardo Crebelli - One of the best experts on this subject based on the ideXlab platform.
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Sex chromosome loss and non-disjunction in women: analysis of chromosomal segregation in binucleated lymphocytes.
Chromosoma, 1996Co-Authors: Andrea Zijno, Francesca Marcon, Paola Leopardi, Riccardo CrebelliAbstract:Chromosomal lagging and non-disjunction are the main mechanisms of chromosomal malsegregation at mitosis. To date, the relative importance of these two events in the genesis of spontaneous or induced aneuploidy has not been fully elucidated. A methodology based on in situ hybridization with centromeric probes in binucleated lymphocytes was previously developed to provide some insight into this matter. With this method, both chromosomal loss and non-disjunction can be simultaneously detected by following the distribution of specific Chromosomes in the nuclei and micronuclei of binucleated cells. In this study, this approach was used for studying the role of chromosomal loss and non-disjunction in the age-related malsegregation of sex Chromosomes in females. For this purpose, cultures of cytokinesis-blocked lymphocytes were established from 12 healthy women ranging in age from 25 to 56. The occurrence of malsegregation of X Chromosomes in vitro was estimated in binucleated cells that contained four signals, which orginates from the division of normal disomic cells. In this cell population, the frequencies of X chromosome loss and non-disjunction ranged from 0% to 1.69% (mean 0.75%), and from 0.20% to 1.33% (mean 0.57%), respectively. This indicates that both events contribute to malsegregation of X Chromosomes in vitro. Moreover, a small but not negligible fraction of binucleated cells with two or six copies of the X chromosome was noticed in all donors. These cells, which are thought to arise from parental monosomic and trisomic types, may indicate the malsegregation of X Chromosomes in vivo. The frequency of X chromosome aneuploidy both in vivo and in vitro significantly correlated with the age of donors. Analysis of chromosomal distribution in unbalanced cells demonstrated that both X homologues were frequently involved. The frequency of such multiple events (0.17%) was far greater than that expected by mere chance, indicating a tendency to multiple malsegregation events in the cell population investigated. Finally, parallel analysis of the segregation of chromosomex X and 1 in five of the donors confirmed the greater (about tenfold) susceptibility of X Chromosomes to malsegregate compared with autosomes.
