Mammalian chromosome

At metaphase, mammalian chromosomes possess a twofold symmetry, with the identical duplicated sister chromatids connected at a centromere, the relative po-... 

Stratmann R, Lehner CF 1996 Separation of sister chromatids in mitosis requires the Drosophila pimples product, a protein degraded after the metaphase/anaphase transition. Cell 84 25-35 Sumner AT 1991 Scanning electron microscopy of mammalian chromosomes from prophase to telophase. Chromosoma 100 410-418... 

In vitro mammalian chromosome aberration test OECD,US... 

Van Hooser A, Goodrich DW, Allis CD, Brinkley BR, Mancini MA (1998) Histone H3 phosphorylation is required for the initiation, but not maintenance, of mammalian chromosome condensation. J Cell Sci lll(Pt 23) 3497-3506... 

Y. B. Yurov, and N. A. Liapunova, The units of DNA replication in the mammalian chromosomes evidence fora large size of replication units. Chromosoma 60, 253-267 (1977). 

In Vitro Mammalian Chromosomal Aberration Test (Updated Guideline, adopted 21 July 1997)... 

B.IO Mutagenicity - In Vitro Mammalian Chromosome Aberration Test (20(X))... 

Another use of polytene chromosomes is microdissection of DNA for cloning (Fig. 26-14). A piece of DNA containing 100-400 kb can be cut out of any desired spot, cleaved with restriction enzymes, and cloned.282 Since it has been estimated that Drosophila may contain only -9000-17,000 genes there may be 2-3 genes per band in these chromosomes.283 The technique has been extended to human and other mammalian chromosomes.284... 

Developmental rats, rabbits Prenatal and postnatal development none Genetic toxicology Ames test, in vitro mammalian chromosome aberration test in V79 Chinese hamster cells, and in vivo mammalian erythrocyte micronucleus test in rats... 

Mammalian chromosome aberration test in vitro CA in vitro Chromosome aberrations Mainly structural alterations (chromosome or chromatid)... 

Mitelman F (ed) (1995) An International System for Human Cytogenetic Nomenclature Recommendations of the International Standing Committee on Human Cytogenetic Nomenclature. S. Karger, Basel EEC Directive 2000/32/EC, L 136, B.10., Mutagenicity-/n Vitro Mammalian Chromosome Aberration Test. Adopted 19-May-2000... 

OECD (1997) Guideline For Testing Of Chemicals, 473 Genetic Toxicology In Vitro Mammalian Chromosome Aberration Test . Adopted 21-Jul-1997 U.S. EPA (1998) OPPTS 870.5375 Health Effects Test Guidelines In Vitro Mammalian Chromosome Aberration Test, August 1998... 

Parelho V, et al. Cohesins Functionally associate with CTCF on mammalian chromosome arms. Cell 2008 132 422-433. 

Nil. Neel, J. V., The hemoglobin genes a remarkable example of the clustering of related genetic functions on a single mammalian chromosome. Blood 18, 769-777 (1961). 

Cell tines offer several advantages over primary cell cultures, such as an unlimited life-span and the lack of time-consuming isolation procedures. Additionally once established, they are often more stable than primary cells which are usually in a continuous state of de-differentiation. Thus, the majority of in vitro nephrotoxicity studies have been performed on renal epithelial cell tines. In normal somatic cells, telomeres, the tandemly repeated hexamers at the end of mammalian chromosomes, act as the cellular replicative clock [43] and shorten at each cell division. Once telomeres have exceeded a certain critical length, the so called "Hayflick limit" [44], the cell enters replicative senescence and no longer proliferates. Until recently the most widely used renal cell tines were those which arose from spontaneously acquired immortalization in culture. These cell tines include LLC-PK (Hampshire pig) [45,46], JTC-12 (cynomolgus monkey) [47] and OK (American opossum) [48] cells, which exhibit biochemical and antigenic characteristics suggestive of proximal... 

Clare G (2012) The in vitro mammalian chromosome aberration test. Methods Mol Biol 817 69-91... 

OECD (1997) Test No. 473 In Vitro Mammalian Chromosome Aberration Test OECD Publishing... 

Given that the chromosomes ol mammalian cells may be 20 times as large as those of Escherichia coli, how can replication of mammalian chromosomes be carried out in just a few minutes ... 

Mammalian chromosomes have specialized structures with highly repetitive DNA at their ends (telomeres). Which aspect of telomeric DNA replication is different from that of other chromosomal regions ... 

The answer is c. (Murray, pp 412-434. Scriver, pp 3-45. Sack, pp 3—29. Wilson, pp 99-121.) Despite the great length of the chromosomes of eukaryotic DNA, the actual replication time is only minutes. This is because eukaryotic DNA is replicated bidirectionally from many points of origin. The hundreds of initiation sites for DNA replication on chromosomes share a consensus sequence called an autonomous replication sequence (ARS). Thus, while the process of DNA replication in mammals is similar to that in bacteria, with DNA polymerases of similar optimal temperatures and speed, the many replication forks allow for a rapid synthesis of chromosomal DNA. Proteins such as histones, which are bound to mammalian chromosomes, inhibit DNA replication or transcription. Dissociation of the protein-DNA complex (chromatin) and unwinding of DNA supercoils (followed by chromatin reassembly) is part of the replication process. 

The answer is a. (Murray, pp 435-451. Scriver, pp 3-45. Sack, pp 1-40. Wilson, pp 101-120.) In mammals, RNA polymerase binds to promoter sites upstream from the start site. These include the TATA box (TATAAT), the CAAT box, and the GC box. DNA primase and helicase are involved in DNA replication and do not bind specifically to sequences upstream of genes. Restriction endonucleases recognize specific sequences in double-helical DNA and cleave both strands. Histones nonspecifically bind to chromosomal DNA and constitute about half the mass of mammalian chromosomes. 

The amount of DNA required per dot depends on the number of target sequences present. For single-copy genes in mammalian chromosomes, detection is achieved with 1-10 pg of total target nucleic acid. Proportionately less can be used when multiple copies are... 

Gene mutations are a necessary, if not sufficient, inducer of the tumorigenic process. The test is mechanistically simple and the easiest to perform, and it has been validated more extensively than the other tests. It is also less susceptible than the in vitro mammalian cell tests to artifactual positive results. Despite the fact that the bacterial chromosome is structurally and functionally different from the mammalian chromosome, substances that directly damage or adduct nucleotides in the DNA helix would be expected to act similarly in both chromosome types. E. coli mutation tests are performed in addition to Salmonella for some regulatory needs (Gatehouse et al. 1994). 

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