1/21/2024 0 Comments Hybrid crossover brake repairBreak points on chromosomes can be localized by Giemsa banding or with the help of special FISH techniques ( Sumner, 1990 Holmquist, 1992 Folle and Obe, 1995, 1996 Bickmore and Craig, 1997 Folle et al., 1997 Martinez-López et al., 1998 Johannes et al., 1999). Studies on radiation-induced CA in G 0/G 1 cells using the FISH methodology revealed that chromosomal rearrangements may be complex, involving three or more breaks in two or more chromosomes ( Brown and Kovacs, 1993 Lucas and Sachs, 1993 Savage and Simpson, 1994a, b Simpson and Savage, 1994, 1995a, b Griffin et al., 1995, 1996 Tucker et al., 1995 Savage, 1996, 1997 Savage and Tucker, 1996 Edwards and Savage, 1999 Johannes et al., 1999 Simpson et al., 1999). Other CA types, such as reciprocal translocations and inversions, are normally not recognizable with Giemsa staining but can be visualized by fluorescence in situ hybridisation (FISH) ( Lucas et al., 1989, 1992, 1997 Gray et al., 1994 Natarajan et al., 1994, 1996a, b Gebhart et al., 1996 Boei et al., 1998 Chudoba et al., 1999 Johannes et al., 1999 Knehr et al., 1999 Wojcik et al., 1999). Staining of chromosomes with Giemsa allows the analysis of different types of CA, such as polycentric chromosomes, ring chromosomes, chromatid interchanges and fragments. Fusion of mitotic cells with interphase cells induces premature chromosome condensation (PCC) in the latter which permits the analysis of chromosomes at stages in which they are normally not visible ( Rao et al., 1982 Cornforth, 1998). In general, CA are analysed in mitosis at a metaphase-like stage that is induced by colchicine ( Levan, 1938). The first class comprises aberrations within a single chromosome, such as terminal and interstitial deletions and inversions the second class comprises rearrangements between two or more chromosomes, such as translocations and dicentrics. CA can be classified as intra- and inter-chromosomal aberrations. Sometimes, alterations in the normal chromosome structure, so-called chromosomal aberrations (CA), are observed. In meiosis, only one S phase takes place in the pre-meiotic cell cycle, followed by two meiotic divisions that separate the homologues and the sister chromatids, respectively. After extensive research it became clear that, with few exceptions, G 0/G 1 chromosomes contain one DNA molecule which is replicated in the S phase of the mitotic cell cycle to yield two sister chromatids, each of which consists of one single DNA molecule (the uninemic structure of chromosomes). In most cells chromosomes are visible only during the process of cell division ( Cremer et al., 1996 Savage, 1996 Bickmore and Craig, 1997 Kreth et al., 1998 Wolffe, 1998). Chromosomes consist mainly of DNA, histones and non-histone proteins and are organized during interphase in domains.
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