Chromosome banding techniques

During mitosis, aU the DNA is highly condensed to allow separation of the sister chromatids. This is the only time in the ceE cycle when the chromosome structure is visible. Chromosome abnormalities may be assessed on mitotic chromosomes by karyotype analysis (metaphase chromosomes) and by banding techniques (prophase or prometaphase), which identify aneu-ploidy, translocations, deletions, inversions, and duplications. 

Other modifications that may be introduced here relate to preparation of chromosomes for banding. Procedures for specific banding techniques should be consulted. 

Kuoerova, M. Polivkova, Z. (1976) Banding technique used for the detection of chromosomal aberrations induced by radiation and alkylating agents TEPA and epichlorohydrin. Mutat. Res., 34, 279-290... 

At the cytological level, the power and resolution of a variety of chromosome staining and banding techniques has been increased by ihcir application to prophase chromosomes and the genetic map now locates over one thousand bands. At the nuclcosomal level, the association of DNA with histone proteins is reasonably well understood. However, knowledge of the higher order structure and the nature of the association between DNA and the acidic structural scaffold, or core proteins, of the chromosome, remains unresolved. 

Menasce LP, White GR, Harrison CJ, Boyle JM. Localization of the estrogen receptor locus (ESR) to chromosome 6q25.1 by FISH and a simple post-FISH banding technique. Genomics 1993 17(l) 263-265. 

Another use of polyfene chromosomes is microdissection of DNA for cloning (Fig. 26-14). A piece of DNA confaining 100-400 kb can be cut out of any desired spof, cleaved with restriction enzymes, and cloned. 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. The technique has been extended to human and other mammalian chromosomes. ... 

The degree of resolution of the banding techniques depends on the degree of elongation of heterochromatic regions. Thus, for all of the banding procedures described below, chromosomes should be prepared according to Protocol 1.2, with the omission of colchicine treatment. 

Funaki K., Matsui S., and Sasaki M. 1975. Location of nucleolar organizers in animal and plant chromosomes by means of an improved N-banding technique. Chromosoma 49 357-370. 

Note Air-dried slides can be stained with a variety of dyes, processed for chromosome banding, or used for in situ hybridization. For a detailed account of these techniques, see PimpineUi et al. (this volume). 

Garson, J A, van den Berghe, J. A., and Kemshead, J. T. (1987) Novel nonisotopic m situ hybridization technique detects small (1 kb) unique sequences in routinely G-banded human chromosomes, fine mapping of N-MYC and b-NGF genes. Nucleic Acids Res 15,4761-4770... 

There has been much discussion about the potential utility of flow cytometry of chromosomes for clinical diagnosis. As regards its sensitivity, this technique appears to stand somewhere between the technique of flow analysis of whole cells for DNA content and that of microscope analysis of banded chromosomes. It may be a useful intellectual exercise for readers to ask themselves which technique or techniques would be most appropriate for detecting the following types of chromosome abnormalities (1) tetraploidy, where the normal chromosome content of cells is exactly doubled because of failure of cytokinesis after mitosis (2) an inversion in an arm of one particular chromosome and (3) trisomy (the existence of cells with three instead of two) of one of the small chromosomes. In addition to these limitations, the use of flow cytometry to look for abnormal chromosomes has been confounded by the fact that several human chromosomes are highly polymorphic, and flow karyotypes, therefore, vary considerably among normal individuals. 

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