What is a chromosome analysis?
Chromosomal analysis is a cytogenetic method used to detect numerical or structural chromosomal aberrations. Such an analysis would be used, for example, in cases of immediate suspicion of a chromosomal syndrome, i.e. malformations (dysmorphies) or mental retardation (retardation), but also in infertility, regular miscarriages (abortions) and also certain types of cancer (e.g. lymphomas or leukaemias).
This usually requires lymphocytes, a special type of immune cells that are obtained from the patient’s blood. Since only a comparatively small amount can be obtained in this way, the cells are stimulated to divide with phytohaemagglutinin and can be used to grow lymphocytes in the laboratory. In some cases, samples (biopsies) of skin or spinal cord are taken instead, which are treated in a very similar way.
The aim is to obtain as much DNA material as possible, which is currently in the middle of cell division. In the metaphase, all chromosomes arrange themselves in one plane approximately in the middle of the cell, in order to be drawn to the opposite sides (poles) of the cell in the next step, the anaphase. At this point, the chromosomes are particularly densely packed (highly condensed).
The spindle poison colchicine is added to this, which acts precisely in this phase of the cell cycle so that the metaphase chromosomes accumulate. They are then isolated and stained using special staining methods. The most common is GTG banding, in which the chromosomes are treated with trypsin, a digestive enzyme, and the dye Giemsa.
In this process, the particularly densely packed and the regions rich in adenine and thymine are darkened. The resulting G-bands are characteristic for each chromosome and, in simple terms, are considered to be the more gene-poor regions. An image of the stained chromosomes is taken at a thousand-fold magnification and a karyogram is generated with the aid of a computer program.
In addition to the band pattern, the size of the chromosome and the position of the centromere are used to arrange the chromosomes accordingly. There are also other banding methods which can have very different advantages.
