Chromosomes are studied in peripheral blood lymphocytes, but almost any tissue can act as a sample.
T-lymphocytes are firstly stimulated to transform and divide with phytohaemagglutinin. Division is is arrested after 48-72 hours. After air-drying on a microscope slide, staining is carried out. Routinely, Giemsa stain is used so as to produce a series of light and dark bands specific for individual chromosomes.
Recently, the technique of flow cytometry has been applied to kayotyping. A suspension of chromosomes is stained with a fluorescent dye and then passed through laser light. A photomultiplier on the other side detects transmitted light. Cumulative histograms of transmittance are established after many chromosomes have passed through. The position and height of each peak is characteristic of a certain chromosome. In this way, flow karyotyping can detect chromosomal aberrations.
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