Editing Comparative genomic hybridization (section)

===Metaphase slide preparation===
The DNA on the slide is a reference sample, and is thus obtained from a karyotypically normal man or woman, though it is preferential to use female DNA as they possess two X chromosomes which contain far more genetic information than the male Y chromosome. Phytohaemagglutinin stimulated peripheral blood lymphocytes are used. 1mL of heparinised blood is added to 10ml of culture medium and incubated for 72 hours at 37&nbsp;°C in an atmosphere of 5% CO<sub>2</sub>. Colchicine is added to arrest the cells in mitosis, the cells are then harvested and treated with hypotonic [[potassium chloride]] and fixed in 3:1 [[methanol]]/[[acetic acid]].<ref name="Weiss,Hermsen,Meijer,VanGrieken,Baak,Kuipers,VanDiest" />

One drop of the cell suspension should then be dropped onto an ethanol cleaned slide from a distance of about 30&nbsp;cm, optimally this should be carried out at room temperature at humidity levels of 60–70%. Slides should be evaluated by visualisation using a phase contrast microscope, minimal cytoplasm should be observed and chromosomes should not be overlapping and be 400–550 bands long with no separated [[chromatids]] and finally should appear dark rather than shiny. Slides then need to be air dried overnight at room temperature, and any further storage should be in groups of four at −20&nbsp;°C with either [[Silicon dioxide|silica]] beads or [[nitrogen]] present to maintain dryness. Different donors should be tested as hybridization may be variable. Commercially available slides may be used, but should always be tested first.<ref name="Weiss,Hermsen,Meijer,VanGrieken,Baak,Kuipers,VanDiest" />