5 ml of blood is removed from the patient.   If a fetus is being karyotyped amniotic fluid is removed from the amniotic sac which surrounds the fetus during development. This is done with the aid of a large syringe and ultrasound picturing. There are cells which have come off the fetus in this fluid. The white blood cells are removed from the blood or the living cells are removed from the amniotic fluid. These cells are then cultured in a medium in which they undergo mitosis. Mitosis is stopped at metaphase using chemicals. The cells are then placed onto a slide and spread out. They are viewed under a microscope which is specially adapted with a camera to take a picture of the chromosomes from one of the cells. Once the picture is taken and enlarged the chromosomes are cut out and arranged in pairs according to size and location of the centromere.

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