Scientist adding ice-cold water to a blood sample prior to DNA preparation, Great Ormond Street Hospital, May 2000. Red blood cells do not contain DNA as they lose their nucleii (the compartment in a cell that contains the DNA) as they mature. Blood DNA is contained in the white blood cells. To extract it, a small sample of blood is spun at high speed to separate the cells from the blood fluid. Next, the DNA is released from the cells using a detergent and a special enzyme. Finally, alcohol is added, which makes the DNA appear as a sticky blob in the mixture.
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