Getting DNA out of blood
Red blood cells do not have any DNA, as they lose their nuclei (the compartment in a cell that contains the DNA) as they mature. So the DNA in your blood is in your white blood cells. To get at it, scientists first spin a small sample of your blood at high speed, to separate the cells from the blood fluid. Next, they release the DNA from the cells using a detergent and a special enzyme. Finally, they add alcohol, which makes your DNA appear as sticky blob in the mixture.