tokens: One microliter of 20 % SDS was added to achieve mitochondrial lysis and the DNA was extracted with phenol / chloroform , precipitated with 0 . 1 vol of 3 M Sodium Acetate ( pH 5 . 2 ) , 3 vol of 100 % ethanol and 100 ng of carrier yeast tRNA and left overnight at - 20 degrees C .