tokens: Genomic DNA was extracted using lysis buffer containing 20 mM Tris - HCl , pH 7 . 5 ; 0 . 4 M NaCl ; 0 . 5 % SDS ; 10 mM EDTA , treated with proteinase K ( 200 mu g / mu l ) , purified with phenol / chloroform , precipitated with ethanol and dissolved in DNase free water .