Differential Extraction • The sperm are subsequently lysed by treatment with a SDS/proteinase K/ dithiothreitol (DTT) mixture. The DTT is required to breakdown (reduce) the protein disulfide bridges that make up the sperm head. The sperm are impervious to lysis without the addition of the DTT. • Both the male fraction and the female fraction are then extracted with phenol-chloroform, and the DNA precipitated with ethanol.