To solve this problem, we need to identify which technique is not used in the Southern hybridization process. Let's analyze each option:$\newline \bullet$Option 1: Electrophoresis$\newline$ - Electrophoresis is used to separate DNA fragments based on size.$\newline$ - It is an essential step in Southern hybridization to resolve DNA fragments before transferring them to a membrane.$\newline$ - Therefore, electrophoresis is used in Southern hybridization.$\newline \bullet$Option 2: Blotting$\newline$ - Blotting refers to the transfer of DNA fragments from a gel to a membrane.$\newline$ - This step is crucial in Southern hybridization to immobilize DNA for hybridization with a probe.$\newline$ - Therefore, blotting is used in Southern hybridization.$\newline \bullet$Option 3: Autoradiography$\newline$ - Autoradiography is used to detect labeled DNA fragments on a membrane.$\newline$ - It involves exposing the membrane to an X-ray film to visualize hybridized DNA.$\newline$ - Therefore, autoradiography is used in Southern hybridization.$\newline \bullet$Option 4: PCR$\newline$ - PCR (Polymerase Chain Reaction) is a technique used to amplify DNA sequences.$\newline$ - It is not a part of the Southern hybridization process, which involves the detection of specific DNA sequences rather than amplification.$\newline$ - Therefore, PCR is not used in Southern hybridization.$\newline$Based on the analysis, the correct option is Option 4: PCR, as it is not used in the Southern hybridization technique.