Final answer:
Southern blotting is a molecular biology technique (Option B) used to detect specific DNA sequences by separating DNA fragments on a gel, transferring them to a nylon membrane, and then probing with a complementary DNA probe.
Step-by-step explanation:
The correct answer for the question "Which best describes Southern blotting" is: Southern blotting is used to detect the presence and quantity of various DNA strands in a sample. In the Southern blot technique, DNA fragments within a sample are first separated by agarose gel electrophoresis based on their size and charge, then transferred to a thin, positively charged membrane made of nitrocellulose or nylon through capillary action. Once transferred, the DNA fragments on the membrane are probed with a specific single-stranded DNA probe labeled with a radioactive or fluorescent marker. This process allows for the detection of specific DNA sequences within the DNA sample. The other options provided are incorrect as (A) describes the polymerase chain reaction (PCR), which is used for amplifying DNA sequences, (C) refers to the Sanger sequencing method that uses dideoxynucleotides to terminate the DNA chain, and (D) describes the gel electrophoresis step, which is part of Southern blotting but not the complete process itself.