Dideoxy DNA sequencing or Sanger sequencing is used to determine the nucleotide sequence of a DNA fragment, where the elongation or polymerization process is halted by the introduction of ddNTPs. Therefore, by using four different types of ddNTPs, such as ddATP, ddCTP, ddGTP, and ddTTP, one can halt polymerization at known sites for each nucleotide type. The final result is a mix of DNA fragments with different lengths, which can be separated on the basis of molecular weight. Thus, by combining the data from all four categories, it is possible to determine the sequence of the DNA fragment.
Southern blotting is also used to study DNA but for different purposes. The experiment involves the use of endonucleases in order to create oligonucleotides, which are cut at specific sequence regions in order to be able to create short fragments of DNA. Such a process allows for the creation of a DNA library or for observing the number of genes present in the DNA.