Sequencing from PCR - Biology

All sequencing methods, be it classical Sanger sequencing or next-generation sequencing (or even third generation) need a certain amount of DNA to work with.

You either need to extract DNA from a large-ish tissue sample or you need to amplify DNA content from a smaller sample. The first approach is often impractical, or downright impossible (when you want to work with single cells or very small organisms).

So PCR is used routinely to amplify DNA before sequencing. The sequencing itself isn’t influenced by this – you use whatever technique is appropriate. However, the PCR may introduce biases into the data because not all DNA fragments amplify equally efficiently. This needs to be taken care of in the downstream analysis of the sequence data if quantitative information is required (as in RNA-seq or ChIP-seq).

Coming back to your question, PCR isn’t a sequencing method in itself. It just helps getting the necessary amount of raw material in order for sequencing to work. Furthermore, most sequencing methods actually include PCR steps as well, since they rely on the generation of of overlapping DNA fragments to be stitched together.