Overview of DNA library preparation for deep sequencing. The purified genomic DNA is processed and modified as described in the basic protocols. The adapter-modified DNA fragments (library) are then enriched through PCR. Note the relative positions and characteristics (Inset) of the InPE1.0, InPE2.0 and the Index primers used during PCR. For multiplexed paired-end PCR, the same InPE1.0 and InPE2.0 primers are used, however, up to 12 different Index primers can be added to the enrichment reactions individually. Sequencing is performed in one direction through sequencing by synthesis, and then in the alternate direction as described in the background information. The complementary sequences are shaded darker.