Schematic of one form of targeted NGS. The process starts by randomly cutting genomic DNA (or cDNA) into short fragments (a few hundred base pairs in length); oligonucleotide linkers are added to the fragments to generate a library in vitro; libraries are hybridized to oligonucleotides specific to the targeted genetic region; DNA fragments not interacting with the target are washed away; libraries are introduced into a microscope slide with flow channels containing complementary oligonucleotides on the surfaces of the channel to ones on the libraries, thus allowing hybridization to attach millions of individual molecules to discrete locations on the slide; in situ polymerase chain reaction is performed to copy the individual fragments of the library to enhance sequencing detection; single base extension by a DNA polymerase with all four dye terminators extends the sequence one base, the image of the base extension is captured, and this cycle is repeated 100 times from one end of the molecule and 100 times from the other; DNA sequences are assembled and variants different from the reference(s) identified; and blood group gene variants are annotated using phenotype-genotype databases, population frequencies, and computational tools. Adapted with permission from Johnsen et al.³⁹