1. A method of sequencing comprising: sequencing a plurality of genomic fragments, wherein the genomic fragments are obtained from a plurality of different sources, and wherein: i. each of said genomic fragments comprises an oligonucleotide tag that comprises a unique nucleotide sequence that indicates from which source a genomic fragment is derived; and, separate from said unique nucleotide sequence, a binding site for a sequencing primer; ii. said sequencing of the plurality of genomic fragments is done using said sequencing primer; and iii. said genomic fragments correspond to one or more selected portions of a genome that have been isolated from a pooled genomic sample by specific hybridization; to obtain, for each of the sequenced fragments, the unique nucleotide sequence of an oligonucleotide tag and the nucleotide sequence of at least a portion of a genomic fragment.