Nucleic acid sequencing

A method for determining a plurality of target nucleic acid sequences, which method comprises the steps of:

• (a) contacting a preparation wherein the plurality of target nucleic acid sequences is comprised in the preparation and further comprising a plurality of corresponding non-target nucleic acid sequences, each target nucleic acid sequence in the preparation corresponds to one or more corresponding non-target nucleic acid sequences in the preparation, each target nucleic acid sequence and each corresponding non-target nucleic acid sequence has a first region of common sequence upstream of a first region of dissimilar sequence upstream of a second region of dissimilar sequence, the first region of common sequence of each target nucleic acid sequence is the same as the first region of common sequence of its corresponding non-target nucleic acid sequences, the first region of dissimilar sequence of each target nucleic acid sequence is different to the first region of dissimilar sequence of its corresponding non-target nucleic acid sequences, the second region of dissimilar sequence of each target nucleic acid sequence is different to the second region of dissimilar sequence of its corresponding non-target nucleic acid sequences,—with a plurality of blocking oligonucleotides wherein each blocking oligonucleotide is complementary to at least a portion of the first region of dissimilar sequence of a non-target nucleic acid sequence, under conditions to hybridise the blocking oligonucleotide thereto;
• (b) contacting the resultant preparation with a plurality of sequencing primers, wherein each primer is complementary to at least a portion of the first region of common sequence of a target nucleic acid sequence and its corresponding non-target nucleic acid sequence, under conditions to hybridise the primer thereto;
• and
• (c) subjecting the so treated preparation to a sequencing reaction, such that the sequencing reaction proceeds into the second region of dissimilar sequence of the target nucleic acid sequences, thereby determining at least the second region of dissimilar sequence of each target nucleic acid sequence;
• and wherein the blocking oligonucleotides block the sequencing reaction at least from proceeding into the second region of dissimilar sequence of each corresponding non-target nucleic acid sequence.