The Linear Array mtDNA HVI/HVII Region-Specific Typing Kit (Roche Applied Science) is a sequence-specific oligonucleotide hybridization technique.²⁸ This technique is used as a screening assay and eliminates the need to perform more costly direct sequencing of all samples.

The linear array assay has sequence-specific oligonucleotide (SSO) probes immobilized on a membrane very similar in design to the AmpliType PM + DQA1 Typing Kit.²⁹ Biotinylated PCR (Polymerase Chain Reaction) products hybridize to the SSO probes with the exact sequence complement.  Common polymorphic sites are interrogated.²⁸ All biotinylated PCR products hybridized to the SSO probes are detected with streptavidine-horseradish peroxidase conjugate. A chromogenic substrate produces a blue precipitate on the membrane. It is this pattern of "thin blue lines" that detects sequence variants to the rCRS. All samples not excluded with this typing kit can be analyzed with direct sequencing methods to evaluate the full hypervariable regions, using the original amplicons. Data is reviewed to obtain additional sequence information to confirm the original match or determine it to be a non-match.

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