▁high - sc oring ▁words . ▁ ▁The ▁B LA ST ▁program ▁sc ans ▁the ▁database ▁sequences ▁for ▁the ▁remaining ▁high - sc oring ▁word , ▁such ▁as ▁P EG , ▁of ▁each ▁position . ▁If ▁an ▁exact ▁match ▁is ▁found , ▁this ▁match ▁is ▁used ▁to ▁seed ▁a ▁possible ▁un - g apped ▁alignment ▁between ▁the ▁query ▁and ▁database ▁sequences . ▁ ▁Ext end ▁the ▁exact ▁matches ▁to ▁high - sc oring ▁segment ▁pair ▁( H SP ). ▁ ▁The ▁original ▁version ▁of ▁B LA ST ▁st ret ches ▁a ▁longer ▁alignment ▁between ▁the ▁query ▁and ▁the ▁database ▁sequence ▁in ▁the ▁left ▁and ▁right ▁directions , ▁from ▁the ▁position ▁where ▁the ▁exact ▁match ▁occurred . ▁The ▁extension ▁does ▁not ▁stop ▁until ▁the ▁accum ulated ▁total ▁score ▁of ▁the ▁H SP ▁begins ▁to ▁decrease . ▁A ▁simplified ▁example ▁is ▁presented ▁in ▁figure ▁ 2 . ▁▁ ▁To ▁save ▁more ▁time , ▁a ▁newer ▁version ▁of ▁B LA ST , ▁called ▁B LA ST 2 ▁or ▁g apped ▁B LA ST , ▁has ▁been ▁developed . ▁B LA ST 2 ▁adopt s ▁a ▁lower ▁neighborhood ▁word ▁score ▁threshold ▁to ▁maintain ▁the ▁same ▁level ▁of ▁sens itivity ▁for ▁detect ing ▁sequence ▁similarity . ▁Therefore , ▁the ▁possible ▁matching ▁words ▁list ▁in ▁step ▁ 3 ▁becomes ▁longer . ▁Next , ▁the ▁exact ▁matched ▁regions , ▁within ▁distance ▁A ▁from ▁each ▁other ▁on ▁the ▁same ▁diagonal ▁in ▁figure ▁ 3 , ▁will ▁be ▁joined ▁as ▁a ▁longer ▁new ▁region . ▁Finally , ▁the ▁new ▁regions ▁are ▁then