= Solution
The number specifies the sequence-identity threshold used when clustering related sequences before deriving a <BLOSUM> <substitution matrix>. At 62%, sufficiently similar sequences are grouped and their within-cluster comparisons are excluded. Lowering the threshold merges more sequences, emphasizing comparisons across greater divergence.
Consequently \b[BLOSUM80 is suited to closer relatives, BLOSUM45 to more divergent sequences, and <BLOSUM62> is intermediate]. The numbers do not specify a required identity of the query and target, nor a number of evolutionary time steps.<Amino acid substitution matrices from protein blocks by Steven Henikoff and Jorja G. Henikoff>[pp. 10916–10917, clustering levels and performance across divergence]{ref}
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