BLOSUM62 is a BLOSUM amino-acid substitution matrix constructed using a 62-percent sequence-identity clustering threshold for the contributing blocks. It is widely used in protein sequence alignment. Its substitution scores form only one part of a complete alignment scheme: gap costs and local versus global objectives also affect the result. The number 62 describes construction of the matrix rather than a required identity of the query and target. [ref]
Amino acid substitution matrices from protein blocks by Steven Henikoff and Jorja G. Henikoff. 1992, BLOSUM family and clustering thresholds
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