Point accepted mutation

Point Accepted Mutation (PAM) is the point mutation per 100 amino acids. PAM1 means a 1 point mutation/100 amino acids. A PAM matrix is usually a 20 by 20 matrix which gives the different rates of mutations between pairs of amino acids. This PAM matrix is a type of substitution matrix that is used in sequence alignment and multiple sequence alignment. Different PAM matrices are derived from the multiplication of the PAM1 matrix. A PAM250 is equivalent to 1 unchanged amino acid out of 5.

The concept of PAM and PAM matrices was first developed by Margaret Dayhoff.


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