▁ac ids , ▁these ▁extrem es ▁suggest ▁that ▁am ino ▁ac ids ▁are ▁more ▁likely ▁to ▁accept ably ▁mut ate ▁if ▁their ▁physical ▁and ▁chemical ▁properties ▁are ▁more ▁common ▁among ▁alternative ▁am ino ▁ac ids . ▁ ▁Const ruction ▁of ▁the ▁mut ation ▁matrix ▁ ▁For ▁the ▁th ▁am ino ▁acid , ▁the ▁values ▁ ▁and ▁ ▁are ▁its ▁mut ability ▁and ▁frequency . ▁The ▁frequencies ▁of ▁the ▁am ino ▁ac ids ▁are ▁normal ised ▁so ▁that ▁they ▁sum ▁to ▁ 1 . ▁If ▁total ▁number ▁of ▁occurr ences ▁of ▁the ▁th ▁am ino ▁acid ▁is ▁, ▁and ▁ ▁is ▁the ▁total ▁number ▁of ▁all ▁am ino ▁ac ids , ▁then ▁ ▁Based ▁on ▁the ▁definition ▁of ▁mut ability ▁as ▁the ▁ratio ▁of ▁mut ations ▁to ▁occurr ences ▁of ▁an ▁am ino ▁acid ▁ ▁or ▁▁ ▁The ▁mut ation ▁matrix ▁ ▁is ▁constructed ▁so ▁that ▁the ▁entry ▁ ▁represents ▁the ▁probability ▁of ▁the ▁th ▁am ino ▁acid ▁mut ating ▁into ▁the ▁th ▁am ino ▁acid . ▁The ▁non - di ag onal ▁entries ▁are ▁computed ▁by ▁the ▁equation ▁ ▁where ▁ ▁is ▁a ▁constant ▁of ▁proportional ity . ▁However , ▁this ▁equation ▁does ▁not ▁compute ▁the ▁diagonal ▁entries . ▁Each ▁column ▁in ▁the ▁matrix ▁ ▁lists ▁each ▁of ▁the ▁twenty ▁possible ▁out comes ▁for ▁an ▁am ino ▁acid ▁— ▁it ▁can ▁mut ate ▁into ▁one ▁of ▁the ▁ 1 9 ▁other ▁am ino ▁ac ids , ▁or ▁remain ▁un changed . ▁Since ▁the ▁non - di ag onal ▁entries ▁listing ▁the ▁prob abilities