be two random sequences so that every random variable takes values in a finite set A. We consider a global similarity score Ln := L(X 1 , . . . , Xn; Y 1 , . . . , Yn) that measures the homology (relatedness) of words (X 1 , . . . , Xn) and (Y 1 , . . . , Yn). A typical example of such score is the length of the longest common subsequence. We study the order of central absolute moment E|Ln − ELn| r in the case where the two-dimensional process (X 1 , Y 1 ), (X 2 , Y 2 ), . . . is a Markov chain on A × A. This is a very general model involving independent Markov chains, hidden Markov models, Markov switching models and many more. Our main result establishes a general condition that guarantees that E|Ln − ELn| r n r 2 . We also perform simulations indicating the validity of the condition.