Exact probability of fixed patterns occurring in a random sequence

We derive a procedure to obtain the exact probability that a specific pattern of letters occurs in a longer random sequence of letters. The procedure is generalized to find the exact probability of a fixed (specific) single pattern, and a union or intersection of multiple fixed (specific) patterns within a random sequence perfectly for any distributions of a cell in the random sequence, and can handle patterns with uncertain letters (including missing, blank, unclear, ambiguous, transposition, etc.). The procedure also finds the probability that a pattern that is randomly picked will appear in a separate longer random sequence of letters. These methods are of particular applicability in genetic sequence analysis, diagnostics, anthropology, clinical medicine, data mining, computational molecular biology, and pattern analysis and recognition.