The Needleman-Wunsch method for aligning DNA sequences assigns 1 point whenever a mis-

match occurs, and 3 points whenever a gap (insertion or deletion) appears in a sequence. Assume that under certain conditions, the number of mismatches has mean 5 and standard deviation 2, and the number of gaps has mean 2 and standard deviation 1.

a. Find the mean of the Needleman-Wunsch score.

b. Assume the number of gaps is independent of the number of mismatches. Find the variance of the Needleman-Wunsch score.

Answer :

Step 1 of 3 :

Given,

We have a method called Needleman - Wunsch method for aligning DNA sequences .

Which assigns 1 point whenever a mismatch occurs, and 3 points whenever a gap appears in a sequence.

We have to assume that the certain conditions, the number of mismatches has mean 5 and standard deviation 2. ( = 5 and = 5 )

The number of gaps has mean 2 and standard deviation 1.( = 2 and = 1 )

Let S denotes the Needleman-Wunsch score, then S = X + 3Y