(a) Explain the role of guide trees in progressive multiple sequence alignment algorithms.
What do the leaf and internal nodes of a guide tree represent?
(b) Determine the sum-of-pairs scores for the following multiple sequence alignment of DNA sequences, using the scoring matrix in which a match gets a value of +4, a mismatch gets a value of -1, a (base,-) pair gets a value of -2, and a (-,-) pair gets a value of 0.
GT - A
C - - A