code: def remove_gaps(A, B):
      
      a_seq, b_seq = [], []
      for a, b in zip(list(A), list(B)):
          if a == '-' or a == '.' or b == '-' or b == '.':
              continue
          a_seq.append(a)
          b_seq.append(b)
      return ''.join(a_seq), ''.join(b_seq)
docs: skip column if either is a gap