docs: def ambiguate(sequence1, sequence2, delete_ambiguous=False):
      """ delete_ambiguous: Marks sequences for deletion by replacing all
      chars with 'X'. These seqs are deleted later with remove_empty """
      delete = False
      combination = list()
      z = list(zip(sequence1, sequence2))
      for (a, b) in z:
          if a == b:
              combination.append(a)
          else:
              if a == '-' or b == '-':
                  combination.append('-')
              else:
                  if delete_ambiguous:
                      delete = True
                  ambig = get_ambiguity(a, b)
                  combination.append(ambig)
      if delete:
          return 'X' * len(combination)
      return ''.join(combination)