code: def append_flanking_markers(qtls_mk_file, flanking_markers):
      
      matrix = read_input_file(qtls_mk_file, sep=',')
      output = []
      cnt = 0
      for row in matrix:
          if cnt == 0:
              markers = ['LOD2 interval start', 'LOD2 interval end']
          elif row[3] in flanking_markers:
              markers = flanking_markers[row[3]]
          else:
              markers = ['NA', 'NA']
          cnt += 1
          row.extend(markers)
          output.append(row)
      write_matrix(qtls_mk_file, output)
docs: Append the flanking markers extracted in the process of
      generating the MapChart to the QTL list file.