def make_sequences(pdb_dict):
    """Creates a mapping of chain IDs to sequences, by parsing SEQRES records.

    :param dict pdb_dict: the .pdb dictionary to read.
    :rtype: ``dict``"""

    seq = {}
    if pdb_dict.get("SEQRES"):
        for line in pdb_dict["SEQRES"]:
            chain, residues = line[11], line[19:].strip().split()
            if chain not in seq:
                seq[chain] = []
            seq[chain] += residues
    return {k: "".join([CODES.get(r, "X") for r in v]) for k, v in seq.items()}