def rc_dna(seq):
    """
    Reverse complement the DNA sequence
    >>> assert rc_seq("TATCG") == "CGATA"
    >>> assert rc_seq("tatcg") == "cgata"
    """
    rc_hash = {
        "A": "T",
        "T": "A",
        "C": "G",
        "G": "C",
        "a": "t",
        "t": "a",
        "c": "g",
        "g": "c",
    }
    return "".join([rc_hash[s] for s in reversed(seq)])