def get_unresolved(aln_df):
    """Get a list of residue numbers (in the original sequence's numbering) that are unresolved

    Args:
        aln_df (DataFrame): Alignment DataFrame

    Returns:
        list: Residue numbers that are mutated

    """
    unresolved_df = aln_df[aln_df['type'] == 'unresolved']
    unresolved = []
    if not unresolved_df.empty:
        unresolved_df['id_a_pos'] = unresolved_df['id_a_pos'].astype(int)
        unresolved = unresolved_df.id_a_pos.tolist()
    return unresolved