def get_indel_seq(row):
    """Gets indel sequence
       
    Args: 
        row (pandas.Series): a Series with 'ref' and 'alt' indices
    Returns:
        indel_seq (str): inserted or deleted  sequence
    """
    if row["ref"] == "-":
        indel_seq = row["alt"]
    else:
        indel_seq = row["ref"]

    return indel_seq