import re


def _build_alt_tx_res(id_list):
    """Create regular expressions to find alternative transcripts.

    Matches alternative transcripts of base.1 of the form:
        base.1a
        base.1.1
        base.1a.1
    """
    final_list = []
    for cur_id in id_list:
        match_re = re.compile(r"^" + cur_id + r"([a-z]+|\.\d+)(\.\d+)?$")
        final_list.append((cur_id, match_re))
    return final_list