def make_gtf_url(ensembl_release, species, server=ENSEMBL_FTP_SERVER):
    """
    Returns a URL and a filename, which can be joined together.
    """
    ensembl_release, species, _ = \
        normalize_release_properties(ensembl_release, species)
    subdir = _species_subdir(
        ensembl_release,
        species=species,
        filetype="gtf",
        server=server)
    url_subdir = urllib_parse.urljoin(server, subdir)
    filename = make_gtf_filename(
        ensembl_release=ensembl_release,
        species=species)
    return join(url_subdir, filename)
Returns a URL and a filename, which can be joined together.