def read_bim(file_name):
    """Reads the BIM file to gather marker names.

    :param file_name: the name of the ``bim`` file.

    :type file_name: str

    :returns: a :py:class:`dict` containing the chromosomal location of each
              marker on the sexual chromosomes.

    It uses the :py:func:`encode_chr` to encode the chromosomes from ``X`` and
    ``Y`` to ``23`` and ``24``, respectively.

    """
    marker_names_chr = None
    with open(file_name, 'r') as input_file:
        marker_names_chr = dict([
            (i[1], encode_chr(i[0]))
            for i in [
                j.rstrip("\r\n").split("\t") for j in input_file.readlines()
            ] if encode_chr(i[0]) in {23, 24}
        ])
    return marker_names_chr