docs: 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