def tadsize_chart(genome_name):
    """
    Determine the distance threshold to build coverage tracks.
    Args:
       genome_name (string): name of the reference genome; 
                           ex: mammals, drosophila, c_elegans, s_pombe, c_crescentus
    Returns:
       dist_thresh (int): integer specifying distance threshold in basepairs
    """
    low_bound = {
        "mammals": 100000,
        "drosophila": 10000,
        "c_elegans": 1000000,
        "s_pombe": 50000,
        "c_crescentus": 30000
    }
    upp_bound = {
        "mammals": 2000000,
        "drosophila": 100000,
        "c_elegans": 2000000,
        "s_pombe": 100000,
        "c_crescentus": 400000
    }
    typ_res = {
        "mammals": 1000000,
        "drosophila": 250000,
        "c_elegans": 3000000,
        "s_pombe": 300000,
        "c_crescentus": 250000
    }
    return low_bound[genome_name], upp_bound[genome_name], typ_res[genome_name]