@classmethod
def filtered_refgen(cls, name, description, refgen, gene_list):
    """
            Copies from a previous instance of refgen, making sure
            each gene is within gene list
        """
    self = cls.create(name, description, 'RefGen')
    for chrom in refgen.iter_chromosomes():
        self.add_chromosome(chrom)
    self.add_gene(gene_list, refgen=refgen)
    self._build_indices()
    return self
