code: def genes_by_name(self, gene_name):
          
          gene_ids = self.gene_ids_of_gene_name(gene_name)
          return [self.gene_by_id(gene_id) for gene_id in gene_ids]
docs: Get all the unqiue genes with the given name (there might be multiple
          due to copies in the genome), return a list containing a Gene object
          for each distinct ID.