docs: def get_chrom_for_transcript(self, transcript_id, hgnc_id):
          """ obtain the sequence for a transcript from ensembl
          """
          
          headers = {"content-type": "application/json"}
          
          self.attempt = 0
          ext = "/overlap/id/{}?feature=gene".format(transcript_id)
          r =  self.ensembl_request(ext, headers)
          
          for gene in json.loads(r):
              if gene["external_name"] == hgnc_id:
                  return gene["seq_region_name"]
          
          return None