code: public TranscriptSequence addTranscript(AccessionID accession, int begin, int end) throws Exception {
  		if (transcriptSequenceHashMap.containsKey(accession.getID())) {
  			throw new Exception("Duplicate accesion id " + accession.getID());
  		}
  		TranscriptSequence transcriptSequence = new TranscriptSequence(this, begin, end);
  		transcriptSequence.setAccession(accession);
  		transcriptSequenceHashMap.put(accession.getID(), transcriptSequence);
  		return transcriptSequence;
  	}
docs: Add a transcription sequence to a gene which describes a ProteinSequence
  @param accession
  @param begin
  @param end
  @return transcript sequence
  @throws Exception If the accession id is already used