code: public ExonSequence removeExon(String accession) {
  		for (ExonSequence exonSequence : exonSequenceList) {
  			if (exonSequence.getAccession().getID().equals(accession)) {
  				exonSequenceList.remove(exonSequence);
  				exonSequenceHashMap.remove(accession);
  				// we now have a new gap which creates an intron
  				intronSequenceList.clear();
  				intronSequenceHashMap.clear();
  				intronAdded = false;
  				try{
  					addIntronsUsingExons();
  				} catch(Exception e){
  					logger.error("Remove Exon validate() error " + e.getMessage());
  				}
  				return exonSequence;
  			}
  		}
  		return null;
  	}
docs: Remove the exon sequence
  @param accession
  @return exon sequence