code: def addPartsToVSLC(
              self, vslc_id, allele1_id, allele2_id, zygosity_id=None,
              allele1_rel=None, allele2_rel=None):
          
  
          # vslc has parts allele1/allele2
  
          if allele1_id is not None:
              self.addParts(allele1_id, vslc_id, allele1_rel)
          if allele2_id is not None and allele2_id.strip() != '':
              self.addParts(allele2_id, vslc_id, allele2_rel)
  
          # figure out zygosity if it's not supplied
          if zygosity_id is None:
              if allele1_id == allele2_id:
                  zygosity_id = self.globaltt['homozygous']
              else:
                  zygosity_id = self.globaltt['heterozygous']
  
          if zygosity_id is not None:
              self.graph.addTriple(vslc_id, self.globaltt['has_zygosity'], zygosity_id)
  
          return
docs: Here we add the parts to the VSLC.  While traditionally alleles
          (reference or variant loci) are traditionally added, you can add any
          node (such as sequence_alterations for unlocated variations) to a vslc
          if they are known to be paired.  However, if a sequence_alteration's
          loci is unknown, it probably should be added directly to the GVC.
          :param vslc_id:
          :param allele1_id:
          :param allele2_id:
          :param zygosity_id:
          :param allele1_rel:
          :param allele2_rel:
          :return: