The rDNA cistron of Asclepias syriaca. Blue boxes represent genes. Thick black lines represent additional transcribed sequence. The gray and dashed lines represent non-transcribed and unassembled sequence respectively. Only partial sequences of the non-transcribed spacer (NTS) and external transcribed spacer (ETS) were able to be assembled due to repeats, so the length of the intergenic spacer (IGS) remains unknown.
Straub et al. BMC Genomics 2011 12:211 doi:10.1186/1471-2164-12-211