The cells contain {HEAD ~ an effector gene} under control of a transcriptional control element that causes the gene to be expressed in relatively undifferentiated cells in {TAIL ~ the population} 
The cells contain { HEAD ~ an effector gene } under control of a transcriptional control element that causes the gene to be expressed in relatively undifferentiated cells in { TAIL ~ the population }
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL