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