In another embodiment {HEAD ~ the mutagen} is {TAIL ~ γ irradation}, ultraviolet irradiation, or X irradiation 
is
In another embodiment { HEAD ~ the mutagen } is { TAIL ~ γ irradation } , ultraviolet irradiation , or X irradiation
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH