Homology or identity can be determined by comparing a position in each sequence which may be aligned for {HEAD ~ purposes} of {TAIL ~ comparison} 
of
Homology or identity can be determined by comparing a position in each sequence which may be aligned for { HEAD ~ purposes } of { TAIL ~ comparison }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL