When a position in the compared sequences is occupied by {HEAD ~ the same nucleotide base} or {TAIL ~ amino acid}, then the molecules are homologous, or identical, at that position 
When a position in the compared sequences is occupied by { HEAD ~ the same nucleotide base } or { TAIL ~ amino acid } , then the molecules are homologous , or identical , at that position
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH