Some methods that are used to fuse foreign peptides to the surface of phage. Foreign peptides can be displayed on more than one phage coat proteins. Smaller foreign peptides are displayed in more numbers but it also depends on the type of antigen, coat protein and the phage. (a) The gene for a foreign peptide is directly fused to the minor coat-protein gene. The foreign antigen is displayed by all minor coat proteins. (b) Foreign peptide gene is attached to major coat protein gene while another copy of the gene (major coat proteins) is also present. Foreign protein is displayed on some major coat proteins. (c) Cells containing a phagemid (plasmid that have both plasmid and bacteriophage origin of replication) are infected with unchanged helper phage which then expresses the foreign peptide or protein. Foreign antigens are displayed by some coat proteins.