T-even type phages can change their host range by recombination with gene 34 (tail fibre) or gene 23 (head).

T-even type phages recognize their cellular receptors with the tip of their long tail fibres. The gene products involved in receptor recognition are proteins 37 and 38. While screening libraries of phage K3 with a probe of gene 38 from phage T2, a class of weakly hybridizing clones was found in addition to the expected clones of gene 38 of K3. One of these clones was identified as being from gene 23 of the phage which codes for the major head subunit; another clone originated from gene 34, which codes for the proximal half of the long tail fibres. Neither gene product 23 nor 34 is involved in receptor recognition. Phages can recombine with the DNA of the gene 23 and gene 34 clones and change the host range.