 This discovery led to the phage being used for genetic exchange and genome mapping in "E. coli", and stimulated its further study as a model organism.In the 1960s, Hideo Ikeda and Jun-ichi Tomizawa showed the phage's DNA genome to be linear and double-stranded, with redundancy at the ends.In the 1970s, Nat Sternberg characterised the Cre–"lox" site-specific recombination system, which allows the linear genome to circularise to form a plasmid after infection.