Hershey
and
Luria
(Nobel 1969)
discovered T2 mutations that affected plaque morphology and allow detection of genetic recombination.
Mixed infections of T2 phages with mutations at two loci, r (rapid lysis - large plaques)
and h (host range - dark center plaques when grown on 2 hosts),
resulted in intergenic recombination that can be
detected by
morphology.