Auxotroph A needs methionine (met) and biotin (bio) to grow; auxotroph
   B  needs  threonine  (thr),  leucine  (leu),  and thiamine (thi); both
   require supplemented media. Lederberg and Tatum (Nobel 1958) mixed the
   two  strains and plated them on minimal medium and recovered wild-type
   prototrophs, indicating recombination had occurred.