A simple two step experiment was performed by Lederberg
using the above two strains (strain A = met-bio-thr+leu+thi+
and strain B = met+bio+thr-leu-thi-)
to test whether or not the genes are organized into linkage group(s). In step one, a mixture of A and B was grown on a minimal medium supplemented with biotin so that both met+bio+thr+leu+thi+
as well as met+bio-thr+leu+thi+
could grow. They were designed as met+bio?thr+leu+thi+.
In step two, the colonies grown on biotin supplemented medium were tested on minimal medium (deficient for biotin) and were classified into two categories (bio+
Similar tests were performed with other supplements (threonine, leucine and thiamine) also and the results are presented in Table-12.1, which suggests linkage, because in the absence linkage, due to independent assortment 1 : 1 ratio between + and - strains for each supplement should be obtained.