A transformation experiment is performed with a donor strain that is resistant to four drugs: A, B, C, D. The recipient is sensitive to all four drugs. The treated recipient-cell population is divided up and plated on media containing various combinations of the drugs. The results are shown in the table below.
Drug # colonies
(a) One of the genes obviously is quite distant from the other three, which appear to be tightly (closely) linked. Which is the distant gene?
(b) What is the probably order of the three tightly linked genes?