To confirm the order of the metA, aceA, and iclR genes determined from two-factor crosses, three-factor crosses were done. Given the results shown below, what is the order of these three genes?
| Donor | metA::Tn10 | iclR- | ace+ |
|---|---|---|---|
| Recipient | met+ | iclR+ | ace- |
| Selected phenotype | Recombinants | Number obtained |
|---|---|---|
| TetR | IclR- Ace+ | 300 |
| IclR- Ace- | 3 | |
| IclR+ Ace+ | 30 | |
| IclR+ Ace- | 60 |
ANSWER: The rare class of recombinants would require a double cross-over as shown in the diagram below: