You have isolated five T4 rllA mutants each of which contain

You have isolated five T4 rllA- mutants, each of which contains a deletion. You infect E. coli B hosts with pairwise combinations of these phages and test the ability of the progeny phage to subsequently lyse E. coli K hosts. The results are as follows: You then find seven point mutants (a to g) that also map to rllA. To determine the order of these mutations, you co-infect each of them with your five deletion mutants into E. coli B and test the progeny for the ability to lyse E. coli K.

Solution

* strain B — which supports the growth of all viruses thus giving the total number of viruses liberated.

* strain K — on which only wild-type viruses can grow.

rII mutants as well as wild-type T4 can infect and complete their life cycle in a strain of E. coli B. rII mutants can also infect E. coli K, but cannot complete their life cycle in strain K.

Any mutation that recombines with deletion 1 must be to the right of the deletion 1, any mutation that recombines with deletion 2 must be to the right of deletion 2, and so forth.

Let’s look at point mutation a. It recombines with deletions 2,4 and 5 but not with deletion 1,3. Therefore, it is to the right of deletions 2,4, and 5 but not to the right of deletion 1,3. We can therefore place point mutation a in the right of deletion 1 .

Point mutation b recombines with deletions 1,4 and 5 and must be to the right of them. It does not recombine with deletions 2 and 3.

Point mutation c recombines with deletions 2,4 and is to the right of 2,4 deletions,It does not recombine with deletions 1,3,5.

Point mutation d recombines with deletions 1,2 and 4 and must be to the right of them. It does not recombine with deletions 3 and 5.

Point mutation e recombines with deletions 1,5 and must be to the right of them. It does not recombine with deletions 2,3,4.

Point mutation f recombines with deletions 2,5 and must be to the right of them. It does not recombine with deletions 1,3,4.

Point mutation g recombines with deletions 1,2,5 and must be to the right of them. It does not recombine with deletions 3,4.