Practice Problem Set #5

  1. E. coli cells were infected with two strains of T2 phage, one wild type for two plaque traits and the other doubly-mutant.  The lysate from this mixed infection experiment was plated out, with the following results:
        186 + +
        127 a +
        139 + b
         60  a b
What is the map distance between locus a and locus b?

  2. DNA extracted from wild-type Bacillus subtilis was used to transform mutant cells that are unable to synthesize the amino acids arginine (arg) or proline (pro), with the following results:  5000 pro+ arg+, 1000 pro- arg+, 500 pro+ arg-, 8000 pro- arg-.  What is the map distance between these two loci?

  3. A researcher wishes to estimate map distances between three viral loci.  He has six viral strains, each carrying at least one mutation at the object loci, a, b, and/or c.  He performs the following mixed infection experiments:

     Cross                   % completely wildtype progeny
 1) ab+ X ++c                        8.75
 2) a+c X +b+                        3.75
 3) +bc X a++                        1.25

Give the correct linkage order and map distances.

4. Donor DNA from a strain of wild-type bacteria was used to transform a bacterial strain mutant at three loci, and the results are given below:

aro+ his+ try-  148        aro+ his- try+ 2285
aro- his- try+   197        aro+ his+ try+ 5860
aro- his+ try+    11        aro histry-    111
aro- his+ try-  878

Give the map distances.

  5. A particular phage DNA molecule is radioactively labelled at its 5' ends and cleaved by EcoRI into five fragments of sizes 4.5, 2.9, 6.2, 7.4, and 8.0 kilobases.  The 6.2 and 8.0 kb fragments are found to be labelled.  When the same experiment is repeated substituting the restriction enzyme BamHI, fragments of sizes 6.0, 10.1, and 12.9 kb are obtained, with the 6.0 and 10.1 fragments labelled.  When both enzymes are used together, the fragments have sizes 1.0, 2.0, 2.9, 3.5, 6.0, 6.2, and 7.4 kb.  Draw the restriction map of this particular phage genome.

 1.) 52 mu,  2.) 23 mu,  3.) b 10 a 20 c,   4.) his  34.6  aro  4.9  try
        5.)    6.2   E   2.9  E  1.0   H   3.5  E   7.4   E  2.0   H   6.0

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