Some Genetics Problems

1.

A culture of E. coli strain B is coinfected with equal numbers of a triple mutant of T4 phage, d g r, and wild type (+ + +). 1000 plaques were analyzed and their genotype were distributed as follows.
d g r 425
+ + +430
d g +3
+ + r2
d + r58
+ g +62
+ g r11
d + +9

A. What is the gene order?

B. What is the map distance between r and d?
between g and r?
between d and g?

C. In a two-point cross between the two outside loci, what map distance would have been observed?

Answers

2.

A set of six rII deletion mutants were crossed with each other in all possible combinations with the following results ( + = recombinants produced, i.e., able to grow on E.coli strain K; 0 = no recombinants).

  1 2 3 4 5 6
1 0 + 0 + + +
2   0 0 + + 0
3     0 0 + 0
4       0 0 0
5         0 +
6           0

Draw a deletion map consistent with these data.

Answer

3.

A liquid culture of E. coli strain B is coinfected with equal numbers of two rII point mutants of T4: rII-7 and rII-38. Suspensions of progeny phage are plated on both strain B (giving 1000 plaques per ml of suspension) and on strain K (giving only 5 plaques per ml of suspension). What is the number of map units between site "7" and site "38"?
Answer

4.

Various pairs of rII mutants or T4 were tested in both cis and trans positions in E. coli stain K and comparisons made as to the average number of phage particles produced per bacterium ("burst size"). One set of hypothetical results for 4 different rII mutants, r1, r2, r3, and r4, is as follows. ( + = wild type; the slash [/]separates loci on different DNA molecules.)

cis burst size trans burst size
r1r2/++ 250 r1/r2 258
r3r4/++ 245 r3/r4 252
r1r3/++ 260 r1/r3 250
r1r4/++ 270 r1/r4 0
r2r3/++ 265 r2/r3 0
r2r4/++ 240 r2/r4 270

How many cistrons are represented and which mutations are in each?

Answer

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8 March 2011