3 You have coinfected E coli with two strains of T4 phage On

3. You have co-infected E. coli with two strains of T4 phage. One is minute (m), rapid lysis (r) and turbid (tu). The other is wildtype for these genes. The products of this infection are plated and classified for each phenotype, with the following results: m r tu 3467 + + + 3729 m r + 853 m + tu 162 m + + 520 + r tu 474 + r + 172 + + tu 965 a. Determine recombination frequencies for each pair of genes. b. What gene order best explains these results? c. What are the distances between the genes in terms of recombination frequencies?

Solution

(1) First, try to know the parental genotype

Parent 1: + + +

Parent 2: m r tu

Now to know the distance between genes, we need to know the recombinant progeny

Distance between m and r

Recombinant progeny

Number

m + tu   

162

m + +

520

+ r tu     

474

+ r +      

172

Total      

1328

The map distance between m and r is Recombination frequency= (Number of recombinants/Total progeny)x100=1328/10,342x100 = 12.8 m.u.

Recombinant progeny

Number

m r +

853

m + tu

162

+ r +

172

+ + tu

965

Total

2152

Using the same approach, the r–tu distance is Recombination frequency= (Number of recombinants/Total progeny)x100 =(2152)/10,342x100 = 20.8 m.u

Recombinant progeny

Number

m r +

853

m + +

520

+ r tu

474

+ + tu

965

total

2812

Using the same approach, the m -tu distance is Recombination frequency= (Number of recombinants/Total progeny)x100 =(2812)/10,342x100 = 27.2 m.u.

b. As the genes m and tu are the farthest apart, you can easily predict the gene order m r tu

c. m--------12.8 m.u---------r---------------------20.8 m.u--------------------------tu