While working for Dr. Strap you isolate a mutant of E. coli; this time defective

Question

While working for Dr. Strap you isolate a mutant of E. coli; this time
defective in aromatic amino acid biosynthesis (aro-). You decide to map this relative to
other markers by crossing an Hfr strain which is aro+ pyr+ cmlR strs to F- aro- pyr- cmls
strR. Note: cml is for chloramphenicol resistance and pyr is pyrimidine biosynthesis.

To kill the Hfr strain you plate the exconjugants on streptomycin. From these plates you
isolate 300 colonies and then test them on different media.
Media ---> Number of colonies
Cml only ---> 263
Cml + Pyr ---> 264
Cml + Aro ---> 290
Cml + Pyr + Aro ---> 300
a) Indicate the number of individuals that are present for each of the genotypes
recovered.
b) What are the recombinant frequencies?

Explanation / Answer

When a hfr aro+, pyr+ , cmlR , str S crossed with aro -, pvr-, cmlR. , str R

Resulting 300 colonies were fist selected on streptomycin containing medium.

Out of 300 colonies 263 were cml resistant cmlR

264 are cmlR and pyr+ hence only 264-263=01 colony contains pyr gene only along with cml resistance.

290 are cmlR and aro+ out of 300 hence 290-263= 17 colonies contain aro+ only along with the cml resistance.

All 300 contains both aro+ and pyr+ along with cml resistance.

Thus frequency of cml resistant cells are 263/300=0.876

Frequency of cmlR + pyr+= 264/300=0.867

Frequency of cmlR +, aro+= 290/300= 0.9666

Frequency of cmlR, pyr+ , aro+ = 300/300=1.00

Related Questions

Navigate

• Browse (All)
• Browse W
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.