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

A)The number of individual that are presenting each of the genotype recovered are:

When only chloramphenicol 263 colonies were recovered.

Cml and pyr: 264 were recovered

Cml + Aro 290 were recovered which can synthesize aromatic amino acids.

Cml+ pyr+ Aro these are the individuals which can grow in chloramphenicol and pyrimidine and aromatic amino acid synthesis can take place.

B) The recombinant frequencies are Cml and Cml + pyr these are the recombinant individual which are chloramphenicol resistant and again in second case they are chloramphenicol resistant and can even synthesize pyrimidines.

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