Subject Experts Solutions for Exercise 2: HOTS HIGHER ORDER THINKING SKILLS

Four mutant strains of bacteria $(1-4)$ all require substance $S$ to grow (each strain is blocked at one step in the $S-$biosynthesis pathway). Four plates were prepared with minimal medium and a trace of substance $S,$ to allow a small amount of growth of mutant cells. On plate $A$, mutant cells of strain $1$ were spread over entire surface of the agar to form a thin lawn of bacteria. On plate $B$, the lawn was composed of mutant cells of strain $2,$ and so
on. On each plate, cells of each of the four mutant types were inoculated over the lawn, as indicated in the figure by the circles. Dark circles indicate excellent growth. A strain blocked at a later step in the $S$ substance metabolic pathway accumulates intermediates that can 'feed' a strain blocked at an earlier step.

What is the order of genes $(1-4)$ in the metabolic pathway for synthesis of substance $S ?$

The figure shows the restriction enzyme cutting sites $(\mathrm{R}1-\mathrm{R}3)$ in wild type $\left(n\right)$ and mutant $\left(n\right)$ gene.

If a radioactively labelled probe (that hybridizes at a sequence close to $\mathrm{R}1)$ is used for detecting the presence of $\mathrm{DNA}$ fragments after gel electrophoresis and Southern blotting, which of the following band patterns will your expect?

Note :$\mathrm{L}1:$wild type$\mathrm{DNA}, \mathrm{L}2:$ mutant $\mathrm{DNA}$

Analyse the given diagram which shows steps involved in the procedure of selecting transformed bacteria.

Identify the bacterial colony which has undergone transformation?

The nucleic acid extracted from the animal liver is loaded and run on an agarose gel. After staining, it shows the following pattern:

If the remaining sample is treated with $\mathrm{RNAse}$ and loaded in gel what result would you expect?

The basic procedure involved in the synthesis of recombinant $\mathrm{DNA}$ molecule is depicted below.

The mistake in the procedure is: