Given below are the steps carried out to construct a recombinant DNA. Which one of the following gives the correct sequence of these steps ?

(i) Isolation of genetic material

(ii) Insertion of recombinant DNA in the host cell / organism

(iii) Obtaining the foreign gene product

(iv) Amplification of gene of interest

(v) Downstream processing

The correct option is (i) → (iv) → (ii) → (iii) → (v).

Recombinant DNA technology (genetic engineering) involves a series of sequential steps to isolate, modify, amplify, and express a gene of interest in a host organism, followed by the recovery of the product. The step-by-step logical sequence is explained below:

1. Isolation of genetic material (Step i):
Before any manipulation can occur, the source DNA containing the gene of interest must be extracted and isolated in its pure form, free from other macromolecules like proteins, RNA, and lipids.

2. Amplification of gene of interest (Step iv):
Once the DNA is isolated and cleaved using restriction enzymes, the specific gene of interest is amplified to make multiple copies. This is typically achieved using Polymerase Chain Reaction (PCR), ensuring there is a sufficient quantity of the gene for insertion into a vector.

3. Insertion of recombinant DNA in the host cell / organism (Step ii):
The amplified gene of interest is ligated into a suitable vector (like a plasmid) to construct the recombinant DNA. This recombinant DNA molecule is then introduced or transferred into a competent host cell (such as E. coli or yeast) so it can replicate and express.

4. Obtaining the foreign gene product (Step iii):
After the host cells take up the recombinant DNA, they are cultured under optimal laboratory or bioreactor conditions to allow the foreign gene to express its encoded protein (the foreign gene product).

5. Downstream processing (Step v):
The final stage involves the separation, purification, formulation, and quality control testing of the expressed protein product from the culture medium before it is packaged and marketed.

Hence, the correct chronological sequence of these steps is (i) → (iv) → (ii) → (iii) → (v).