Question

Student to attempt either option (A) or (B).
(A) 
(i) Explain how is a bacterial cell made ‘competent’ to take up recombinant DNA from the medium. 
(ii) Explain the steps of amplification of gene of interest using PCR technique. 
OR 
(B) (i) What are transgenic animals? 
(ii) Why are these animals being produced? Explain any four reasons.

Hint:

Making bacteria competent involves chemical and thermal treatments, while transgenic animals are valuable for research, medicine, and agriculture due to their modified genomes.

Answer 1

(A):
Step 1: For (i), a bacterial cell is made ‘competent’ to take up recombinant DNA by treating it with calcium chloride (CaCl$_2$) and subjecting it to a heat shock. The CaCl$_2$ makes the cell membrane permeable by interacting with the negative charges on the membrane, and the heat shock (42°C for a brief period) creates a temperature gradient that allows the DNA to enter the cell through transient pores. 
Step 2: For (ii), PCR (Polymerase Chain Reaction) amplifies a gene of interest in three steps per cycle: (1) Denaturation at 94–95°C to separate the DNA strands, (2) Annealing at 50–60°C to allow primers to bind to the target DNA, and (3) Extension at 72°C where Taq polymerase adds nucleotides to synthesize new DNA strands. This cycle repeats 25–30 times to exponentially amplify the gene. 
OR 
(B): 
Step 3: For (i), transgenic animals are organisms that have had a foreign gene (transgene) inserted into their genome using genetic engineering techniques, resulting in the expression of a new trait. 
Step 4: For (ii), transgenic animals are produced for four reasons: (1) To study gene function and regulation in a living organism, (2) To produce pharmaceuticals, like human proteins (e.g., insulin) in their milk, (3) To improve agricultural traits, such as disease resistance or growth rates in livestock, and (4) To model human diseases for research, like creating mice models for cancer studies. 
Thus, (A) explains bacterial competence and PCR steps, while (B) defines transgenic animals and provides reasons for their production.