Read the following passage and answer the questions that follow :
We know that plasmids and bacteriophages are the most commonly used vectors in biotechnology experiments. If we can link an alien piece of DNA to the plasmid DNA, the alien DNA can be multiplied equal to the copy number of the plasmid. Engineered vectors are used these days. Study the diagram of the E. coli cloning vector pBR322 and answer the questions that follow :
(a) Why are plasmids and bacteriophages used as cloning vectors ?
Show Hint
They replicate independently in the host and give high copy numbers.
Step 1: Recall what a cloning vector must do:
A cloning vector carries an alien DNA piece into a host cell and makes many copies of it.
For this the vector must be able to replicate inside the host.
Step 2: Plasmids:
Plasmids are small circular DNA molecules in bacteria. They replicate on their own, independent of the chromosomal DNA.
They often occur in many copies per cell, so the linked alien DNA is multiplied as many times.
Step 3: Bacteriophages:
Bacteriophages infect bacteria and make a very large number of copies of their genome inside the host cell.
So alien DNA joined to the phage genome is also multiplied to a high copy number.
Final Answer:
Plasmids and bacteriophages replicate independently inside the host and reach a high copy number, so they multiply the linked alien DNA.
