Question

If a recombinant DNA bearing a gene for resistance to Ampicillin is transferred into E.coli cells, host cells become transformed into Ampicillin-resistant cells. What happens when these E.coli are grown on a medium containing Ampicillin?

• A. Non-transformants will grow and transformants will die
• B. Non-transformants will die and transformants will grow
• C. Both non-transformants and transformants will die
• D. Both non-transformants and transformants will grow

Hint:

Antibiotic resistance markers are commonly used to identify transformed cells in molecular biology.

Answer 1

The Correct Option is B

When recombinant DNA containing an ampicillin resistance gene is introduced into E. coli, there are two possible outcomes for the bacterial cells:

(A) Non-transformants will grow and transformants will die - Incorrect: This is the opposite of what occurs. Non-transformants lack resistance and would die on ampicillin.

(B) Non-transformants will die and transformants will grow - Correct: Only transformed E. coli (those that successfully incorporated the plasmid with the ampicillin resistance gene) will survive and grow on ampicillin-containing medium.

(C) Both non-transformants and transformants will die - Incorrect: Transformants with the resistance gene should survive.

(D) Both non-transformant and transformant will grow - Incorrect: This would only occur if ampicillin wasn't working or wasn't present in the medium.

The correct answer is (B), as this demonstrates the principle of selection where only transformed, resistant bacteria survive in the presence of ampicillin.

Answer 2

When E. coli cells are transformed with recombinant DNA containing the ampicillin resistance gene, only the transformed cells can express the resistance protein. This allows them to survive in the presence of ampicillin by neutralizing its toxic effects.

Non-transformed cells lack the resistance gene and are killed by ampicillin. Therefore:

Transformants (cells with the resistance gene) will grow.

Non-transformants (cells without the resistance gene) will die.

(A): Incorrect because non-transformants cannot grow in the presence of ampicillin.

(B): Correct because only transformants survive and grow.

(C): Incorrect because transformants survive.

(D): Incorrect because non-transformants die.