Question

If a recombinant DNA bearing gene for ampicillin resistance is transferred into $E.coli$ cells and the host cells are spread on agar plates containing ampicillin, then

• A. both transformed and untransformed recipient cells will die
• B. both transformed and untransformed recipient cells will grow
• C. transformed recipient cells will grow and untransformed recipient cells will die
• D. transformed recipient cells will die and untransformed recipient cells will grow

Answer 1

The correct option is C transformed recipient cells will grow and untransformed recipient cells will die

Transformation is a process through which a piece of DNA is introduced in a host bacterium. The cells containing DNA with ampicillin resistance gene (transformed recipient cells) when introduced into the agar plate containing ampicillin will grow. This is because of the ampicillin resistant gene that will help the transformed cells resist the action of ampicillin. However, those E. coli cells which were not transformed, contained DNA without the ampicillin resistance gene (untransformed recipient cells). Due to this, those untransformed cells will not be able to resist the action of ampicillin and they will die.
The genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc., are considered useful selectable markers for $E.coli$. The normal $E.coli$ does not carry resistance against any of these antibiotics.