Which one of the following statements gives the correct explanation for autoradiography?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Clones which have mutated genes will not appear on the photographic film
Autoradiography is used in molecular diagnosis to find a mutated gene. A probe is a single-stranded DNA or RNA tagged with a radioactive molecule. It is allowed to pair (hybridise) with its complementary DNA in a clone of cells. Where the probe pairs, the radioactivity shows up on a photographic film. A mutated gene no longer matches the probe, so the probe does not bind to it.
Option (1) Clones which have unmutated genes will not appear on the photographic film — Incorrect. A normal (unmutated) gene matches the probe. The probe binds to it, so such clones do appear on the film.
Option (2) Clones which have mutated genes will not appear on the photographic film — Correct. The probe has no complementarity with the mutated gene, so it does not bind there. With no radioactive probe attached, these clones leave no mark and do not appear on the photographic film.
Option (3) The probe used is a radioactive antibody that binds to the mutated protein — Incorrect. The probe is not an antibody. It is a single-stranded DNA or RNA tagged with a radioactive molecule, and it pairs with complementary DNA, not with a protein.
NCERT Extract:
Molecular Diagnosis – “… A single stranded DNA or RNA, tagged with a radioactive molecule (probe) is allowed to hybridise to its complementary DNA in a clone of cells followed by detection using autoradiography. The clone having the mutated gene will hence not appear on the photographic film, because the probe will not have complementarity with the mutated gene.”