Now a days it is possible to detect the mutated gene causing cancer by allowing radioactive probe to hybridise its complimentary DNA in a clone of cells, followed by its detection using autoradiography because :

The correct option is: mutated gene does not appear on a photographic film as the probe has no complimentarity with it.

Step-by-Step Explanation:

1. Concept of Radioactive Probes and Hybridization:
In biotechnology and diagnostics, a single-stranded DNA or RNA molecule tagged with a radioactive molecule (called a probe) is used to detect the presence of a complementary sequence in a clone of cells. Under normal conditions, the radioactive probe will hybridize (bind) to its complementary target DNA sequence because the base-pairing matches perfectly.

2. Detection via Autoradiography:
Once hybridization occurs, autoradiography is performed. When the photographic film is exposed, the radioactive labels on the hybridized probes emit radiation that leaves a visible spot or band on the film. Therefore, cells containing the normal gene will show up on the photographic film because the probe hybridizes with it successfully.

3. Effect of Mutation:
When a gene undergoes a mutation, its nucleotide sequence changes. Because of this alteration, the radioactive probe (which is designed specifically to match the normal, non-mutated gene sequence) will no longer have complementarity with the mutated gene.

4. Resulting Observation:
Due to the lack of complementarity, the probe cannot hybridize with the mutated gene. Consequently, during the washing step of the procedure, any unbound probe is washed away. Since there is no radioactive probe bound to the mutated gene, no radioactive signal is emitted from that spot. Thus, the mutated gene does not appear on the photographic film.