A geneticist wants to see if her patient has Gene X. The geneticist takes a blood sample from her patient and prepares a southern blot. How will the geneticist know if her patient possesses Gene X?

• A. A radioactive probe, which is complementary to Gene X, will bind to the membrane.
• B. A radioactive probe, which has the same sequence as Gene X, will bind to the membrane.
• C. A radioactive probe will be absent from the membrane.
• D. A southern blot cannot confirm if the patient possesses Gene X.

Answer: (A)

Verified step by step guidance

1. Understand the purpose of a Southern blot: It is a method used to detect specific DNA sequences in DNA samples. It involves transferring DNA from a gel to a membrane and then detecting the DNA with a probe.
2. Recognize the role of a probe: A probe is a fragment of DNA or RNA that is labeled with a radioactive or fluorescent tag. It is designed to be complementary to the DNA sequence of interest, in this case, Gene X.
3. Consider the binding process: If the patient possesses Gene X, the complementary probe will hybridize, or bind, to the DNA on the membrane where Gene X is present.
4. Identify the detection method: After the probe binds to the target DNA, the membrane is exposed to X-ray film or another detection method to visualize the radioactive or fluorescent signal.
5. Determine the outcome: If the probe binds and a signal is detected, it indicates the presence of Gene X in the patient's DNA. If no signal is detected, Gene X is likely absent.