What are probes in RFLP made of? HOw do they help isolate rare DNA fragments?

I can't find the answer, so can I get some help please.

In RFLP (Restriction Fragment Length Polymorphism) analysis, probes are short, single-stranded DNA sequences that are labeled with a detectable marker such as a radioactive or fluorescent molecule. These probes are used to detect specific DNA fragments of interest in a sample.

To isolate rare DNA fragments, RFLP utilizes a technique called Southern blotting. Here's how it works:

1. DNA Digestion: The DNA sample is first treated with restriction enzymes that recognize specific DNA sequences and cleave the DNA at these sites. This results in the production of DNA fragments of different lengths.

2. Gel Electrophoresis: The DNA fragments are then separated based on their size using gel electrophoresis. An electric field is applied to the gel, causing the DNA fragments to migrate through the gel matrix. Smaller fragments move faster and travel farther from the point of origin, while larger fragments move slower and remain closer to the origin.

3. Denaturation and Transfer: The DNA fragments in the gel are denatured to separate the double-stranded DNA into single strands. The separated DNA fragments are then transferred from the gel onto a solid support membrane, typically a nitrocellulose or nylon membrane. This process is called blotting.

4. Probe Hybridization: The membrane is incubated with the labeled probe solution. The probes anneal, or hybridize, to the complementary DNA fragments immobilized on the membrane. The labeled probes specifically bind to the target DNA fragments they are designed to detect.

5. Detection: After washing off any unbound probes, the presence of the labeled probe bound to the target DNA fragments is detected using a suitable method. For example, if the probe is labeled with a radioactive molecule, an X-ray film or a phosphorimager can capture and visualize the radiolabeled DNA fragments. If the probe is labeled with a fluorescent molecule, a fluorescent scanner can be used to detect and quantify the fluorescence signal.

By using a specific probe, it becomes possible to identify and isolate rare DNA fragments in a sample, even if they are present in small quantities. The probe's specificity allows it to selectively bind only to the DNA fragments that contain the target sequence, enabling their detection and subsequent isolation for further analysis.