Why is it necessary to utilize probes for labeling particular dna sequences? how is this process accomplished?

importance of a probe
in hybridization process, molecular biologist label a short fragment of DNA or RNA, usually 10-1000 bases long tagged with a radioactive or fluorescent molecules. this fragment is usually referred to as hybridization probe.probe  important both in southern and northern blotting processed because it is  used to identify a certain sequence of DNA or RNA in a pool several sequences that have been obtained using nuclease.

process of labeling DNA sequence with a probe
after the DNA strand has been cut into several fragments using enzyme DNA nuclease, the fragments are separated using gel electrophoresis and then denatured using hcl to obtain strands. the single strand are then transferred to nylon membrane that has positive charge. the next step is where probes come in. to detect the DNA sequence of interest the nylon membrane is treated with solution containing tagged probes. since the probes have complementary sequence to the target sequence, it bind to that DNA sequence and detected later using X-ray film.     
  

The type of rock she find is a sediment rock