The pictorial illustration can be explained in 3 steps.
Step 1. Chromosomes contain many regions with repeated DNA sequences that do not code for proteins. These vary from 12 repeats between genes A and B, while the second sample has 9 repeats between the same genes.
Step 2. Restriction enzymes are used to cut the DNA into fragments containing genes and repeats. Note that the repeat fragments from these two samples are of different lengths.
Step 3. The restriction fragments are separated according to size using gel electrophoresis. The DNA fragments containing repeats are then labeled using radioactive probes. This labeling produces a series of bands–the DNA fingerprint.