The figure 17.36 in the textbook shows the process of comparative genomic hybridization. In this technique, the DNA of a wild type and a mutant are labeled with two different fluorescent dyes which emit different wavelengths of light.
These labeled DNA molecules are added to cDNA clones which are arranged in microarrays. By comparing the signals of normal chromosomes with mutated chromosomes we can identify the different types of mutations.
The signal ratio in the bottom panel is much higher than the other panels because tandem amplification occurs in the mutant of the bottom panel. Amplification indicates that the particular sequence has been amplified or multiplied many times.