A plant scientist investigates which genes are upregulated during tomato fruit ripening. She extracts mRNA from both ripe and unripe tomato fruits, then uses reverse transcriptase to produce cDNA from each sample. The cDNA from ripe fruits is labelled with a red fluorescent dye, and the cDNA from unripe fruits is labelled with a green fluorescent dye. The two labelled cDNA samples are mixed and applied to a microarray slide that contains immobilised DNA probes corresponding to thousands of tomato genes. After hybridisation and washing, the slide is scanned to detect fluorescence at each probe spot.
Explain how this microarray experiment detects differences in gene expression between ripe and unripe tomatoes, and how the results allow identification of genes that are upregulated during ripening.