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How do microarrays show which genes are active in particular cells or developmental stages?
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human genome
The human genome is made up of approximately three billion base pairs of deoxyribonucleic acid (DNA). The bases of DNA are adenine (A), thymine (T), guanine (G), and cytosine (C).
Microarrays are powerful tools used in functional genomics to identify the "transcriptome"—the specific set of messenger RNA (mRNA) transcripts produced by a cell at a particular time or developmental stage.1
To determine which genes are active, researchers follow these steps:
- Preparation: mRNA is extracted from the cells of interest and converted into complementary DNA (cDNA) or cRNA, which is then labeled with a fluorescent dye.21
- Hybridization: This labeled sample is applied to a chip imprinted with thousands of ordered DNA probes, each representing a specific gene. The sample molecules bind (hybridize) to their complementary probes on the chip.21
- Detection: After washing away unbound molecules, the chip is scanned using a laser. The resulting fluorescent spots indicate which genes were expressed, as the intensity of the light corresponds to the level of mRNA present in the original sample.21
By comparing these fluorescent patterns across different samples, such as healthy versus diseased cells or different developmental stages, scientists can directly measure and compare gene expression levels.2