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[Biochemistry](https://durgical.com/en/biochemistry/) · Topic

# DNA microarrays

A microarray is a chip with thousands of DNA probes that measures the expression of many genes at once or looks for gains and losses of genetic material.

Updated 2026-11-01

## Key facts

- Thousands to millions of known-sequence probes fixed on a slide; the fluorescently labelled sample hybridises and a scanner reads each spot.
- Expression microarray: compares mRNA (as cDNA) from two samples, e.g. tumour versus normal tissue.
- Chromosomal microarray (CMA or aCGH): detects copy-number variants (microdeletions and duplications) across the genome.
- SNP arrays: genotype hundreds of thousands of polymorphisms; they also show loss of heterozygosity and uniparental disomy.
- It misses balanced translocations and new point mutations (karyotype or sequencing are needed for those).

## In detail

- In aCGH the patient's and a reference DNA are labelled with different colours; the fluorescence ratio at each probe shows gain or loss.
- CMA is the recommended first test in children with intellectual disability, autism or multiple malformations without a clear cause.
- Expression profiles classify tumours and estimate prognosis (expression signatures in breast cancer).
- RNA sequencing (RNA-seq) has been replacing expression arrays in research.

**Also called**
Microarrays, DNA chips, CMA

## Clinical notes

- It detects microdeletion syndromes such as 22q11.2, Williams (7q11.23) or Prader-Willi/Angelman (15q11-q13, with methylation testing).
- SNP arrays underpin ancestry tests and genome-wide association studies (GWAS).

## Related

- [FISH (fluorescence in situ hybridization)](https://durgical.com/en/biochemistry/topics/fish/)
- [DNA sequencing](https://durgical.com/en/biochemistry/topics/dna-sequencing/)
- [Southern, Northern and Western blots](https://durgical.com/en/biochemistry/topics/southern-northern-and-western-blots/)
- [Polymerase chain reaction (PCR)](https://durgical.com/en/biochemistry/topics/polymerase-chain-reaction/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which change does a chromosomal microarray detect, and which does it miss?

It detects gains and losses (copy-number variants); it misses balanced translocations.

## What is the first genetic test in a child with unexplained intellectual disability?

Chromosomal microarray (CMA), together with fragile X testing.

## What does an expression microarray measure?

The relative amount of mRNA from thousands of genes at once, comparing two samples.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [DNA Microarray Technology Fact Sheet](https://www.genome.gov/about-genomics/fact-sheets/DNA-Microarray-Technology) (National Human Genome Research Institute (NHGRI), 2026); [Microarray Technology](https://www.genome.gov/genetics-glossary/Microarray-Technology) (National Human Genome Research Institute (NHGRI), 2026); [What are the different types of genetic tests?: MedlinePlus Genetics](https://medlineplus.gov/genetics/understanding/testing/types/) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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