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# Genetic tests: what each one finds

Each genetic test looks at a different scale, from whole chromosomes to single letters of DNA; the right one depends on the question asked.

Updated Nov 12, 2026

## Key facts

- Karyotype: stained chromosomes under the microscope; finds changes in number (trisomy 21) and large rearrangements of several million bases.
- FISH: a fluorescent probe for one region; quickly finds a specific deletion or translocation (22q11.2, BCR-ABL).
- Chromosomal microarray: counts DNA copies across the genome; finds small deletions and duplications a karyotype misses, but not balanced rearrangements.
- Sequencing of one gene, a gene panel, the exome (the coding parts) or the whole genome finds changes down to a single base.
- A targeted test (PCR for one known variant) is fast and cheap when the family variant or a common mutation is already known.

## In detail

- Uses: diagnosis in a patient with symptoms, predictive (presymptomatic) testing, carrier testing, prenatal diagnosis, newborn screening, pharmacogenetics, and forensic or identity testing.
- Exome and genome sequencing can return variants of uncertain significance and incidental findings; the patient should know this before testing.
- Repeat expansions (fragile X, Huntington disease) are read poorly by standard sequencing and need specific methods.
- A normal result only rules out what the test can see: a microarray misses point mutations and a sequence misses balanced translocations.
- Older mutation-scanning methods (SSCP, heteroduplex analysis, conformation-sensitive gel electrophoresis, the protein truncation test, DHPLC) searched a gene for any change before sequencing became cheap; sequencing has largely replaced them.

**Also called**
Genetic testing, Karyotype, microarray and sequencing

## Clinical notes

- Genetic testing goes with genetic counselling: what the test can and cannot show, and what a result means for relatives.
- In a child with unexplained developmental delay or several malformations, a chromosomal microarray is a usual first test, often followed by exome sequencing.
- A suspected trisomy is confirmed by karyotype, which also shows whether a translocation is involved: this changes the recurrence risk.

## Test yourself

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

## Which test detects a balanced translocation: a karyotype or a chromosomal microarray?

The karyotype. A microarray only counts copies, and a balanced translocation neither adds nor removes DNA.

## Why is a normal exome not proof that a disease is not genetic?

The exome misses non-coding regions, repeat expansions, many structural changes and balanced rearrangements.

## What is a predictive (presymptomatic) genetic test?

A test in a healthy person for a variant that will or may cause disease later, for example in a relative of someone with Huntington disease.

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## Connections

## Related conditions 4

- [Down syndrome (trisomy 21)](https://durgical.com/en/conditions/down-syndrome/)
- [Fragile X syndrome](https://durgical.com/en/conditions/fragile-x-syndrome/)
- [Huntington disease](https://durgical.com/en/conditions/huntington-disease/)
- [Hereditary breast and ovarian cancer syndrome (BRCA1/BRCA2)](https://durgical.com/en/conditions/hereditary-breast-and-ovarian-cancer-syndrome/)

## Related 6

- [FISH (fluorescence in situ hybridization)](https://durgical.com/en/biochemistry/topics/fish/)
- [DNA microarrays](https://durgical.com/en/biochemistry/topics/dna-microarrays/)
- [DNA sequencing](https://durgical.com/en/biochemistry/topics/dna-sequencing/)
- [Polymerase chain reaction (PCR)](https://durgical.com/en/biochemistry/topics/polymerase-chain-reaction/)
- [Newborn screening](https://durgical.com/en/biochemistry/topics/newborn-screening/)
- [DNA polymorphisms, linkage and DNA fingerprinting](https://durgical.com/en/biochemistry/topics/dna-polymorphisms-linkage-and-dna-fingerprinting/)

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

Sources: [What are the different types of genetic tests?: MedlinePlus Genetics](https://medlineplus.gov/genetics/understanding/testing/types/) (MedlinePlus, US National Library of Medicine, 2026); [What are whole exome sequencing and whole genome sequencing?: MedlinePlus Genetics](https://medlineplus.gov/genetics/understanding/testing/sequencing/) (MedlinePlus, US National Library of Medicine, 2026); [Genetic Consultation: MedlinePlus Genetics](https://medlineplus.gov/genetics/understanding/consult/) (MedlinePlus, US National Library of Medicine, 2026).

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