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.

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.

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.

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.

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

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Representative model, for educational purposes only.