karyotype
/ KAIR-ee-oh-type /
Imagine emptying a person's full set of chromosomes onto a table and then sorting them into neat pairs by size, lining them up from biggest to smallest like a family photo arranged by height. That organized portrait is a karyotype: a picture of all of an individual's chromosomes, counted, paired, and arranged in a standard order.
To make a karyotype, technicians catch cells at the moment of division (when chromosomes are condensed and visible), stain them so they show banding patterns, photograph them, and then digitally sort them into matched pairs. A normal human karyotype shows 23 pairs — 22 pairs of 'autosomes' plus one pair of sex chromosomes (XX in a typical female, XY in a typical male). The banding pattern acts like a barcode, so each chromosome can be identified and checked for missing, extra, or rearranged pieces.
The karyotype is one of the oldest and most direct windows into the genome's large-scale structure. It can't see single-letter changes, but it readily reveals whole-chromosome problems: an extra chromosome 21 (Down syndrome), a missing or extra sex chromosome, or large chunks that have broken off and reattached elsewhere. That makes karyotyping a workhorse in prenatal testing, diagnosing certain birth conditions, and identifying chromosome rearrangements common in leukemias.
In many cases of chronic myeloid leukemia, the karyotype shows a tell-tale 'Philadelphia chromosome' — a piece of chromosome 9 fused onto chromosome 22 — which both diagnoses the disease and points to a targeted drug.
A single mis-joined chromosome, visible in the karyotype.
A karyotype is a coarse, big-picture view: it spots whole missing/extra chromosomes and large rearrangements but is blind to small mutations — those need DNA sequencing instead.