karyogram

A karyogram, also called a karyotype image, is a visual representation of the chromosomes of an organism or cell. It is typically prepared from somatic cells that have been cultured, arrested in metaphase, and stained so that individual chromosomes display characteristic banding. The chromosomes are cut from microscope images and arranged in a standard format, usually ordered by size from largest to smallest and grouped into homologous pairs, with sex chromosomes shown at the end. A human karyogram normally shows 22 autosomal chromosome pairs and two sex chromosomes, for a total of 46 chromosomes in a diploid cell; the exact arrangement can differ by species.

Karyograms are used to assess chromosome number and structure. They enable detection of numerical abnormalities such as trisomies (for example, trisomy 21 in Down syndrome) or monosomies (for example monosomy X in Turner syndrome), as well as structural alterations including translocations, deletions, duplications, and inversions. They can also aid in diagnosing mosaicism, where two or more cell lines with different karyotypes coexist.

Limitations include dependence on metaphase chromosomes and limited resolution; small deletions or copy-number variations may be missed. Modern cytogenetics supplements karyograms with higher-resolution techniques such as fluorescence in situ hybridization (FISH), spectral karyotyping, and array comparative genomic hybridization (array CGH). The term ideogram is sometimes used to describe a schematic representation of a karyotype showing banding patterns rather than an actual image.