Karyograms

Karyogram is the visual representation of the karyotype, showing chromosomes arranged in standard order by size, centromere position, and banding pattern. A karyotype is the full set of chromosomes of an organism or cell; the karyogram is the photographed or drawn depiction used for analysis. In humans, somatic cells have 46 chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes (XX for females, XY for males).

To prepare, cells are cultured, arrested in metaphase using colcemid, then stained to reveal bands; G-banding is common; alternative banding methods include Q-banding, R-banding, C-banding. The chromosomes are cut out under microscope, photographed, and arranged into a karyogram by assigning numbers 1-22 and sex chromosomes.

Karyograms enable detection of aneuploidies (e.g., trisomy 21, monosomy X) and structural rearrangements (deletions, duplications, inversions, translocations). They are used in prenatal diagnosis (amniocentesis), infertility workups, and cancer cytogenetics (for example, the Philadelphia chromosome t(9;22) in chronic myeloid leukemia). Mosaicism may complicate interpretation.

Limitations and alternatives: Resolution is limited to several megabases; small copy-number variations may be missed. For higher sensitivity, techniques such as fluorescence in situ hybridization (FISH), array comparative genomic hybridization (array CGH), or sequencing-based methods are employed to detect submicroscopic changes or to analyze specific regions.