Karyotyp

Karyotyp, or karyotype, is the complete set of chromosomes of an organism or cell, including their number, size, and appearance. It is typically visualized as a karyogram, a photograph or drawing of chromosomes arranged in pairs. In humans, the diploid number is 46, organized into 22 autosomal pairs and 1 pair of sex chromosomes (XX or XY).

A karyotype reveals chromosomal structure and number, enabling detection of large-scale abnormalities such as aneuploidies (extra or missing chromosomes) and structural rearrangements such as deletions, duplications, inversions, and translocations.

Generation and analysis: Cells are cultured and arrested in metaphase; chromosomes are stained to reveal characteristic banding patterns and then photographed and ordered by size to form a karyogram. Conventional karyotyping relies on banding techniques (such as G-banding). Modern methods include fluorescent in situ hybridization (FISH) and spectral karyotyping (SKY) for targeted or whole-chromosome analysis, while array-based or sequencing approaches can detect smaller copy-number changes not visible on a standard karyotype.

Applications: Karyotyping is used in clinical cytogenetics for prenatal screening, diagnosis of congenital disorders, and cancer cytogenetics, as well as in research and evolutionary biology. A well-known example of an abnormal karyotype is trisomy 21, associated with Down syndrome.

Limitations and context: Conventional karyotyping detects relatively large chromosomal changes, typically above several million base pairs, and may miss smaller variants. It is often complemented by molecular techniques that provide higher resolution and more detailed genomic information.