karyotipleme

Karyotipleme, also called karyotyping, is the laboratory process of visualizing an organism's chromosomes and organizing them into a karyogram to study chromosome number and structure. In humans, the normal diploid karyotype consists of 46 chromosomes: 22 autosome pairs and one pair of sex chromosomes (46,XX or 46,XY). The procedure typically begins with obtaining dividing cells from blood, bone marrow, amniotic fluid, or fetal tissue, followed by stimulation of cell division and arrest of cells in metaphase using a spindle inhibitor such as colcemid. Cells are then exposed to a hypotonic solution to swell them, fixed, and dropped onto slides to spread the chromosomes. Staining, most commonly G-banding with Giemsa after enzyme treatment, reveals characteristic light and dark bands that identify each chromosome. A photographer or scanner captures images, and a cytogeneticist arranges the chromosomes into a karyogram, pairing homologous chromosomes by size, banding pattern, and centromere position.

Karyotipleme is used to detect numerical abnormalities, such as trisomies and monosomies (for example trisomy 21 in Down syndrome) and sex-chromosome aneuploidies, as well as structural rearrangements like translocations, deletions, duplications, and inversions. Mosaicism can produce two or more karyotypes in a single individual. Common clinical applications include prenatal diagnosis, cancer cytogenetics, and investigations of infertility or congenital anomalies. Limitations include resolution constraints (generally around 5–10 Mb for G-banded chromosomes) and the need for dividing cells. Modern approaches complement karyotyping with molecular methods such as fluorescence in situ hybridization (FISH), array comparative genomic hybridization (array CGH), and sequencing to detect smaller or cryptic changes.