Karyotype

Clinical significance
Karyotype analysis can show chromosomal abnormalities, both numerical (such as trisomies and monosomies) and structural (translocations, deletions and inversions).
Cells taken from peripheral blood, amniotic fluid or chorionic villi are first cultured in vitro, then stopped during division, and the chromosomes are stained with substances that bind selectively to certain regions, producing a characteristic Q, G or R banding pattern depending on the staining technique used. The next step is examination under the microscope: the chromosomes are counted, analysed and photographed. They are then paired according to size, position of the centromere (the constriction of the chromosome) and banding pattern. With this test it is possible, for example, to diagnose with certainty Down’s syndrome (trisomy 21), the most common chromosomal abnormality (1 in 700), or to detect structural abnormalities caused by chromosome breaks followed by rearrangements, which can cause early miscarriages or lead, in offspring, to the loss of genetic material that can cause various conditions.