A karyotype refers to the number and appearance (including physical structure, size, and banding pattern) of chromosomes in a cell.  To generate a karyotype, metaphase chromosomes are obtained from a population of dividing cells from virtually any cell or tissue (blood, amniotic fluid, blastomere, etc).  These chromosomes are spread onto a glass slide and stained with a dye specific for DNA that produces a characteristic banding pattern. The chromosomes are then imaged with a microscope and with the assistance of computer programs, chromosome pairs are identified and arranged in descending order of size.  Finally, the banding patterns of each chromosome are analyzed. This assists in the detection of genetic anomalies including chromosome structure defects or various aneuploidies.  For example, Trisomy 21 also commonly known as Down’s Syndrome, would be evident on a karyotype as three copies of chromosome 21 instead of only two that would be present in a euploid autosome or somatic cell.