A karyotype is a snapshot of the genome; it can be used to detect extra or missing chromosomes, chromosomal rearrangements, or chromosomal breaks. Any cell that contains a nucleus can be used to make a karyotype. However, white blood cells seem to work best for human karyotypes. After the cells are cultured, they are killed by using a drug that halts mitosis—the chromosomes are then stained, observed, and a size order chart is produced.