Leukemic cells have acquired genetic abnormalities. (A) Mouse GTG-banded karyotype of ME7a leukemic cells. Chromosomes are arranged alongside their corresponding ideograms (original magnification ×1000). (B) Comparative genomic hybridization of ME4 and ME4b DNA samples. The increase in copy number of a region of chromosome 4 (left panel) and decrease in copy number of a region of chromosome 15 (right panel) detected in ME4b leukemic cells compared with ME4 immortalized cells. Each point on the graph represents the log₂ ratio value of a single oligonucleotide probe. The shaded area and vertical line represent an aberrant region identified by the Z-score algorithm (CGH Analytics version 3.4; Agilent Technologies).