Agilent 244K Human Genome CGH Microarray hybridization profile of chromosome 21 for the 3 patients. The size of the deletions is indicated by the blue bars. The small microdeletion in patient 1 is embedded within a profile that shows copy number gain with all the other oligonucleotides from chromosome 21 (red bar) reflecting the trisomy 21. The profile of patient 3 shows that the deflection of the log2 ratio (the green deflection from 0) is not uniform, indicating the presence of mosaicism in the cell population. On the basis of the FISH data, only 15% of the cells in patient 3 have the large (approximately 19.7 Mb) deletion and are deleted for the RUNX1 gene.