Clonality in hematopoietic diseases. Chromosomal abnormalities or somatic mutations can be used as markers of clonality. Clonal defects (a pathogenic lesion or a marker indicative only of clonality) can be detected by, for example, SNP-A–based karyotyping (sensitivity problem) only if present in a significant proportion of cells. True malignant expansion of the dominant clone has to be contrasted with the clonality due to contraction of the cell compartment resulting in a recruitment of only one or a few stem cells at any given time.