Figure 1. Typical changes in allelic patterns representing the two types of microsatellite alterations. A. microsatellite instability (MSI) appears as shifted allelic bands in the tumour DNA. B. loss of heterozygosity (LOH). LOH is observed as a lack of one of the allelic bands in the tumour (T) (arrow) as compared to the heterozygous alleles from leukocytes (blood).