Chapter 3 Clinical genetics/Fig 3.20.jpg

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Analysis of microsatellite ‘BAT25’ in DNA from the patient. Microsatellites are short stretches of repetitive DNA that vary in length between individual copies of the genome. Analysis of DNA extracted from blood from the individual showed two different microsatellite lengths (shaded in the figure), reflecting the two copies of the genome in a diploid individual. Analysis of DNA extracted from the tumour showed multiple different lengths of microsatellite. This occurs because loss of the sole functional copy of MLH1 causes failure of mismatch repair and the microsatellite length can change during cell division in multiple cell lineages in the tumour. The tumour is said to show ‘microsatellite instability’.