In 15% of sporadic gastric, colorectal, and endometrial tumors,
the mismatch repair (MMR) pathway was found to be defective. This
occurs due to the silencing of genes in the mismatch repair pathway
by DNA methylation. As a consequence, there is a rise in what is
termed “microsatellite instability” in cells with defective
mismatch repair pathway. This leads to other genes being affected
in these cells and cancer progression.

a. Explain the mismatch repair pathway repair
in no more than 2-3 sentences.

b. What is microsatellite instability? No more
than 2-3 sentences.