Final answer:
A mutation in a mismatch repair gene significantly increases the risk of colon cancer originating from normal epithelium, as it leads to an accumulation of mutations and potential uncontrolled cell division.
Step-by-step explanation:
The effect of a mismatch repair gene mutation on colon cancer that arises from normal epithelium is an increase in the risk of colon cancer. Mismatch repair enzymes play a critical role in fixing errors that occur during DNA replication. A mutation in these enzymes can lead to an accumulation of further mutations in somatic cells, and this escalation of unchecked errors can result in uncontrolled cell division, which is a characteristic of cancer.
If many mutations accumulate due to the failure of such repair mechanisms, this can manifest as cancer, including colon cancer. In germ cells, such mutations could also be passed on to the next generation, potentially predisposing them to certain genetic conditions or cancers. Thus, a mutation in mismatch repair genes significantly increases the likelihood of cancerous growths originating from otherwise normal epithelium in the colon.