Question

Explain how a cell could lose a remaining good copy of a tumor suppressor gene

Answer 1

This question can be answered with the help of an example; take the RB1 gene which is a tumor suppressor gene whose loss is critical for the development of cancer. This would tell you if you know genetics that RB1 gene is haploinsufficient meaning to produce tumors it requires both the copies of the gene to become ineffective. Now Retinoblastoma is either hereditary where individuals inherit a single defective copy of the gene and the tumor occurs when the remaining copy undergoes a somatic mutation or non-hereditary where a cell has both functional genes but are inactivated through the coincidence of 2 somatic mutations in one cell.
Two somatic mutations in a single cell are rare so the chance is less but in familial cases, a single somatic mutation can eliminate RB1 function and the tumor happens in both eyes.

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