During a routine examination of a 3-year-old child, the pediatrician notes that the color of the pupil is white and that the child is cross-eyed. She asks the child's father if there are any cases of retinoblastoma in the family, and when the answer is in the affirmative she calls in a pediatric ophthalmologist. The ophthalmologist knows that retinoblastoma is due to the mutation of the Rb gene (retinoblastoma gene) and that it is a recessive trait. Not all cases of retinoblastoma have a familial component. In the sporadic form of retinoblastoma, the child's normal genetic complement does not predispose the child to have retinoblastoma. If this child had the sporadic form of retinoblastoma, then
A) one copy of the Rb gene mutated
B) both copies of the Rb gene mutated
C) the patient's future children will most probably will have one mutated Rb gene
D) the patient's future children will most probably have two mutated Rb genes
E) the mutated Rb gene is known as a protooncogene

Question

Quizplus · Accepted Answer

In sporadic cases of retinoblastoma, both copies of the Rb gene are mutated, as opposed to the familial form where only one copy is mutated. Therefore, the best choice is B - both copies of the Rb gene mutated. Choices A, C, D, and E are all incorrect based on the genetic basis of sporadic retinoblastoma.

During a Routine Examination of a 3-Year-Old Child, the Pediatrician