**Question:** Hereditary retinoblastomas develop the following chromosomal deletion:

A. Chromosome 11p13
B. Chromosome 13q14
C. Chromosome 3p26.3
D. Chromosome 6p25

**Core Concept:**

Hereditary retinoblastoma is a rare, inherited cancer affecting the retina (the light-sensitive tissue in the back of the eye). The disease is caused by mutations in either the RB1 gene on chromosome 13q14 (in about 90% of cases) or the RB1 gene on chromosome 11p13 (in about 5% of cases). The genes on chromosomes 6p25 and 3p26.3 are involved in other diseases and are not directly related to retinoblastoma.

**Why the Correct Answer is Right:**

The correct answer is chromosomes 13q14 and 11p13 because these are the locations of the RB1 gene, which is mutated in the majority of hereditary retinoblastoma cases. The RB1 gene is known to be responsible for regulating cell growth and preventing cancer. Mutations in this gene can lead to uncontrolled cell growth and the development of retinoblastoma tumors.

**Why Each Wrong Option is Incorrect:**

A. Chromosome 11p13 is a correct answer because it contains the RB1 gene that, when mutated, leads to retinoblastoma in about 5% of cases. Mutations in this chromosome are responsible for the development of retinoblastoma in these patients.

B. Chromosome 13q14 is also a correct answer as it contains the RB1 gene, responsible for retinoblastoma in about 90% of cases.

C. Chromosome 6p25 and 3p26.3 are incorrect answers since they are involved in other diseases, not retinoblastoma. Mutations in these chromosomes are responsible for other genetic disorders, not the development of retinoblastoma.

**Clinical Pearl:**

Understanding the location of the RB1 gene on chromosomes 13q14 and 11p13 is crucial for diagnosing hereditary retinoblastoma cases. This knowledge helps in identifying patients who may require genetic counseling and prophylactic enucleation (removal of the affected eye) to prevent the disease from spreading to the other eye in children with affected family members.