**Core Concept**
Hereditary retinoblastomas are a type of eye cancer that primarily affects children, caused by mutations in the RB1 gene. This gene acts as a tumor suppressor, regulating cell growth and division. The deletion of the RB1 gene leads to uncontrolled cell growth and tumor formation in the retina.

**Why the Correct Answer is Right**
The correct chromosomal deletion associated with hereditary retinoblastomas is the loss of the long arm of chromosome 13, specifically 13q14. This deletion involves the RB1 gene, which is a critical tumor suppressor gene. The RB1 protein regulates the cell cycle by inhibiting the E2F transcription factor, preventing excessive cell growth. The loss of the RB1 gene allows cancerous cells to proliferate, leading to retinoblastoma.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct chromosomal deletion associated with hereditary retinoblastomas.
**Option B:** This option is incorrect because it refers to a different type of cancer, such as osteosarcoma, which is associated with a different genetic mutation.
**Option C:** This option is incorrect because it is a different chromosomal deletion that is not associated with hereditary retinoblastomas.

**Clinical Pearl / High-Yield Fact**
Hereditary retinoblastomas are inherited in an autosomal dominant pattern, meaning that a single copy of the mutated gene is sufficient to increase the risk of developing the disease. This is in contrast to sporadic retinoblastomas, which occur without a family history.

**Correct Answer:** D.