For the retinal cancer retinoblastoma, the inheritance of one mutated copy of RB1 from one of the parents is often referred to as a mutation that produces a 'dominant predisposition to cancer.' This means that the first mutation does not produce cancer but makes it very likely that cancer will develop.

Using RB1⁺ for the normal wild-type allele and RB1⁻ for the mutant allele, identify the genotype of a cell in a retinoblastoma tumor.

Verified step by step guidance

1. <span>Step 1: Understand the genetic basis of retinoblastoma. Retinoblastoma is a type of cancer that is often associated with mutations in the RB1 gene. Individuals with retinoblastoma typically inherit one mutated allele (RB1⁻) from a parent, which predisposes them to cancer.</span>
2. <span>Step 2: Recognize the concept of 'two-hit hypothesis.' According to this hypothesis, both alleles of a tumor suppressor gene like RB1 must be inactivated for cancer to develop. In hereditary retinoblastoma, individuals are born with one mutated allele (RB1⁻) and one normal allele (RB1⁺).</span>
3. <span>Step 3: Determine the genotype of a cell in a retinoblastoma tumor. For a tumor to form, the second allele must also become mutated. Therefore, the genotype of a cell in a retinoblastoma tumor would be RB1⁻/RB1⁻, indicating that both alleles are mutated.</span>
4. <span>Step 4: Consider the implications of this genotype. The loss of function of both RB1 alleles leads to uncontrolled cell division, which is a hallmark of cancer.</span>
5. <span>Step 5: Summarize the genetic change. In retinoblastoma tumors, the genotype RB1⁻/RB1⁻ reflects the complete loss of functional RB1 protein, which is crucial for regulating the cell cycle and preventing tumor formation.</span>

Key Concepts

Dominant Inheritance

Dominant inheritance refers to a pattern where a single copy of a mutated gene is sufficient to express a trait or condition. In the case of retinoblastoma, inheriting one mutated RB1 gene (RB1⁻) from a parent increases the likelihood of developing cancer, even though the individual may not show symptoms until a second mutation occurs.

RB1 Gene Function

The RB1 gene encodes a protein that is crucial for regulating the cell cycle and preventing uncontrolled cell growth. When this gene is mutated, its ability to control cell division is compromised, leading to an increased risk of tumor formation, particularly in retinal cells, which can result in retinoblastoma.

Genotype of Tumor Cells

In retinoblastoma tumors, the genotype typically reflects the loss of function of both RB1 alleles. A common genotype for tumor cells would be RB1⁻/RB1⁻, indicating that both copies of the RB1 gene are mutated, which is necessary for the development of the cancerous phenotype in the retinal cells.