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. Define the 'two-hit hypothesis' for retinoblastoma.

Key Concepts

Two-Hit Hypothesis

The two-hit hypothesis, proposed by Alfred Knudson, suggests that cancer develops through a two-step process involving mutations. In the case of retinoblastoma, the first 'hit' is a hereditary mutation in one copy of the RB1 gene, which predisposes individuals to cancer. The second 'hit' is typically a somatic mutation that occurs in the other copy of the gene, leading to the loss of function and the development of tumors.

RB1 Gene

The RB1 gene encodes a protein that regulates the cell cycle and prevents excessive cell growth. Mutations in this gene can disrupt its function, leading to uncontrolled cell division and the formation of tumors. In retinoblastoma, the inheritance of one mutated RB1 allele significantly increases the risk of developing cancer, as the normal allele must also be inactivated for the disease to manifest.

Dominant Inheritance

Dominant inheritance refers to a pattern where only one mutated copy of a gene is sufficient to express a trait or disease. In the context of retinoblastoma, inheriting one mutated RB1 allele from a parent leads to a predisposition for cancer, as the individual is at a higher risk of acquiring a second mutation in the remaining normal allele, thus fulfilling the two-hit hypothesis.