Determining the incidence of the hereditary form of retinoblastoma.

Retinoblastoma (Rb) is used here as the prototype of a condition which has a dominant mode of inheritance. Under the two-hit model of carcinogenesis, a germinal mutation may be followed by somatic mutation producing a tumour or tumours, in which case the carrier has relatively lower fitness. If somatic mutation does not occur, the carrier is assumed to have normal fitness, that is the Rb germinal mutation is incompletely penetrant. Formulae are given for the frequency of the Rb allele and the incidence of Rb in equilibrium as functions of the mutation rate, penetrance and fitness.