For the imprinted gene Rb, allele mutations from different parents have different effects on tumor susceptibility in hereditary retinoblastoma: if the mutation is of paternal origin, the offspring has a 12% chance of developing retinoblastoma, whereas when the mutation is of maternal origin, the offspring have a 75% chance of developing retinoblastoma (16, 153). Here, RB1 is linked to retinoblastoma.