The human retinoblastoma gene (RB1) is imprinted; the mouse Rb1 gene is not. Imprinted expression of RB1 is due to differential methylation of a CpG island (CpG85). which is located in the pseudogene PPP1R26P1 in intron 2 of RB1. CpG85 serves as promoter for an alternative RB1 transcript. https://www.learningepistemology.com/product-category/brow-stamp/