Figure 5. Interactions between non-genetic allelic effects and heterozygous variants can shape genetic architecture at the cellular level.

( A, B) Single-molecule mRNA in situ hybridization for the mutant ( LacZ, red) and wild-type ( Bmp4, blue) alleles in a heterozygous knockout reporter Bmp4 ^LacZ/+ mouse line. Images of the postnatal day 5 (P5) and adult mouse brain are shown and reveal a mosaic of cells that preferentially express the mutant allele (red; A’ and B’), wild-type allele (blue; A’’ and B’’), and biallelic (red and blue co-expressed; A’’’ and B’’’) cells. ( C) Monoallelic mutant allele-expressing cells might be more dysfunctional than biallelic or monoallelic wild-type allele-expressing cells for some mutations.