Schematic representation of mouse ankyrin-1 peptide showing sites of truncation products encoded by the ENU-generated nonsense mutation Ank1*⁸⁹⁵ (Glu → stop) and the normoblastosis (nb) mouse (Ank1^nb). While the phenotype of the heterozygous (Ank1*^895/+) mutant line on the C3H background is mild, intercross breeding of mutant mice did not yield pups homozygous for the mutant allele - suggesting an embryonic lethal phenotype. Surprisingly, when the C3H-Ank1*⁸⁹⁵ line was bred with the SvImJ/129 strain we were able to obtain viable homozygous Ank1*^895/*⁸⁹⁵ offspring from intercross of the Ank1*^895/+ 129xC3H hybrid mutant line. Homozygous Ank1*⁸⁹⁵ mice were obtained at low frequency and displayed a severe phenotype with remarkable splenomegaly. In this study we have generated a novel mouse model of hereditary spherocytosis and examined the compensatory mechanisms that permit the survival of homozygous Ank1*⁸⁹⁵ mice from embryo to adults. In addition, we determined the stability of Ank1*⁸⁹⁵ protein in homozygous mice and its effect on the assembly of RBC membrane structural complexes in the absence of full-length ankyrin-1. MRH and SM are fellows of the CIHR/HSFC Strategic Training Program in Transfusion Science at the UBC Centre for Blood Research (CBR). KMM is a Michael Smith Foundation for Health Research Scholar and CBR member. This study was supported by a group operating grant from the CIHR (FRN 74611) and fellowships from the Heart & Stroke/Richard Lewar Centre of Excellence.