Adenomatous polyposis coli (APC) mutations are the most frequently identified genetic alteration in sporadic colorectal cancer (CRC) cases, and a myriad of genetically engineered Apc-mutant CRC mouse models have been developed using various genetic manipulation techniques. The advent of the CRISPR/Cas9 system has revolutionized the field of genetic engineering and facilitated the development of new genetically engineered mouse models. In this study, we aimed to develop a novel Apc knockout allele using the CRISPR/Cas9 system and evaluate the phenotypic effects of this new allele in two different mouse strains. For this purpose, exon 16 of mouse Apc gene was targeted with a single-guide RNA, and the mouse carrying an Apc frameshift mutation at codon 750 (Δ750) was chosen as the founder. The mutant FVB-Apc