A replacement vector was used to disrupt exons 1 and 2 of the Apoc1 gene by replacing them with a 2 kb hygromycin B-resistance gene. The vector was transfected into a heterozygous Apoe-deficient E14 ES cell line. Mice produced from the doubly targeted ES cells disrupted alleles of both Apoe and Apoc1. (J:22858, J:28261)