Best major for pre MD/PhD (Pharmacology)?

I am planning on attending Truman State University and was wondering what major between Chemistry and Biology would be the best preparation for a MD/PhD program with the PhD being in Pharmacology since I want to do Pharmacogenetics research? Truman State does not offer a Biochemistry degree so which one should I major in/minor in to best prepare me for the MD/PhD (Pharmacology) and make me a competitive applicant to this program (hopefully at the University of Missouri-Columbia)? Thanks.