Hi there,
Undergraduate GPA does carry more weight than graduate GPA but the entire application is reviewed at the same time. It's not an either/or situation. If I see a marginal undergraduate GPA with a A sitting there in a graduate-level Biochemistry or Physiology course, I am going to view that applicant more favorably than an applicant who took a upper division undergraduate course.
Most folks on admissions committees, like myself, have Ph.Ds in the pre-clinical sciences and know the course content of a graduate-level biochemistry or physiology course. While your total graduate GPA, if you have a graduate degree, is expected to be higher than your undergraduate degree, the OP wanted information on which courses to take to improve an undergraduate GPA in biology when there were few courses available. This person is not likely to be in a formal graduate degree program or have a formal graduate degree before they apply to medical school.
Taking a graduate course as an undergraduate is a very good thing especially if you take a course that will enhance your knowledge base in a medical school subject such as biochemistry or physiology.
njbmd 🙂