There are two separate sets of approval that you need to get in order for a transfer course to count toward the Biology major requirements.
The guidelines for transferring courses to Stanford are located on the Registrar's Office webpage. Please be sure to follow these instructions; without doing so, you run the risk of not having your courses transferred.
The first thing to do is check the "Pre-Approved" binder in the Student Services Office (Gilbert 108). If the course you want to take is in there, you are done! If not, you will need to fill out a Transfer Credit Evaluation Form. Complete this form, attach a syllabus and/or course description, and return it to the Biology Student Services Office. The undergraduate staff advisor will work with the appropriate department to have the course evaluated for equivalency.