Picking a major at a UC school

I am planning to apply to the following UCs as a freshman: LA, SD, SB, Irvine, Riverside, and Davis
I plan to major in Bio Sci. Would my admission chances drop because Bio is an impacted major or does the choice of major matter at all in the admissions process? Would choosing undeclared be better for me?

Some UC’s will admit by major, some by college and some by the University. See the link for the UC matrix to see which campus(s) your 1st choice major will have the most impact on your admission. Some campuses also consider an alternate major.

http://admission.universityofcalifornia.edu/counselors/files/freshman-admission-matrix.pdf