What kind of math classes must you take to become a Biologist? What kind of math classes must you take to become a Geneticist?
I'm not a biologist, but I do know a little about math. I know there's a specialty in math called bio-stastics.
I think that course requires at least 1yr of calculus, linear algebra, mathematical probability and mathematical stasticis. I've had all of those and enjoyed each.
I'm not sure what geneticists would need, but I suspect they need probability and statistics too, at the very least.
Although Roger is probably right about the minimum requirement, the requirements are likely to vary from one school to another. Assuming that you are in your last year of high school, it would be advantageous to correspond to colleges that you are thinking of attending.
In addition, it would be very advisable to consult your high school counselor, who is likely to have more information. That person is more likely to be more able to quickly answer other questions that might arise, because s/he could match your needs to the available schools.
If the math requirement seem overwhelming, the counselor could suggest other career options involving less math that would match your interests.
I hope this helps a little more. Thanks for asking.