For the Life Sciences program,can I change my major once in the university from Life Sciences to Genetics (Co-op)? Will they let me switch into a co-op major or will I never get into a co-op major since I mentioned a non co-op major on my university application on OUAC?

you in high school? what you select now doesnt matter. if you start off in life sci, near the end of year 1 of uni you will apply to a bunch of science programs of your choice and if you get in, you can choose which to go to. dont worry about the ouac thing, its a waste.

^I second that, as someone in a science co-op program you apply to the coop program in your second year. You apply to all other non coop programs at the end of your first year.

What you selected as a major is just for planning purposes for the school. You're not actually applying to those majors, nor are you guaranteed entrance to those majors if you accept your offer to life sciences.