Will growing more than one type of tomato next to each other affect the seeds of the fruit, as in change what they will produce?

I have two type of tomatoes that will be growing side by side, and I dont know either of their names. I like the small one and want to save the seeds from it for later. But if its been sitting next to the other type, will the seeds be affected and turn out to be some kind of hybrid?

Also, how far away from two tomato plants be from each other if they are different types to be sure there is no mixing?