True, but think about this.
The first cross between Rudy and sativa was 50%50%. Then, when back crossed to sativa again, it was 25% rudy, 75% sativa. The next cross made it 87.5% sativa, 12.5% rudy. The Next was 6.25% rudy, 93.75% sativa. So you see, by the 4th back cross, it is already almost...