Two students fertilize a pair of pea plants. One plant is Rr, and the other is rr. The offspring produced by these two plants all had the dominant trait. The Punnett square showed that there was a 50 percent chance of the offspring carrying rr genes. So, the student assumes that he made an error in determining the genetic makeup of the plants. Do you think the student made an error, or is there another explanation? Explain your answer.