A certain recessive mutation that affects tomato is detected in 1 out of every 20,000 individuals. Two tomato plants are selected that do not show the mutation, but among whose descendants there are plants that do. If two of these descendants cross each other, which do not have the mutation: a) With what probability will the individuals of the offspring show the mutation? b) If 4 plants are randomly selected, what is the probability that only one of them has the mutation? c) Also selecting four plants at random, what is the probability that at least one of the plants does not show the mutation