In his early experiments Mendel took pollen from short stemmed pea plants, and put it on other short stemmed pea plants. The result, as you might expect, is that all the off spring were all short stemmed pea plants. Mendel called these true breeders, because all the offspring were the same as the parents.

He then took pollen from long stemmed pea plants, and put it on other long stemmed pea plants. What do you thing the result was? If you guessed that all the offspring would also be long stemmed, then you made the same guess as Gregor Mendel. Interestingly, this was not the result. Some of the long stemmed parent plants produced only tall offspring, as you would expect. However, some of the long stemmed pea plants also produced short stemmed offspring. How can this be?