 The key ideas behind Mendel’s theory of inheritance are straightforward. In his experimental work on pea plants, Mendel observed an unusual phenomenon. He began with two ‘pure breeding’ lines, one producing plants with round seeds, the other wrinkled seeds. He then crossed these to produce the first daughter generation (the F1 generation). The F1 plants all had round seeds—the wrinkled trait had disappeared from the population. Mendel then crossed the F1 plants with each other to produce the F2 generation. Strikingly, approximately one quarter of the F2 plants had wrinkled seeds. So the wrinkled trait had made a comeback, skipping a generation.