15N-15N Top Bottom 0 generation ←=1 generation ←=2 generations ←=3 generations ←=4 generations ←=0and2 nixed ←=0and4 nixed 14N-14N 15N-14N 15N.15N 15N- 15N 0 generation 1 generation 2 generations 3 generations 4 generations 0 and 2 mixed 0 and 4 mixed 15N- 14N 15N- 15N 14N- 14N Top Bottom