子一代 VNO aMejey 15N-14N 1.7101.7171.724 Density.g/cc 子二 14N 1.7101.7171.724 15N-14N Density.g/cc (a)Intact DNA(pH7) (c)DNA species present 10 10 15N- 14N 14N 15N- 14N