sCl梯度 亲代15N-DNA I5N-DNA (a) Heavy (重) DNA (ON Original parent AN N-DNA 14N, 5N-DNA (中等) brid dna b)(15N-141 F一“NDNA First-generation daughter molecules 14N, 5N-DNA i 1 14N-DNA (轻) IN, I5N-DNA (中等) DNA O 14 (c) Hybrid DNA Second-generation daughter molecules