Semi-conservative DNA replication distributes strands predictably across generations Steps:

• Generation 0: All DNA is heavy-heavy (HH); 100% heavy strands.
• Generation 1 in 14N: Each HH replicates to two hybrid (HL) molecules; 100% hybrid molecules, 50% heavy strands.
• Generation 2: Each HL replicates to one HL and one LL; results in 50% hybrid molecules (2 HL out of 4 total) and 25% heavy strands (one heavy strand per HL, across 8 total strands). Why C is correct:
• Semi-conservative replication ensures each new molecule retains one parental strand; after two generations, heavy strands comprise 25% of total strands (from hybrids only), while hybrid molecules are 50% of total. Why the others are wrong:
• A: Both percentages too low; ignores semi-conservative distribution.
• B: Swaps values; 50% applies to hybrid molecules, not heavy strands.
• D: Both too high; no fully heavy molecules remain after two generations.

Final answer: C