Semi-conservative DNA replication in first generation

Steps:

• Bacteria start with fully heavy DNA (both strands N-15 labeled).
• In light medium (N-14), replication produces two hybrid molecules per original: each with one heavy strand and one new light strand.
• All DNA molecules are hybrid (100%), as no fully light DNA forms yet.
• Total strands double: half remain heavy, half are new light (50% light strands).

Why C is correct:

• C matches semi-conservative model: 50% of strands are light (newly synthesized), and 100% of molecules are hybrid (one heavy, one light strand each).

Why the others are wrong:

• A: Understates light strands (not 25%) and hybrids (not 50%).
• B: Overstates hybrid percentage relative to C's accurate pairing (assuming C specifies correctly).
• D: Overstates light strands (not 75%) while hybrids are correct at 100%.

Final answer: C