How is data density defined in DNA storage and what limits it?

• A. Bits per nucleotide; constrained by physical packaging limits.
• B. Bits per nucleotide; limited by error-correcting overhead and encoding constraints, with theoretical maximum around 2 bits/base.
• C. Bits per base is fixed at 1.
• D. Density is determined solely by sequencing speed.

Answer: (B)

Data density in DNA storage is measured as bits per nucleotide. In principle, four bases give 2 bits per base, but real systems must include error-correcting codes and sequence constraints (to avoid long repeats, keep GC balance, ensure reliable synthesis and reading). This overhead reduces the net information stored per base, so the practical density is below 2 bits per base. The theoretical ceiling is around 2 bits per base when ignoring overhead, but error correction and encoding constraints are the factors that set the actual limit. Packaging or sequencing speed affect throughput or practicality, not the fundamental per-base information density.