What is the theoretical maximum data density per base?

• A. About 2 bits per base.
• B. About 4 bits per base.
• C. About 1 bit per base.
• D. About 3 bits per base.

Answer: (A)

The main idea here is information per symbol: with four possible DNA bases (A, C, G, T), you have four equally likely states. The amount of information each symbol can carry is log2 of the number of states, which is log2(4) = 2 bits. So the theoretical maximum data density per base is about 2 bits.

Why not more? To get 3 or 4 bits per base you’d need at least 8 or 16 distinct symbols, which isn’t possible with standard bases. One bit per base would mean only two states, which underutilizes the four-base system. In practice, real systems also face errors and other overhead that reduce usable density, but with the four-base alphabet, 2 bits per base is the ceiling.