Past exam of the systems biology course of the University of Cambridge / 2024 / Paper 4 / Section I / 1.3

A five-base current measurement alone does not guarantee identification of one modified base in every sequence. At GGACT there is only one adenosine in the window, so attributing an established adenosine-specific modification to that A is plausible. That does not establish a universal resolution claim.

For a counterexample, consider a window containing two candidate adenosines. If modifying either position produces indistinguishable current distributions, its signal cannot identify which A changed. Overlapping windows, sequence context, calibrated modification signatures or external evidence may resolve some ambiguities, but they are extra information. This is an identifiability issue: estimating the fraction in a shifted current component is not automatically the same as identifying its molecular cause or exact position.