Question 1 of 6 Fundamentals Concept

What is the difference between local and global sequence alignment?

Short answer

Global alignment compares sequences along their entire lengths. Local alignment finds the highest-scoring matching region, which is often better for shared domains or fragments.

Why

Choose the alignment objective before selecting a score. Global alignment attempts end-to-end correspondence and is most informative when sequences share similar lengths and broad homology. Local alignment extracts one or more strongly matching regions, useful when only a domain is shared or one sequence is a partial read.

As an example, a bacterial multidomain protein and a human protein might share a short catalytic domain without being comparable end to end. Gap-open, gap-extension and substitution scores influence both methods, so a high score is conditional on those choices. Inspect aligned coverage, biological context and reciprocal evidence rather than treating a local match as proof of identical protein function.

Global alignment does not force biological homology if sequences are unrelated.

Common mistakes

Calling a strong short local match evidence that two full-length proteins perform the same job

The interviewer might ask next

Which approach would you choose to compare a 60-residue peptide with a 900-residue protein?