---
title: "Sequence Alignment and Reading a Search Result"
description: "Two sequences are compared by scoring matches, mismatches and gaps, and the best alignment is the one with the highest total score. A database search returns hits ranked by that score with a statistic"
canonical: https://lightmysky.com/learn/science/sequence-alignment-and-reading-a-search-result-mt_jNbEMFqgZ5
source: https://lightmysky.com/learn/science/sequence-alignment-and-reading-a-search-result-mt_jNbEMFqgZ5.md
retrieved: 2026-09-12
---

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# Sequence Alignment and Reading a Search Result

Two sequences are compared by scoring matches, mismatches and gaps, and the best alignment is the one with the highest total score. A database search returns hits ranked by that score with a statistic saying how often such a match would appear by chance.

Subject: Science · Area: Genetics & Evolution · Ages 20 to 22
Page: https://lightmysky.com/learn/science/sequence-alignment-and-reading-a-search-result-mt_jNbEMFqgZ5

## Ready when they can

- Scores a short alignment by hand under a stated scheme, gaps included.
- Reads a search result and separates a strong hit from a chance one using the reported statistic.
- Explains why a short query returns weak statistics even for a perfect match.

## Lesson: Scoring alignments and judging hits

Two sequences are compared by scoring matches, mismatches, and gaps. Each column earns or loses points under a stated scheme. The best alignment is the one with the highest total score.

**Example.** Use plus 2 per match, minus 1 per mismatch, minus 2 per gap. ACGT against AGT aligns with three matches and one gap: 6 minus 2 is 4. A rival alignment scoring 1 loses to it.

A database search returns hits ranked by score, each with a statistic saying how often such a match would appear by chance. A tiny chance value marks a strong hit. A large one marks noise, even with a decent score.

**Tip.** Short queries return weak statistics even for a perfect match. Few letters can match by luck, so the math stays cautious. Lengthen the query before trusting a hit.

**Recap.** High score wins the alignment, and the chance statistic decides whether a hit matters.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Sequencing Reads and How a Genome Is Assembled](https://lightmysky.com/learn/science/sequencing-reads-and-how-a-genome-is-assembled-mt_4mUJIUAZGd)

## Opens up

- [Annotation, Orthologues and Comparative Genomics](https://lightmysky.com/learn/science/annotation-orthologues-and-comparative-genomics-mt_eBRge2bLeC)
- [Alignment Scoring: Substitution Matrices, Gap Penalties and Significance](https://lightmysky.com/learn/science/alignment-scoring-substitution-matrices-gap-penalties-and-significance-mt_k--A8iF5SC)
- [Distance and Likelihood Trees, and What Branch Support Means](https://lightmysky.com/learn/science/distance-and-likelihood-trees-and-what-branch-support-means-mt_mEO9PUEdh6)