BLAST computer lab
Tue, Sep 15, 2026 · Week 4 · Genetics of Disease (Medical Interventions)
Today's goal: Use nucleotide BLAST to compare an unknown DNA sequence against a database and read the hit table.
What a finished product looks like
This is a model of the work you should turn in today. Use it to check your own: match the structure and the level of detail, do not copy it. Your data and wording should be your own.
Workflow: I pasted the unknown sequence into nucleotide BLAST at NCBI and ran the search. I annotated the screenshot to circle the top hit's organism name and percent identity.
Top hit (example values): Escherichia coli, percent identity 99 percent, E-value 2e-120.
Control run: I ran the teacher's known control sequence and it returned its expected organism at high identity, which confirms the tool and my workflow are working.
Identification statement: The unknown sample is most likely Escherichia coli, based on the top hit at 99 percent identity and a very low E-value.
| Organism (top hits) | Percent identity | E-value |
|---|---|---|
| Escherichia coli | 99% | 2e-120 |
| Shigella flexneri | 95% | 4e-90 |
| Salmonella enterica | 88% | 1e-60 |
Also due today: Upload screenshot to portfolio; bring notebook to Thursday's analysis session.
WebXam problem for today's skill
One exam-style question that uses exactly what you practiced today. Try it before you reveal the answer, then read why each choice is right or wrong.
| Organism | Percent identity | E-value |
|---|---|---|
| Organism W | 99% | 1e-130 |
| Organism X | 90% | 3e-70 |
| Organism Y | 82% | 2e-30 |
Tap an answer to see the full explanation. Nothing is recorded or graded.