Safety, privacy and evidence boundary
Use paper models, public educational sequence examples, and fictional DNA. Do not perform unsupervised wet-lab amplification, collect personal DNA, upload personal genomes, or provide procedural gene-editing instructions. Privacy, consent, and dual-use risks are part of the science.
Explicit science instruction
Gel electrophoresis separates DNA fragments primarily by size through a matrix under an electric field. Smaller fragments generally migrate farther. A DNA ladder provides reference fragment sizes.
Band position estimates size; band intensity can reflect amount but depends on staining, imaging and loading. Matching bands support similarity at tested fragments, not proof of whole-genome identity.
Worked example with reasoning
A ladder has known fragments at 1,000, 700, 500 and 300 bp. An unknown band lies between 700 and 500 closer to 500. A calibration plot of migration distance versus log(fragment size) can estimate size more accurately than visual guessing.
Guided question
Why is a calibration curve stronger than simply saying “this band looks about 600 bp”?
Independent work
- Order sample fragments by migration distance.
- Estimate three sizes from a supplied ladder.
- Plot a simple calibration curve.
- State what a matching band can and cannot establish.
Misconception check
A band is not a gene “showing itself”; it represents DNA fragments of similar migration behavior under the assay.
Formative understanding check
Which generally travels farther in the same gel: 300 bp or 1,000 bp?
Worked response
The 300-bp fragment.
Open-book formative practice only; not an official mastery attempt or grade.
Mentor evidence conference
Ask Archaemenes to challenge your evidence classification, model assumptions, quantitative reasoning, and ethical boundaries.
Open ArchaemenesTeacher guidance
Foundation: use printed ladders. Core: estimate size and state uncertainty. Extended: use log-size calibration and compare resolution limits.
Preserve learning evidence
Keep models, calculations, source notes, corrections, and limitations in the matching Week 26 evidence field.