Safety, privacy and evidence boundary
Use paper/digital molecular models and fictional DNA sequences. No biological samples, genetic testing, ancestry inference, or personal genomic data are required. Molecular models are representations and should not be treated as photographs of atoms.
Explicit science instruction
In double-stranded DNA, base pairing implies approximately equal molar amounts of A and T and of G and C. Therefore A + T + G + C = 100%, A≈T, G≈C for a double-stranded sample.
These relationships reveal composition, not sequence. Two DNA molecules can have identical base percentages and entirely different information.
Worked example with reasoning
If A = 30%, then T ≈ 30%. The remaining 40% is G + C, so G ≈20% and C≈20%. If G=18%, C≈18%, leaving 64% for A+T, so A≈32%, T≈32%.
Guided question
Why can't 30% A tell you where any adenine occurs in the sequence?
Independent work
- Solve four composition problems.
- Explain assumptions.
- Create two different 10-base sequences with identical composition.
- State what composition cannot reveal.
Misconception check
Chargaff-style equality is a compositional consequence of complementary double-stranded pairing, not a complete description of DNA structure or sequence.
Formative understanding check
If C=24%, what is G and what remains for A+T?
Worked response
G≈24%; A+T≈52%, so each is ≈26% under the model.
Open-book formative practice only; not an official mastery attempt or grade.
Mentor evidence conference
Ask Archaemenes to challenge the model, quantitative reasoning, and limits without inferring personal genetic or medical information.
Open ArchaemenesTeacher guidance
Foundation: use a 100% balance table. Core: calculate and state assumptions. Extended: analyze single-stranded exceptions and measurement uncertainty.
Preserve learning evidence
Keep the model, data interpretation, correction note, and limitation in the matching Week 23 evidence field.