DNA sequencing basics
Open your materials, follow the steps, then turn in your work.
Explain what DNA sequencing measures, the order of bases in a sample, and what a later comparison with reference sequences adds before a read can help name an organism.
1. Open your materials
Use the materials named in the first step below. Open lesson resources.
2. Start the work
Use F1 and the supplied definitions to name the four DNA bases and the two pairing rules.
Show all 6 required steps
- Use F1 and the supplied definitions to name the four DNA bases and the two pairing rules.
- Read the short overview of how sequencing reads base order, then summarize it in two sentences.
- Use F1 to practice pairing bases and explain how base order differs from the names of the four bases.
- Look at the illustrative read on F1, write its partner strand from the pairing rules, and note that the letters alone do not show read quality.
- Explain what a later comparison with reference sequences could add, and what it still cannot guarantee.
- Write one question you have about turning a read into an identification.
Lost your place? Lost your place? You should have (1) your notes on the four bases and pairing, and (2) a two-sentence summary of how sequencing reads base order. If you are missing the summary, reread the short overview and write it, then move to writing the partner strand of the illustrative read and one line on what the read does not show.
Check your work before submitting
- You will be able to explain what DNA sequencing measures.
- You will be able to describe what a comparison with reference sequences can and cannot show.
- You will be able to write a partner strand from the pairing rules and say what an N in a read means.
3. Turn in your work
DueCheck Schoology- Hand in
- Notebook entry: four DNA bases with pairing rules, two-sentence sequencing summary, and one question for the BLAST lab.
How to submit and name your file
Submit one PDF of the entry in the September 11 Schoology assignment by 11:59 PM, unless Mr. Mendoza collected the paper entry in class; bring the notebook to Monday's BLAST lab.
In Schoology, open your course and the assignment for this lesson. Attach your file, select Submit, and check that it appears in the submission.
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How this lesson connects
Evidence and where it stops (Sept 10) → a read reports base order → Monday, a comparison with reference sequences. Order is the evidence; naming comes by comparison.
Need help? Warm-up, timing, and directions▸
💡 Big idea: A sequencing read reports the order of DNA bases in a sample; comparing that order with reference sequences is what can name an organism, and the naming still depends on the quality of the read and of the comparison.
- 0-10 minUse F1 and the supplied definitions to name the four bases and the two pairing rules
- 10-25 minRead the sequencing overview; summarize the process in two sentences in your notebook
- 25-40 minUse F1 to practice base pairing; compare the read and partner strand and explain what their order shows
- 40-55 minRead the illustrative string on F1; write its partner strand and mark where an N would mean an unresolved base
- 55-70 minExplain what Monday's comparison with reference sequences could add and what it cannot guarantee; compare with a partner
- 70-80 minWrite one open question for Monday's lab; submit the entry as one PDF unless it was collected on paper
- • When a sample from a sick patient will not grow in , a sequencer can still read the order of its DNA bases.
- • Today's example read is an illustrative teaching string, not a patient result; naming an organism is Monday's comparison, not today's entry.
- • Today you build the conceptual foundation for Monday's computer lab.
- • Exit goal: a two-sentence summary of how sequencing works plus one open question to bring to the computer lab.
- • DNA is made of four nucleotide bases: adenine (A), thymine (T), cytosine (C), and guanine (G); A pairs with T and C pairs with G, and sequencing determines their order along a strand.
- • A read is the reported order of bases for one sample. Organisms differ in their sequences, so comparing a read with reference sequences is how an organism can be identified, when the read and the references are good enough.
- • The letters alone do not show how well a strand was read; an N marks an unresolved base. A short illustrative read names no organism.
PLTW connection and today's work
Open Activity 1.1.3 Using DNA to Identify Pathogens in myPLTW and read the DNA sequencing background.
Today's stopping point: Activity 1.1.2 (Investigating an Outbreak) should be complete; sequencing summary due today.
PLTW activity titles identify the course connection. If your account will not open, use the posted materials for today and tell Mr. Mendoza. Do not mark an online activity complete unless you completed it.
Course connection
- Activity 1.1.3 Using DNA to Identify Pathogens
Use the turn-in directions at the top of this page. Do not create a second submission unless your teacher asks for one.
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Lesson resources: reading, slides, and vocabulary▸
Use the deck and optional guided notes to check your notebook entry. Submit one PDF unless your paper entry was collected in class.
Generated from this lesson's canonical data with a red-team citation check.
Explain what the evidence supports and where it stops.
A sequencing read reports the order of DNA bases in a sample; comparing that order with reference sequences is what can name an organism, and the naming still depends on the quality of the read and of the comparison.
Driving question: A sample swab from a sick patient will not grow in , but a machine can still read its DNA. What does the order of A, T, C, and G in that read tell us, and what has to happen before it can help name what is making the patient sick?
What you already know: Yesterday you explained what the outbreak evidence supports and where it stops. A read is one more piece of evidence with a stopping point of its own.
New idea: A sequencing read reports the order of DNA bases in a sample; comparing that order with reference sequences is what can name an organism, and the naming still depends on the quality of the read and of the comparison.
Visual or model: F1. F1 is a teaching string with its partner strand written from the pairing rules, not a sequencer output for the case. What it shows is order; what it cannot show is read quality or an organism's name. What to notice: Sequencing measures the order of bases. Order is the evidence; naming the organism comes later, by comparison.
- Write the four bases and the two pairing rules. Optional support: sketch a short paired stretch using F1.
- Read the illustrative string left to right and write its partner strand; mark where an N would mean an unresolved base.
- Write two sentences: what sequencing measures, and what a read is. Name no organism.
- Write one question for Monday's lab, then submit the entry as one PDF unless it was collected on paper.
Real biomedical example: A read from a sample that would not grow still gives an order to compare; that comparison, not the letters, is what can help name an organism. Source: DNA Sequencing Fact Sheet: what is DNA sequencing.
What the evidence supports: F1, the pairing rules and the NHGRI fact sheet support the one product: a notebook entry with the four bases and their partners, two sentences and one question.
What it cannot prove: A short illustrative read cannot show read quality or name the organism in the case.
- • DNA base: One of the four units that spell a DNA strand: adenine (A), thymine (T), cytosine (C) and guanine (G).
- • Base pairing: A pairs with T and C pairs with G across the two strands, so one strand's order fixes the other's.
- • DNA sequencing: A method that determines the order of bases along a DNA strand.
- • Read: The order of bases a sequencer reports for one sample. The letters alone do not show how well the strand was read.
- • Unresolved base (N): A position the machine could not call as A, T, C or G. It is a gap in the read, not a fifth base and not proof the whole read is bad.
- • Reference comparison: Checking a read against known sequences. This later step, not the read by itself, is what can help name an organism.
Use it now: Write the partner strand for the first six letters of the illustrative read, AATTCG, using the pairing rules; then say in one sentence what that order is evidence of.
Go further, optional: The NHGRI fact sheet explains what sequencing is and how bases pair. Its technology and cost claims are not needed for the entry.
The four DNA bases and their pairing rules: adenine (A) with thymine (T), cytosine (C) with guanine (G). F1 shows the illustrative read with its partner strand written from those rules.
Limit: Pairing tells you the partner strand. It says nothing about which organism the read came from.
DNA sequencing determines the order of bases along a strand; a read is the reported order for one sample. That order is the evidence the later comparison uses.
Limit: The NHGRI page supports what sequencing measures and how bases pair. It is not a result for the case sample.
The letters alone do not show how well the strand was read; an N marks an unresolved base, not a fifth base. A short illustrative read names no organism. The official Activity 1.1.3 trace key and case work stay in myPLTW.
Limit: A read reports base order. The letters alone cannot show how well the strand was read, and a short illustrative read cannot name an organism; identification is a later comparison with reference data.
MI-SEQ-D · Simulated classroom evidence scenario
Your role: student writing the sequencing entry from the illustrative read
Decision: A partner reads the illustrative string off F1 and says it already names the organism in the case, because it is made of real DNA letters. Decide what your entry can say from the read alone.
- • Name the organism now, because a read written in A, T, C and G is real DNA and that alone identifies what it came from.
- • Hold the whole entry until a full-length read arrives, since twelve letters are too few to show how bases pair or what a read measures.
- • Record the base order and what sequencing measures, and leave the organism's name for Monday's comparison with reference sequences.
Response: One notebook entry: the four bases with pairing rules, two sentences on what sequencing measures and what a read is, and one question for Monday's lab, submitted as one PDF to the September 11 assignment unless the paper entry was collected in class. The choice discussion is preparation, not another submission.
Claim ceiling: A read reports base order. The letters alone cannot show how well the strand was read, and a short illustrative read cannot name an organism; identification is a later comparison with reference data.
Reason for review: A sample swab from a sick patient will not grow in ; a sequencer still returns a read. The team must say what that read supplies before anyone names a cause.
Context: A composite teaching case, not a real patient. Its whole content is what a read measures and what it leaves open.
- • Nothing grows in the dish after two days.
- • The sequencer reports the order of bases in the sample's DNA: a read.
- • On Monday the read is compared with reference sequences in the lab.
- • The read is a string of A, T, C and G, with N where a base was not resolved.
- • The letters show order. They do not show how well the strand was read.
- • No organism is named until the comparison, and the comparison depends on the read and the references.
Measurements: None are supplied here. The illustrative read on F1 is a teaching string, not this case's sequence.
Figure finding: A read exists; its order can be compared. Nothing about the cause is settled today.
Uncertainty: Read quality, the presence of a matching reference, and what a match would mean are all Monday's questions.
- • The entry names all four bases and pairs each correctly.
- • Two sentences say what sequencing measures and what a read is.
- • One question is one Monday's lab can answer.
- • One entry, one PDF or the paper copy collected in class; no second submission.
- • The illustrative read is a teaching string; no organism is named from it.
- • Claims stay inside what a read supplies: order, not read quality, not identity.
- • A plain sentence about order over a confident name
- • A question for Monday over a guess today
- • A correct pair over a longer list
Test evidence: Optional practice: cover F1 and rewrite the partner strand of the illustrative read from the pairing rules; every pair matches.
- Write the four bases and pair them.
- Optional practice: write the partner strand of the illustrative read.
- Draft the two sentences in the notes field.
- Write one question for Monday.
- Check every claim against the read; remove any name or quality claim.
- Four bases, each paired
- Two sentences: measures, read
- One question for Monday
- No claim past the read
- One PDF, unless the paper entry was collected
Students often think Students assume DNA sequencing looks at the whole cell or the shape of the organism to identify it, like matching a photo.. The trap: Sequencing reads only the order of the four bases, not shape, color, or size. That order, compared with reference sequences, is what tells organisms apart. Expecting a picture makes students distrust a correct sequence-based answer.
Four DNA bases and pairing rules:
- Adenine (A) pairs with Thymine (T).
- Cytosine (C) pairs with Guanine (G).
What sequencing measures (two sentences): DNA sequencing reads the exact order of the A, T, C, and G bases along a strand. A read is the reported order of bases for one sample; it does not by itself say how well the strand was read.
What a comparison adds (Monday): matching the read against reference sequences can point to the organism it came from, if the read is good and a matching reference exists. The letters alone name nothing.
My question for the BLAST lab: how close does a match have to be before we can trust that two sequences are from the same species?
This model shows the level of evidence and organization needed to complete: A notebook entry listing the four DNA bases and their pairing rules, a two-sentence summary of what sequencing measures, and one question to carry into the BLAST lab.
- Define the term in plain scientific language.
- Connect it to the current investigation.
- Use it accurately in a new example or contrast.
Keep the structure. Replace the question, facts, measurements, and evidence. Then recheck units, vocabulary, and whether the conclusion goes beyond the evidence.
Also due today: Submit one PDF of the entry to the September 11 Schoology assignment (Wk3 Vocabulary: DNA sequencing basics) by 11:59 PM, unless the paper entry was collected in class; bring the notebook to Monday's BLAST lab.
- CER:
- Claim, Evidence, Reasoning: make a claim, back it with evidence, explain your reasoning.
- SOP:
- Standard Operating Procedure, the exact steps to follow (especially in a lab).
- Tracker:
- Your PLTW progress log where you record completed evidence.
- myPLTW:
- The PLTW course site where you do the online activities. Find it in Clever with your Microsoft sign-in, right next to Schoology.
Practice: try a question, then check your answer▸
Claim ceiling for this check: A read reports base order. The letters alone cannot show how well the strand was read, and a short illustrative read cannot name an organism; identification is a later comparison with reference data.
A sequencer returns the illustrative read AATTCGCGGAAT. What does this read measure, and what has to happen before its order can help identify an organism?
Write an answer and pick a confidence to unlock the key.
Missed class or ready for more?▸
What today's skills lead to. These are real health-science careers this course builds toward. Tap one to see, on the US Department of Labor's O*NET site, what the job actually involves, what it pays, and how fast it is growing.
Today is individual work you can do from home: complete the same target above, then submit your Vocabulary task.
Submit one PDF of your notebook entry to the September 11 Schoology assignment, Wk3 Vocabulary: DNA sequencing basics (due September 11 at 11:59 PM). If Mr. Mendoza collected the paper entry in class, do not upload it again. Bring the notebook to Monday's BLAST lab.
Class still runs. Complete the online activity above (it's self-guided). Need the concept taught without a teacher? Use this authoritative explainer:
NHGRI DNA Sequencing Fact Sheet: what sequencing measures, how bases pairHow I will check this work
- You will be able to explain what DNA sequencing measures.
- You will be able to describe what a comparison with reference sequences can and cannot show.
- You will be able to write a partner strand from the pairing rules and say what an N in a read means.
A read reports base order. The letters alone cannot show how well the strand was read, and a short illustrative read cannot name an organism; identification is a later comparison with reference data. Use the Schoology assignment linked above to submit it.
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