John Hay
John Hay Biomedical
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Genetics of Disease (Medical Interventions)
Unit 1: Unit 1.1 Pathogen ID (BLAST)MI 1.1Biotechnology Research and Experiments

Read a DNA Sequence

Use chromatogram peak evidence to read a DNA sequence accurately.

Builds on (2 levels back)inferred · high confidence
  • Control logic: Molecular results need positive and negative controls.
  • Signal interpretation: Bands, colors, curves, and E-values must be compared to a rule.

Prerequisites are inferred: pending teacher review.

Re-learn the skill with worked practice and clear examples.

Read a short DNA sequence from clean chromatogram peaks, one position at a time.

Step 1: Start at the first peak
Begin on the left edge of the chromatogram. Each main peak is one base position.
Clean chromatogram with four peaks read left to right as A C G T
Step 2: Call each peak
Use the key to turn each peak color into a letter. Write one letter for each position.
Step 3: Check the sequence
Your final sequence should have the same number of letters as the chromatogram has main peaks.
Practice

Use the chromatogram color key. The four peaks read left to right as green, blue, black, red. What DNA sequence should you write?

Approved
Clean chromatogram with four peaks read left to right as A C G T
  1. A.A C G T
  2. B.T G C A
  3. C.G C A T
  4. D.A G C T
Show the worked solution ▾

Answer: A. A C G T

  1. Step 1: Translate colors: Green is A, blue is C, black is G, and red is T.
  2. Step 2: Keep the order: Reading left to right gives A, C, G, T.

Why it's right: Green, blue, black, red translate to A C G T in order.

Why the others miss:
  • B: This does not follow the color key or the left-to-right order.
  • C: This starts with black/G even though the first peak is green/A.
  • D: The second and third calls are swapped.

Aligned to Biotechnology Research and Experiments · reading level ~grade 9

A clean chromatogram has three peaks: red, green, blue. Using the key A = green, C = blue, G = black, T = red, which sequence is correct?

Reviewed
Clean chromatogram with three peaks: red, green, blue
  1. A.T A C
  2. B.A T G
  3. C.T G A
  4. D.C A T
Show the worked solution ▾

Answer: A. T A C

  1. Step 1: Call each color: Red is T, green is A, and blue is C.
  2. Step 2: Keep the order: The peaks are read left to right, so the sequence is T A C.

Why it's right: Red, green, blue translate to T A C in left-to-right order.

Why the others miss:
  • B: This treats the colors like complements instead of direct peak calls.
  • C: Green is A, not G.
  • D: This reverses the order and changes the first call.

Aligned to Biotechnology Research and Experiments · reading level ~grade 9

Where you'd see this
  • In Unit 1.1 Pathogen ID (BLAST), this skill turns class evidence into a result another person can check.
Careers that use this
Molecular Technologist: Uses read a dna sequence to make a decision from evidence without overclaiming.
Video library
Watch: Read A DNA Sequence
Reading Chromatograms
Manuel Mendoza
Guided notes

Fill these in as you work through the lesson.

Big idea: A DNA sequencing chromatogram is a row of colored peaks you read left to right, one base per position.
Key terms: write the meaning
  • Base (one letter of DNA: A, T, C, or G):  
  • Chromatogram (a graph of colored peaks from a DNA sequencing machine):  
  • Base call (the DNA letter assigned to one peak position):  
  • Double peak (two peaks at one position that need review):  
The rule

Read a chromatogram from   to  . Use the color key to turn each peak into one DNA  .

Check yourself
  1. Which color in the key stands for each base? 
  2. Why should you read peaks from left to right instead of picking the tallest one first? 
  3. What should you do if one position has two overlapping peaks? 
Work one example

Use the color key A = green, C = blue, G = black, T = red. Peaks appear green, blue, black, red from left to right, so the DNA sequence is A C G T.