Use Controls In Identification

Use molecular-test evidence to use controls in identification 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 an unknown by comparing it to a working positive and a clean negative control.

Step 1: Confirm the controls first

The run is only valid if the positive control gives a band and the negative control gives none.

Lane	What is in it	Result
Positive control	known target DNA	band present
Negative control	no target (water)	no band
Unknown sample	patient swab	?

Step 2: Compare the unknown

If the unknown looks like the positive control, call it 'target present'; if it looks like the negative, call it 'target absent.'

Step 3: Name the limit

If a control behaves wrong, the unknown cannot be trusted yet, no matter what it shows.

Practice

Use the panel. The positive control has a band, the negative control has no band, and the unknown sample has a band. What is the best call for the unknown?

Approved

Lane	What is in it	Result
Positive control	known target DNA	band present
Negative control	no target (water)	no band
Unknown sample	patient swab	?

A.Target present, because the unknown matches the working positive control
B.Target absent, because controls do not matter
C.The run is invalid
D.Cannot tell, because the unknown was not tested

Show the worked solution ▾

Answer: A. Target present, because the unknown matches the working positive control

Step 1: Check the controls: Positive shows a band and negative shows none, so the run is valid.
Step 2: Compare the unknown: The unknown has a band like the positive control, so the target is present.

Why it's right: With valid controls and a band that matches the positive, the unknown reads as target present.

Why the others miss:

B: Controls are exactly what give the unknown meaning here.
C: Both controls behaved correctly, so the run is valid.
D: The unknown lane was tested and shows a band, so a call can be made.

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 use controls in identification to make a decision from evidence without overclaiming.

Video library

Watch: Use Controls In Identification

Positive Control vs Negative Control | Experimental Group

WInspire

Guided notes

Fill these in as you work through the lesson.

Big idea: Controls give a test its meaning: the positive control shows what a 'yes' looks like, the negative control shows what a 'no' looks like, and you read the unknown by comparing it to both.

Key terms: write the meaning

Positive control (a sample known to contain the target):
Negative control (a sample known to contain no target):
Unknown (the sample whose answer you are trying to find):
Contamination (unwanted target getting where it should not be):

The rule

Compare the unknown to the control (what a true 'yes' looks like) and the control (what a true 'no' looks like) before you call the result.

Check yourself

What result must the positive control show for the run to be trusted?
What result must the negative control show?
If the negative control shows a band, can you trust the unknown? Why or why not?

Work one example

Use the control panel. The positive control has a band, the negative control has no band, and the unknown has a band. Explain, using both controls, why you can call the unknown 'target present.'