Principles of Biomedical Technology (Principles of Biomedical Science)

Unit 2: Unit 2.2 Decoding a DiagnosisPBS 2.2Biotechnology Research and Experiments

Trace A Mutation to A Phenotype

Follow a single DNA base change through the mRNA codon and amino acid to the trait it causes.

Builds on (2 levels back)inferred · high confidence

DNA codes for protein: A DNA change can change a codon, which can change an amino acid in a protein.
Proteins build traits: A changed protein can change how a cell or body works: that change is the phenotype (trait).

Prerequisites are inferred: pending teacher review.

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

Trace the sickle-cell mutation one step at a time: the DNA codon GAG becomes GTG, the mRNA becomes GUG, the amino acid changes from Glu to Val, and the trait becomes sickle-shaped red blood cells.

Step 1: Start at the DNA

The normal DNA codon is GAG. The mutation changes the middle base from A to T, giving GTG.

Step 2: Go to the amino acid

That codon change makes the mRNA read GUG instead of GAG, so the amino acid changes from glutamic acid (Glu) to valine (Val).

Step 3: Reach the trait

Swapping in valine makes hemoglobin sticky, so it clumps and pulls red blood cells into a stiff sickle (crescent) shape: that shape is the phenotype.

Practice

In sickle-cell, the DNA codon GAG is changed to GTG. Using the table, which amino acid now takes the place of glutamic acid (Glu)?

Approved

Step	Normal hemoglobin	Sickle-cell change
DNA codon	GAG	GTG (the middle A is replaced by T)
mRNA codon	GAG	GUG
Amino acid	Glutamic acid (Glu)	Valine (Val)
Protein	Normal hemoglobin	Sticky hemoglobin that clumps
Trait (phenotype)	Round, flexible red blood cells	Stiff, sickle (crescent) shaped red blood cells

A.Glutamic acid (Glu)
B.Valine (Val)
C.Hemoglobin
D.A stop signal

Show the worked solution ▾

Answer: B. Valine (Val)

Step 1: Find the changed codon: The table's sickle column shows DNA GTG, which gives the mRNA codon GUG.
Step 2: Read the amino acid row: Across from GUG, the table lists valine (Val) as the amino acid.

Why it's right: The GAG-to-GTG change makes the mRNA codon GUG, and the table shows GUG codes for valine, which replaces glutamic acid.

Why the others miss:

A: Glutamic acid is the normal amino acid that the mutation replaces, not the new one.
C: Hemoglobin is the whole protein, not a single amino acid.
D: GUG codes for valine; it is not a stop signal.

Aligned to BRE: trace a point mutation · reading level ~grade 9

Where you'd see this

In Unit 2.2 Decoding a Diagnosis, this skill turns class evidence into a result another person can check.

Careers that use this

Genetic Counselor: Traces a patient's specific mutation through to the protein change that explains their condition.

Video library

Watch: Trace A Mutation to A Phenotype

Mutations (Updated)

Amoeba Sisters · 7:13

Guided notes

Fill these in as you work through the lesson.

Big idea: A mutation is a change in DNA, and you can trace it forward step by step: DNA change to codon change to amino-acid change to a changed protein to a changed trait.

Key terms: write the meaning

Mutation (a change in the DNA sequence):
Codon (three bases that code for one amino acid):
Amino acid (a building block of a protein):
Protein (the molecule that does the cell's work):
Phenotype (the visible trait that results):
Hemoglobin (the protein in red blood cells that carries oxygen):

The rule

Trace the chain in order: a change in changes a , which changes an , which changes the , which changes the (trait).

Check yourself

In sickle-cell, which single change in the DNA codon starts the whole chain?
What amino acid replaces glutamic acid (Glu), and what protein does it change?
Why does the sickle shape of the red blood cells count as the phenotype?

Work one example

Starting from DNA codon GAG changing to GTG, walk through the table to name the new amino acid and the final trait. (Answer: GTG -> mRNA GUG -> Valine -> sticky hemoglobin -> sickle-shaped red blood cells.)