Gene mutation and its effect on the polypeptide
BiologyGeneticsAges 17–18
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Genetics
Edit one nucleotide on the template strand: substitution, insertion or deletion. The simulation re-runs transcription–translation and compares the new amino acid chain with the original, classifying the mutation as silent, missense, nonsense or frameshift, and explains why an insertion or deletion is more dangerous than a substitution. A second mode follows three Mendelian disorders – sickle-cell anaemia, β-thalassaemia and phenylketonuria – from the change in the DNA to the protein or pathway, and then to a carrier × carrier cross.
Lesson: Gene mutation
What it shows
A gene mutation changes the nucleotide sequence of DNA, and its effect depends on how it alters the codons read from mRNA. The simulation transcribes a short template strand and translates it with the standard genetic code: a substitution changes one codon and may be silent, missense or nonsense, while inserting or deleting a nucleotide shifts the reading frame. The Mendelian disorders mode shows textbook examples: the sickle-cell substitution in β-globin, a β-thalassaemia nonsense mutation and a PKU enzyme mutation, their effects on the protein or pathway, and a carrier × carrier cross with 1/4 affected children.
How to use
Keep the Mutation type on Substitute one nucleotide, move the Position through one codon and try each Nucleotide, then compare Insert one nucleotide and Delete one nucleotide at the same position; No mutation returns to the original. Press Mendelian disorders, choose a Disorder and compare the two alleles codon by codon. Choose a Genotype to see its effect (for PKU also the Diet), then press +10 children or +100 children and compare the simulated shares with 1/4, 1/2 and 1/4.
Parameters you can change
- Mutation type Substitute one nucleotide, Insert one nucleotide, Delete one nucleotide
- Position of the affected nucleotide 1–30
- Nucleotide substituted / inserted A, T, G, C
- View Edit a mutation, Mendelian disorders
- Disorder Sickle-cell anaemia, β-thalassaemia, Phenylketonuria (PKU)
Questions to explore
- Why do some substitutions, often at the third base of a codon, leave the polypeptide unchanged?
- Why does deleting a nucleotide near the start of the gene change more amino acids than deleting one near the end?
- What happens to the polypeptide when a substitution creates a stop codon partway through the gene?
