One Letter, Measured

One gene, one measurement

Every mutation below is applied to the same gene, at the same place. The protein it produces is then computed, and the number of the original amino acids that survive is counted — so “worse” stops being a word and becomes a figure.

All of them at once

The same frameshift, moved along the gene

A frameshift is not one thing with one consequence. Here the identical single-base insertion is applied at every codon in turn and the damage measured each time.

Every substitution this gene could suffer

Not a sample — all of them. Every base of the coding region changed to each of the three alternatives, and the outcome classified.

Changes bigger than a base

Some mutations affect whole segments of a chromosome. Two of the five below can change a phenotype without a single gene being lost — which only makes sense once you know what Topic 6.5 showed about regulation.

Is a mutation harmful?

Pick an environment. The allele does not change between them — only the surroundings do.

Learning check

Answer these in your own words before you open the answers.

1. Define a mutation, and distinguish between a substitution and a frameshift.
2. Explain why a silent mutation is possible at all.
3. Using figures from the first tab, explain why a frameshift is more damaging than a missense substitution even though both change one base.
4. Explain why deleting three bases can be less damaging than deleting one.
5. Explain why the same frameshift is more damaging near the start of a gene than near the end.
6. A substitution occurs in the second base of a codon. State what will happen to the amino acid, and explain how you know.
7. Explain how an inversion or a translocation can change a phenotype without any gene being lost.
8. “Sickle cell is a harmful mutation.” Evaluate that statement using the data in the third tab.