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A change in DNA can have different consequences depending on its position and the way the sequence is read. Trace the effect from bases to product before predicting phenotype.
What you'll be able to do
A base substitution replaces one base with another. An insertion adds bases and a deletion removes them. A mutation changes the DNA sequence and can arise spontaneously or be promoted by mutagenic agents; it is not the same as a temporary change in which genes are expressed.
For a coding region read in triplets, insertion or deletion of a number of bases not divisible by three shifts the reading frame downstream. Removing three bases may remove one amino-acid residue without shifting all later codons. Establish the region and reading frame before applying the term frameshift.
Because the code is degenerate, a substitution can be synonymous and leave the amino-acid sequence unchanged. A different substitution can change an amino acid or introduce a premature stop signal, shortening the polypeptide. A frameshift can alter many downstream residues and often introduces a stop signal at a different position.
A changed amino acid may affect R-group interactions, protein folding or a binding site, but its effect depends on the residue and protein. A substitution outside a critical region may have little effect on activity. “Every mutation produces a completely different protein” is therefore an unjustified claim.
A mutation in a regulatory or non-coding region can alter expression without changing a coding sequence directly. Its phenotypic effect may depend on allele interactions, the environment and the cell type. A DNA change is not automatically visible as a new trait.
In sexually reproducing organisms, a somatic mutation can affect the individual or a cell lineage without normally being passed through gametes to offspring. Germline changes can be inherited if they enter a successful gamete. Use sequence data or functional evidence to support the proposed consequence instead of assuming harmfulness from the word mutation.
Try each question before opening the worked response. Use precise biological terms, connect each cause to its effect, and check units and assumptions when interpreting data.
Common mistakes to avoid
Key takeaways
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.