Some gene mutations change the nature of all base triplets downstream from the mutation (frame shift)
Adding or deleting a base shifts every codon after that point. This scrambles the amino acid sequence from that position onwards.
Real World
Tay-Sachs disease is caused by a four-base insertion in the HEXA gene, creating a frame shift that produces a non-functional enzyme unable to break down fatty substances in nerve cells.
Exam Focus
Always state that additions or deletions cause frame shifts — substitutions do not — and explain every downstream codon is affected.
Evaluation Scaffold
A four-step framework for high-quality evaluation. Use this for 'assess', 'evaluate', and 'to what extent' questions.
How well did you know this?