36 exam-style questions on Mutation and gene editing — topic D1.3 of Continuity and change in the IB Biology syllabus — with answers and explanations. Samples below; the full set is free with an account.
Restriction enzymes are useful in genetic engineering because they:
Answer: Cut DNA at specific base sequences
Restriction endonucleases cut DNA at specific base sequences. Staggered cuts leave single-stranded 'sticky ends' that can base-pair with complementary ends of other DNA, allowing fragments to be recombined.
In bacterial gene cloning, a plasmid is used mainly as a:
Answer: Vector carrying a gene into a cell
Plasmids are small circular DNA molecules that replicate independently in bacteria. A gene inserted into a plasmid vector can be taken up by host cells and expressed or copied along with the plasmid.
A single base is inserted near the start of a gene's coding sequence. Determine the most likely consequence for the encoded polypeptide.
Answer: A frameshift altering downstream codons
An insertion (not a multiple of three) shifts the reading frame, so every codon downstream is misread, usually producing a nonfunctional protein and often a premature stop.
A base substitution changes the codon GAA to GAG. Both code for glutamate. Classify this type of mutation.
Answer: Silent mutation
Because the amino acid is unchanged, the substitution is silent (synonymous), a direct consequence of the degeneracy of the genetic code at the third position.
The sickle cell allele results from a base substitution that changes one amino acid (glutamate to valine) in the beta-globin chain. Classify this mutation.
Answer: Missense mutation
A single amino acid is changed to a different one, which defines a missense mutation; the altered haemoglobin causes red blood cells to sickle under low oxygen.
State the component of the CRISPR-Cas9 system that directs the Cas9 nuclease to a specific DNA target sequence.
Answer: A guide RNA (gRNA)
The guide RNA base-pairs with the complementary target DNA, positioning Cas9 to make a precise double-strand cut at that locus.
That was 6 of 36 Mutation and gene editing questions.
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36 Mutation and gene editing questions — free with an account. Spaced repetition, streaks and full exam simulations included.
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