IB Biology HL D1.3 Mutation and gene editing questions

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Type
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Question 1

Multiple choiceMedium1 mark

The diagram shows the base sequences in two cell lineages. Which interpretation correctly identifies the offspring that inherited the germ-cell mutation and the fate of the somatic-cell mutation?

C–G–A–TReference sequenceC–G–G–Tchanged baseMutated sequenceGerm-cell lineageParent germ cell/ C–G–G–TGamete/ C–G–G–TOffspring P: body cells/ C–G–G–TSomatic-cell lineageParent somatic cell/ C–G–G–TTumour cells/ C–G–G–TParent germ cell/ C–G–A–TGamete/ C–G–A–TOffspring Q: body cells/ C–G–A–T
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Answer: D. A mutation in a germ cell can pass through a gamete to the offspring, as shown by the mutated sequence in offspring P. The somatic-cell mutation is present in the tumour cells, while the separate germ-cell lineage and offspring Q retain the reference sequence.

A: swaps the offspring labels and incorrectly assigns the somatic mutation to offspring P.
B: selects Q rather than P as the offspring with the inherited germ-cell mutation.
C: reverses the somatic-cell pathway, placing its mutation in offspring Q rather than the tumour cells.
Remember: mutations in germ cells can be inherited; mutations in somatic cells can be associated with cancer but are not passed to offspring.

Question 2

Paper 2Medium16 marks

A gene in a population encodes part of a polypeptide. The table shows the coding-strand DNA sequence from a reference individual and three variants found in other individuals. The mRNA codons and their amino acids relevant to these sequences are also shown.

SequenceCoding-strand DNA, 5′→3′
ReferenceGAA CCT TGG
PGAG CCT TGG
QGAA CAT TGG
RGAA CCT TGC
mRNA codonAmino acid
GAAglutamic acid
GAGglutamic acid
CCUproline
CAUhistidine
UGGtryptophan
UGCcysteine
(a)

For P, Q and R, state the codon and nucleotide substitution. Explain why these differences are SNPs.

[4]
(b)

For each variant, state the amino acid encoded at the changed codon and whether this amino acid differs from that in the reference sequence.

[6]
(c)

Explain why the substitution in P does not change the amino acid.

[3]
(d)

A student concludes that variants Q and R must produce a different phenotype from the reference individuals. Evaluate this conclusion using the information given.

[3]

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