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.

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