The short answer
Punnett-square reasoning and the probability skills behind Section III genetics.
Written and checked by GAMSAT tutors — not AI-generated.
Try the reasoning style
We treat forgetting as a failure — a lapse to be patched with reminders and records. Yet a mind that kept everything could not think; it would drown in the undifferentiated noise of every moment it had ever lived. To forget is not so much to lose information as to decide, mostly without our noticing, what was never worth keeping.
The author's argument relies most directly on which unstated assumption?
Pick an option to see how the tutor reasons to the answer — not just whether you were right.
Not quite — the answer is B.
Work backwards from the conclusion: a mind that ‘kept everything’ supposedly ‘could not think.’ That only follows if thinking means leaving most of experience out — so B is the premise the argument quietly rests on. A raises reliability, which the passage never weighs; C contradicts ‘mostly without our noticing’; D smuggles in a claim about intellect the passage never makes. The question rewards finding the hidden premise, not recalling a fact.
Genetics questions reward clear probability reasoning, not memorised pedigrees. Master the monohybrid cross and you can handle most of what Section III throws at you.
The vocabulary that unlocks it
Genotype is the allele pair (e.g. Aa); phenotype is the trait you see. A dominant allele (A) masks a recessive one (a) — so only aa shows the recessive trait.
Worked monohybrid cross
Two heterozygous parents (Aa × Aa) have a child. What's the chance the child shows the recessive trait?
Check yourself
In a cross Aa × Aa, what fraction of the offspring are expected to be carriers (heterozygous, Aa)?
Key takeaways
- Genotype = the alleles (Aa); phenotype = the visible trait.
- A recessive trait shows only when both alleles are recessive (aa).
- Aa × Aa gives a 1:2:1 genotype ratio and a 3:1 phenotype ratio.
- Treat each parent's allele as an independent 50/50 — it's just probability.
Practise this with real GAMSAT-style questions
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