medium · SAT Reading & Writing

Octopuses and squid can recolor their skin faster than almost any other animal, but a subtler trick has drawn recent attention. These cephalopods routinely "edit" their own RNA—the molecular messages that carry instructions from genes to cells—recoding those messages on the fly rather than altering the underlying DNA. In cold water, for instance, some squid rewrite the RNA governing nerve-signal proteins, tuning their nervous systems to the temperature. Because such edits leave the genome untouched, they let the animal adjust to its surroundings within its own lifetime instead of waiting for the slow work of inherited mutation. Which choice best states the main idea of the text?

1. By rapidly recoloring their skin, octopuses and squid can camouflage themselves faster than nearly any other animal.
2. Cephalopods can adjust to conditions such as cold water by editing their RNA, adapting within a single lifetime rather than relying on inherited mutations.
3. RNA editing has replaced inherited mutation as the primary way cephalopods evolve as a species.
4. Some squid rewrite the RNA that governs their nerve-signal proteins when the surrounding water turns cold.

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