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← Theoretical 1

Q40 — Elephants, LIF6, and Cancer Resistance

Theoretical 1 Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Molecular Evolution & Neutral Theory Cell Junctions, Extracellular Matrix & Cell Death

Elephants live about as long as humans, but cancer occurs in 17% of humans and only about 5% of elephants. Researchers found that a “zombie gene” (Leukemia Inhibitory Factor 6, LIF6) helps prevent cancer in elephants. In both humans and elephants, p53 suppresses cancer cell growth and promotes apoptosis. The LIF gene family was thought to have lost protein-coding ability, but LIF6 was somehow revived in elephants, damaging the mitochondrial membrane in mutated cells and causing rapid destruction of genetically defective cells. These changes are estimated to have occurred 25–30 million years ago, as elephant ancestors began growing larger.

Using the information, determine whether the following statements are true or false:

A. The increase in the size of the elephants promoted their survival.
B. An increase in body size is usually accompanied by a higher probability of developing cancer.
C. The new function of the LIF6 gene is a key determinant of elephant body size and species survival.
D. Probability of cancer development increases as the animal ages.
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Question reproduced from IBO 2022, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)