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← Theoretical 2

Q97 — Telomerase-Dependent vs Alternative Telomere Lengthening in Testis

Theoretical 2 Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
DNA Structure & Replication

There are two mechanisms of telomere lengthening in a cell: the telomerase-dependent (TEL) pathway and the alternative telomere-lengthening (ALT) pathway. The activity of the TEL and ALT pathways has been studied in a number of healthy human tissues based on the expression of the genes involved in those pathways (see Figure). A pathway is considered active if the relative activity value is greater than 0.

Gene effect is measured by the Partial Influence (PI) metric. If PI is greater than 0, the gene activates the pathway; if less than 0, it suppresses the pathway; if 0, it does not affect the pathway activity. The greater the absolute value of PI, the greater the effect of that gene on pathway activation. Relative expression is the natural logarithm of the expression of a gene in a sample divided by the mean of the expression of that gene in all samples.

Three-panel figure. Panel C: violin/box plots of TEL relative activity across six age groups (20-29 through 70-79), with the 20-29 group standing out as significantly elevated relative to the rest. Panel D: violin/box plots of ALT relative activity across the same six age groups, showing broadly overlapping, similarly wide distributions with no clear age trend. Panel E: a TMM scatter plot of ALT vs. TEL relative activity, colored by age group, showing two loose clusters. Figure (panels C–E). The relative activity values of the TEL and ALT pathways in testis across age groups (C–D), and a TMM scatter plot for testis (E).

Two-panel figure. Panel F: gene influence (Partial Influence, PI) on TEL activity in testis, with TERC showing a large negative PI (strong inhibitor) and other genes showing smaller effects. Panel G: gene influence on ALT activity in testis, with RAD51 showing the largest positive PI (strongest activator) among the plotted genes. Figure (panels F–G). Gene influence on TEL and ALT pathway activity in testis, measured by Partial Influence (PI).

Using this information and analysis, determine whether the following statements are true or false.

A. RAD51 is the most critical factor resulting in activation of the ALT in testis.
B. TERC decreases the activation of the TEL pathway in testis
C. The relative activity values of the TEL pathway are clearly divided into two age groups
D. TEL pathway activity predominates at a younger age, while the ALT pathway is more important in older age
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Question reproduced from IBO 2022, Theoretical Paper 2, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)