# DBT JRF 2020 — Question 15

Exam: DBT JRF 2020 · Section: A · Topic: Cell Biology · Difficulty: Medium

## Question

Primary cilia biogenesis typically starts at the

## Options

- **A.** S and G2 phase of the cell cycle
- **B.** G1/G0 phase of the cell cycle
- **C.** G2 phase of the cell cycle
- **D.** S phase of the cell cycle

## Answer

Option B

## Explanation

Primary cilia are microtubule-based sensory organelles that assemble from the basal body (a modified centriole) and project from the cell surface. Their biogenesis is tightly linked to the cell cycle. During S phase and G2/M, centrioles are engaged in centrosome duplication and mitotic spindle formation — they cannot simultaneously form a basal body. Ciliogenesis therefore occurs in G1 or G0 (quiescent) phase, after cells exit mitosis. The primary cilium is resorbed at the G1/S transition before cell division resumes, coordinated by Aurora A kinase and HEF1 signalling.

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