# DBT JRF 2022 — Question 140

Exam: DBT JRF 2022 · Section: B · Topic: Animal Biotechnology › Animal Cloning - Cell Cycle Synchronization · Difficulty: Medium

## Question

In animal cloning, donor somatic cells should be in which stage of cell cycle?

## Options

- **A.** G1
- **B.** S
- **C.** G2
- **D.** G0

## Answer

Option C

## Explanation

Donor cell stage for SCNT: G0 (quiescent): In somatic cell nuclear transfer (SCNT/animal cloning), the donor somatic cell's cell cycle stage is CRITICAL: • Optimal stage: G0 (quiescent, serum-starved state) or early G1. • Why G0? - G0 nucleus is in a quiescent state with decondensed chromatin. - Compatible with the oocyte's MPF (M-phase Promoting Factor / CDK1-Cyclin B) environment. - MPF causes nuclear envelope breakdown and chromatin condensation. - G0/G1 cells respond optimally to oocyte reprogramming factors. - Chromosomes are fully replicated only once (avoid re-replication problems). • How to achieve G0: Serum starvation for 2–5 days → cells exit cycle and enter quiescence. Landmark: Dolly the sheep (1996) was cloned from a G0-synchronised mammary gland epithelial cell. Note: G2 cells have already duplicated their DNA; S-phase cells are in replication — both are problematic for nuclear transfer. Answer: Donor somatic cells should be in G0 (quiescent) stage before nuclear transfer for optimal reprogramming.

Source: https://mypyqbuddy.com/questions/in-animal-cloning-donor-somatic-cells-should-be-6a104cd5920734408bc0c79b