65. In animal cloning, donor somatic cells should be in which stage of cell cycle?
A. G1,
B. S,
C. G2,
D. G0

Introduction:

Animal cloning, specifically somatic cell nuclear transfer (SCNT), involves transferring the nucleus of a donor somatic cell into an enucleated egg cell. The success of this cloning technique depends not only on the quality of the cells used but also on the stage of the cell cycle the donor somatic cells are in. The donor somatic cell must be in a particular stage of the cell cycle for successful reprogramming and development into a viable organism.

Cell Cycle Stages:

The cell cycle consists of four main phases:

• G1 (Gap 1): The cell grows and synthesizes proteins necessary for DNA replication.

• S (Synthesis): The cell replicates its DNA.

• G2 (Gap 2): The cell prepares for mitosis by producing proteins required for division.

• M (Mitosis): The cell undergoes division to form two daughter cells.

• G0 (Resting Phase): Some cells exit the cell cycle and remain in a non-dividing, quiescent state.

The Role of the G1 Phase in Cloning:

For successful cloning, the donor somatic cell should be in the G1 phase of the cell cycle. Here’s why:

• G1 Phase (Best for Cloning): During G1, the cell has not yet replicated its DNA, which is crucial for the reprogramming process. If the donor cell is in the S phase or G2, the DNA is already undergoing replication or repair, making it more difficult for the nucleus to be reprogrammed effectively by the egg cytoplasm. The G1 phase provides the optimal conditions for reprogramming and allows the reprogramming factors from the egg to reset the somatic cell nucleus to a state suitable for development.

Why Not Other Phases?

• S Phase: DNA is being replicated, which can interfere with the process of reprogramming, as the S phase DNA structure might not be compatible with the reprogramming factors from the egg.

• G2 Phase: Cells are preparing for mitosis, and the chromatin structure might be more condensed, making it harder for the egg cytoplasm to reprogram the nucleus.

• G0 Phase: Cells are in a resting phase and not actively preparing for division, which may hinder the process of reprogramming needed for cloning.

Correct Answer:

A. G1 – Donor somatic cells should ideally be in the G1 stage of the cell cycle during animal cloning for optimal reprogramming and successful development.

Conclusion:

The G1 phase of the cell cycle is the most favorable stage for donor somatic cells in animal cloning. At this stage, the cells are primed for reprogramming, making them more responsive to the reprogramming factors present in the egg cell cytoplasm. Understanding the importance of the cell cycle stages in cloning can help improve the efficiency and success rate of cloning technologies.