Cloning an animal is primarily achieved through a process that creates a genetic copy, most commonly using a technique called Somatic Cell Nucleus Transfer (SCNT).
Cloning is a form of reproduction that produces a genetically identical individual. The most widely used and successful technique for cloning animals is Somatic Cell Nucleus Transfer (SCNT). This method involves taking genetic material from one animal and transferring it into an egg cell from which the original nucleus has been removed.
Understanding Somatic Cell Nucleus Transfer (SCNT)
SCNT creates a clone by replacing the nucleus of an unfertilised ovum (egg cell) with the nucleus of a body (somatic) cell from the animal to be cloned. This modified egg cell is then stimulated to develop into an embryo.
Here’s a breakdown of the typical SCNT process:
- Obtain the Somatic Cell: A somatic cell (any body cell other than a sperm or egg cell), containing the complete set of DNA from the animal to be cloned, is collected. Examples include skin cells, muscle cells, or mammary gland cells.
- Obtain the Egg Cell (Ovum): An unfertilised egg cell is collected from a donor animal (often of the same species).
- Remove the Egg's Nucleus: The nucleus, which contains the original genetic material of the egg cell, is carefully removed. This leaves behind an egg cell with no nucleus, essentially a 'blank slate'.
- Transfer the Somatic Cell Nucleus: The nucleus from the somatic cell (containing the DNA of the animal to be cloned) is then transferred into the enucleated egg cell. This can be done by injecting the nucleus directly or by fusing the somatic cell with the egg cell using an electric pulse.
- Stimulate Development: The reconstructed egg cell, now containing the donor animal's nucleus, is stimulated (usually with an electric shock or chemicals) to begin dividing, mimicking the process of fertilization.
- Culture the Embryo: The resulting embryo is cultured in a laboratory for a few days until it reaches a certain stage of development (e.g., blastocyst stage).
- Transfer to Surrogate Mother: The developing embryo is then implanted into the uterus of a surrogate mother animal.
- Gestation and Birth: If the pregnancy is successful, the surrogate mother carries the embryo to term, and a clone genetically identical to the somatic cell donor is born.
Key Components in SCNT
The SCNT process relies on successfully handling and combining specific cellular components:
| Component | Source | Purpose |
|---|---|---|
| Somatic Cell Nucleus | Animal to be cloned | Provides the genetic blueprint for the clone |
| Enucleated Ovum | Donor animal | Provides the cellular machinery for development |
| Surrogate Mother | Recipient animal | Provides the environment for embryonic growth |
This technique has been used to clone various animals, including sheep (like Dolly), cows, pigs, dogs, and cats, demonstrating that replacing the original nucleus of an unfertilised ovum with the nucleus of a body cell can indeed lead to the formation and development of an embryo that is a genetic copy of the donor animal.
