How It Works: Adult Cell Cloning (Somatic Cell Nuclear Transfer)

How It Works: Adult Cell Cloning (Somatic Cell Nuclear Transfer)

Adult cell cloning — the technique used to create Dolly the sheep in 1996 — works by replacing the nucleus of an egg cell with the nucleus from a differentiated body cell. This allows an egg to develop using the full genetic information from an adult organism. Here is the step-by-step mechanism:

1. Collect a body (somatic) cell from the donor organism — any non-reproductive cell works (e.g., a mammary gland cell was used for Dolly). This cell contains a diploid nucleus with the complete genome of the donor.
2. Collect an egg cell from a female of the same species and remove its nucleus (enucleate the egg). The enucleated egg now has no genetic material but retains the cytoplasm, which contains factors needed for early embryo development.
3. Insert the donor nucleus into the enucleated egg cell. The egg now contains the genome of the adult donor.
4. Stimulate the egg to divide — typically using an electric shock, which mimics the signal that triggers fertilisation. The egg begins mitotic division.
5. Allow the embryo to develop in culture to the early embryo stage.
6. Implant the early embryo into the uterus of a surrogate mother, who carries the pregnancy to term.
7. The offspring is born genetically identical to the original donor organism (not the surrogate or the egg donor).

The technique is inefficient — Dolly was the only successful clone from 277 attempts — and cloned animals often show accelerated ageing and health problems. This makes therapeutic rather than reproductive cloning the more scientifically promising application.