In somatic cell nuclear transfer, the donor nucleus is introduced by:

• A. Replacing the egg's nucleus with a donor nucleus from an adult cell.
• B. Extracting the nucleus from an egg and inserting it into the donor cell.
• C. Activating the egg with chemicals or electricity without any nucleus.
• D. Transferring the embryo into a uterus.

Answer: (B)

In somatic cell nuclear transfer, the nucleus from a donor somatic cell is introduced by replacing the egg’s own nucleus with that donor nucleus. The egg is first enucleated, removing its nucleus, and then the donor nucleus is inserted into the enucleated egg. This reconstituted egg is then activated to begin embryonic development. The idea is to have the donor nucleus take over inside the egg, not to move the egg’s nucleus into the donor cell, and not to activate an egg that lacks any nucleus or to implant an embryo directly into a uterus.