In the described cloning process in sheep, what is the step immediately after inserting copies of the DNA into the nuclei of sheep body cells?

• A. Embryo implanted into uterus
• B. Nucleus is transplanted into enucleated egg cell
• C. Jellyfish gene inserted into DNA
• D. Embryo grown in culture

Answer: (B)

The step being tested is the nucleus transfer in somatic cell nuclear transfer cloning. After a donor body cell’s DNA is prepared, the immediate next move is to transplant that nucleus into an egg cell from which the original nucleus has been removed (enucleated). This places the donor genome into an egg that can reactivate and begin embryonic development. Once the nucleus is inside, the egg is stimulated to activate, starts to divide, and the embryo can be cultured to an appropriate stage before being implanted into a uterus. The other options describe steps that occur later (implantation or culture) or are unrelated to the cloning process (such as inserting a jellyfish gene).