Explanation:

Dolly the sheep was the first mammal to be cloned from an adult somatic cell using a process called somatic cell nuclear transfer (SCNT). In this process, the nucleus of an adult somatic cell (in this case, an udder cell) is transferred into an enucleated egg cell (from which the nucleus has been removed). The resulting reconstructed egg is then stimulated to divide and develop into an embryo, which is eventually implanted into a surrogate mother for gestation.

Genetic Similarity:

The genetic similarity of Dolly the sheep can be understood by considering the source of the genetic material used in the cloning process.

- The mother from which the nucleated fertilized egg was taken: This option refers to the mother from which the egg cell was obtained. However, in the process of somatic cell nuclear transfer, the original egg cell is enucleated (its nucleus is removed) and a new nucleus from an udder cell is inserted. Therefore, the genetic material of the egg cell does not contribute to Dolly's genetic similarity.

- The mother from which the nucleus of the udder cell was taken: This option refers to the genetic source of the nucleus that was inserted into the enucleated egg cell. In the case of Dolly, the nucleus used in the cloning process was taken from an udder cell of a female sheep. This means that Dolly's genetic similarity is primarily derived from the nucleus of the udder cell donor.

- The surrogate mother: The surrogate mother plays a role in gestating and giving birth to the cloned embryo but does not contribute genetically to the cloned offspring. The surrogate mother's genetic material is not involved in the cloning process and therefore does not contribute to Dolly's genetic similarity.

- Both the surrogate mother and the nuclear donor mother: This option suggests that both the surrogate mother and the nuclear donor mother contribute to Dolly's genetic similarity. However, as explained above, the surrogate mother's genetic material is not involved in the cloning process, and therefore, Dolly's genetic similarity is primarily determined by the nucleus of the udder cell donor.

Conclusion:

Based on the process of somatic cell nuclear transfer and the role of genetic material from different sources in the cloning process, the correct answer is option B: The mother from which the nucleus of the udder cell was taken. This is because Dolly's genetic similarity is primarily derived from the nucleus of the udder cell donor, rather than the egg cell or the surrogate mother.