Although almost all of the genetic material of "Dolly" comes from the nucleus of the mammary cells of white-faced ewes, in addition to the genetic material existing in the nucleus in the form of chromosomes, there is also a small amount of genetic material existing in the form of circular DNA in the mitochondria outside the nucleus. When the nucleus of the egg cells of black-faced ewes is removed, the mitochondria are not removed, but remain in the cytoplasm of the egg cells. Therefore, the genetic material of Dolly not only comes from breast cells, but also comes from mitochondria in egg cells.
However, compared to the genetic material in the nucleus, the genetic material in mitochondria is insignificant in quantity and only serves the function of mitochondria, with little impact on Dolly's physical development and overall characteristics. Therefore,"Dolly" is basically the same as a white-faced ewes of the same age.