Explain why cloning of Dolly, the sheep was such a major scientific breakthrough ?

Explanation

(i) Transgenes is the proces of introdcution of extra DNA into the genome of the animals of create and maintain stable heritable characters. Such animals are called transgenic animals.
(ii) .Dolly. the transgenic clone was developed by the nuclear transfer technique.
(iii) This was a major breakthrough since it showed that genetic manipulations are possible in adult cells. Such transgenic animals serve as good models for understanding human diseases which help in investigation of new treatments for disease . Eg : Transgenic models exists for many human disease such as cancer, rheumatoid arthritis etc.
(iv) Further Dolly was the first animal to be cloned from a differentiated somatic cell taken from an adult animal without the process of fertilization.