BT EXPLAINER: 30 years after Dolly, here's why cloning is still making headlines

Thirty years after Dolly the sheep was born, cloning has become a specialised biotechnology tool rather than a simple way to copy animals. It is used in research, agriculture and conservation, but it remains costly, inefficient and ethically contested.

How is animal cloning carried out?

Most animal cloning uses somatic cell nuclear transfer. Scientists remove the nucleus from a body cell of the donor animal and place it into an egg cell whose own nucleus has been removed. In Dolly’s case, the donor cell came from a mammary gland. An electric pulse helps fuse the cells. If the egg develops into an embryo, it is implanted into a surrogate uterus. The animal born is nearly identical in DNA to the donor.

How efficient is animal cloning?

Cloning mammals remains highly inefficient. Many reconstructed embryos do not develop normally, and multiple surrogate pregnancies may be needed for one live birth. Dolly was produced after 277 attempts. The process also needs specialised equipment, donor cells, egg cells and surrogates, which makes it expensive and difficult to scale.

What are the challenges associated with animal cloning?

The main difficulty is not copying DNA but resetting the donor cell so it behaves like a newly fertilised embryo. This epigenetic reprogramming is often incomplete, which is why many clones fail to develop properly. Clones also do not reproduce memories, behaviour or life experience. Welfare concerns remain because low success rates can involve suffering for embryos and surrogates. Human cloning is widely prohibited or heavily restricted because of safety and ethical risks.

Where is animal cloning used?

Cloning is used to reproduce livestock with valuable traits such as high productivity, strong genetics or disease resistance. Australia allows horse cloning, and cloned horses have appeared in equestrian sport. China and the United States offer commercial pet cloning for cats and dogs. Cloning research also led to induced pluripotent stem cells, which are used to study disease, test drugs and explore regenerative medicine.

In conservation, scientists cloned Elizabeth Ann, a black-footed ferret, in 2020 using preserved genetic material to boost diversity in an endangered species. By contrast, true cloning cannot bring back long-extinct animals such as the woolly mammoth because intact DNA, a suitable egg and a close surrogate are unavailable. Researchers are instead exploring gene-editing tools such as CRISPR to create animals with selected extinct traits.

Famous instances of cloning

Dolly, created by Ian Wilmut’s team at the Roslin Institute, remains the best-known example. Singer Barbra Streisand had her dog Samantha cloned into two puppies, though they developed different personalities. In 2024, researchers in China reported a cloned rhesus monkey, saying the work could aid drug testing, though animal welfare advocates questioned whether the suffering involved was justified.