Somatic cellnuclear transfer.

Somatic cell nuclear transfer takes its name from its two components. A somatic cell is any ordinary body cell, other than an egg or sperm cell – typically a fibroblast grown from a banked skin biopsy. Nuclear transfer describes the core act of the technique: moving a nucleus, the structure inside a cell that holds its DNA, from that somatic cell into an egg whose own nucleus has been removed. The method was proven in mammals with the birth of Dolly the sheep in 1996, and has since been used across many species.¹

The recipient egg is collected from a female of the same species, and under a high-powered microscope, an embryologist uses a fine glass pipette to remove its nucleus without damaging the rest of the cell – a step called enucleation. Separately, a donor fibroblast from the banked line is prepared and placed against the enucleated egg. A carefully controlled electrical pulse fuses the two cells into one, and the same or a following pulse activates the egg, triggering it to behave as though fertilisation had occurred.

The reconstructed embryo is cultured for several days, monitored for normal division, before the embryos judged most likely to succeed are selected for transfer into a surrogate mother. Not every reconstructed embryo divides normally, and not every transferred embryo results in a pregnancy; this is why cloning programmes are described as ranges rather than certainties, and why several attempts are often planned for.

Once an embryo is transferred, the pregnancy proceeds and is monitored like any other of that species: by ultrasound at set intervals, with veterinary oversight of the surrogate throughout. Gestation length follows the species' own biology – roughly two months for cats, around two months for dogs, about thirteen months for camels, and roughly eleven months for horses – and cannot be shortened by the cloning process itself.

We report progress to owners at each stage, including when a pregnancy does not continue, which happens at a higher rate in cloned pregnancies than in natural ones. We do not present a due date as a promise, and we do not describe the resulting animal as anything other than what it is: a genetic twin of the donor, explained in full in cloning is a genetic twin.

The idea behind nuclear transfer is older than most people assume. Embryologists in the mid twentieth century moved nuclei between frog eggs to ask a simple question: does a cell that has already become skin or gut still carry every instruction needed to build a whole animal? The answer, confirmed over decades, was yes – though the older and more specialised the donor cell, the harder it was to make the instructions work again. That difficulty has never fully gone away, and it explains much of what follows.

The first mammal cloned from an adult cell was a sheep, born in Scotland in 1996 and reported the following year. She was one success out of several hundred reconstructed embryos. Cats followed in 2001, horses in 2003, dogs in 2005 and camels, in Dubai, in 2009. Each species brought its own obstacles: the timing of egg maturation, how the embryo is cultured, when and where it is transferred. Methods that work for one species rarely transfer unchanged to another, which is why a laboratory's experience with a particular species matters more than general claims about cloning.

Efficiency has improved since those first births, but it remains modest. Many reconstructed embryos stop dividing within days; some that are transferred do not implant; a proportion of pregnancies end early. None of this is hidden in the scientific literature, and none of it should be hidden from an owner. It is the reason a programme plans several transfers rather than one, and the reason we give timelines as ranges. It is also why we recommend banking a line early, when the cells are young and grow well, rather than asking the method to work from a weaker starting point later.

Nuclear transfer copies the nuclear genome. It does not copy the small amount of DNA held in the mitochondria, which comes from the egg, and it does not copy anything the donor learned or experienced. Coat pattern, size and temperament are shaped partly by development in the womb and by the life that follows. A genetic twin is its own individual, and is best welcomed as one. Prices and stages are set out in full on Continue; cats start from $65,000, dogs are $85,000, camels start from $100,000 and horses are priced by consultation, with preservation quoted separately.

Every step above depends on having donor cells that are alive, healthy and available on demand – exactly what a banked cell line provides. Attempting to clone from tissue collected after death is far harder and less reliable, because cells begin to lose viability quickly once circulation stops, which is why we describe the first 72 hours after an animal's death as decisive for that option. Banking cells while an animal is alive removes that urgency and gives a cloning programme, should one ever be pursued, the best possible starting material.