A new way of reproducing

What is cloning?

It’s a new form of reproduction in which scientists make a genetic copy of a single creature. Cloning has long existed in nature, in lower life forms such as bacteria and yeasts, which reproduce by simply splitting into two creatures with the same genes. (Biologists call this fission.) Up to now, higher life forms have reproduced sexually, uniting a sperm and an egg that each carry a set of chromosomes, creating a new, unique individual with some genes from both parents. In human reproduction, for example, each baby gets half of its genetic endowment of 46 chromosomes from the mother, and half from the father. A human clone’s 46 chromosomes would all come from a single parent—making it, more or less, a carbon copy.

How does cloning work?

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The most common method is called nuclear transfer. It begins by sucking out the nucleus of an unfertilized egg, to create a blank genetic canvas. The egg, now called an ovacyte, then has a new set of genes installed, by being injected with the nucleus of a cell taken from the animal being cloned. The implanted ovacyte is given a small jolt of electricity, which “jump-starts” the egg’s usual process of cell division. Like any other fertilized egg, the ovacyte then begins to grow into an embryo, according to the genetic instructions in the implanted DNA.

What’s the point of doing this?

There are several motivations. In cloning animals, scientists hope to make copies of prize dairy cows and other animals that are difficult to breed, as well as to make new copies of creatures on the verge of extinction. The stakes for human cloning are much higher. In stem-cell or “therapeutic” cloning, scientists hope to use the technique to find cures for a host of diseases, including Alzheimer’s, Parkinson’s, and diabetes, as well as spinal-cord injuries. Scientists involved in this research inject a full set of chromosomes into a human egg and grow it into a proto-embryo, or blastocyst, of about 100 cells. The blastocyst is then killed and its cells harvested for research. The primitive cells, called stem cells, are capable of growing into skin, nerve, muscle, or any of the hundreds of different types of cells in the human body. Researchers hope to figure out how to coax the stem cells into growing into new, healthy tissue and implant them into people with genetic diseases. Theoretically, stem cells could even be coaxed to morph into entire new livers, kidneys, pancreases, hearts, or other organs.

What about making babies?

Though still on the fringes, the demand is there for reproductive cloning too. In vitro fertilization clinics now produce about 170,000 babies a year in the U.S. alone, but such clinics still have a significant failure rate, especially when the would-be mother is in her mid-30s or older. Renegade reproductive scientist Panos Zavos, who is openly pursuing human cloning, says he already has a waiting list of 5,000 couples. In reproductive cloning, the blastocyst would grow in the lab for about a week, and then be implanted in a female’s uterus, where it would grow to term.

Would a clone be an exact replica?

No. The basic genetic blueprint would be the same, but how it’s executed would be affected by everything from conditions in the mother’s womb to experiences in the world. Decades of research suggest that our identities are 50 percent determined by our genes, and 50 percent by our environment. “To produce another Wolfgang Amadeus Mozart,” says Harvard University geneticist Leon Eisenberg, “we would need not only Wolfgang’s genome but his mother’s uterus, his father’s music lessons, his parents’ friends and his own, the state of music in 18th-century Austria, Haydn’s patronage, and on and on, in ever-widening circles.”

Can we clone animals?

Yes. The big breakthrough came in 1996, with the birth of Dolly, the famous cloned sheep. Scottish biologist Ian Wilmut and his colleague Keith Campbell overcame obstacles that had thwarted other scientists. Dolly was born after 277 failed attempts by the two scientists to produce a sheep that was carried to term.

How far have we come since Dolly?

Not very far. Cloning is still a hit-or-miss affair, dominated by misses. Although scientists have cloned adult sheep, mice, cattle, goats, and pigs, about 97 percent of these attempts have failed. The vast majority of the animals have died in the womb or shortly after birth. In other cases, they’ve suffered from arthritis, immune-system deficiencies, or a form of gigantism called “large offspring syndrome.” There are plenty of species—rabbits, rats, cats, dogs, and monkeys among them—that have so far proved uncloneable.

What’s going wrong?

The process of reproduction, it turns out, is far more complicated than simply Xeroxing one creature’s genes. Scientists now suspect that chromosomes contain certain chemical “tags” that are like light switches that go on and off. Once implanted in an egg, the chromosomes must be activated at exactly the right time and in the right sequence—or the encoded message of the DNA can’t be properly read. The result is a flawed copy. In current cloning techniques, any clone that survives to term is a lucky shot in the dark—and even then, it contains subtle flaws that show up later. In other words, modern scientists may have a crude recipe to make life, but they lack evolution’s—or God’s—exquisite timing and technique.

How close are we to cloning people?

We’re at least five or 10 years away. With our present technology, experts say, most pregnancies would result in miscarriages or terrible birth defects. “Cloning is way too dangerous to do now,” says Dr. Gregory Stock, a developmental biologist at the University of California. But that doesn’t mean it’ll be five years or 10 before the first cloned baby is born. “Before responsible medical professionals believe that it is safe enough to do,” Stock says, “it will be done by somebody else.”

The fight to ban cloning