I’m not a huge fan of sci-fi, but one sci-fi movie I have seen is “Jurassic Park.” You’ll remember that the dinosaurs in that park were cloned from dinosaur blood (which contains DNA because reptiles, unlike mammals, have red blood cells with nuclei), and that blood was from the stomachs of mosquitoes that had bitten dinosaurs and then gotten preserved in amber. Well, that reconstruction feat is impossible for scientists at our present stage of knowledge and technical abiliity—for the very same reasons it’s impossible to re-create any ancient organism from “fossil DNA.” This is relevant because of recent speculations, fueled by Harvard geneticist George Church and picked up and disseminated widely by the press, that we might be able to clone a human Neanderthal, since we now have a sequence of the Neanderthal genome. (I’ve written before about George Church’s accommodationism; see here and here.)
First a bit about how animals are cloned. It’s usually done by taking a nucleus out of one cell (the nucleus contains most but not all of an organism’s DNA) and then transferring it to the egg of another individual from which the nucleus has been removed. For example, you could clone your cat before it dies by removing a bit of tissue, taking out the nucleus from one cell, and putting that nucleus into the egg of a female cat from which the nucleus has been removed. The egg would then be implanted into a “surrogate cat,” which would carry the “fertilized” egg having the genetic constitution of your own cat. If all goes well—and it often doesn’t!— the cat will produce a kitten largely genetically identical to your cat, enabling you, in principle, to have the same pet forever. (This isn’t guaranteed, though, as the mitochondrial DNA of your pet would not be transferred in this procedure, and somatic cells in the body undergo mutations during the life of an organism, so the skin cell of your cat won’t be genetically identical to the fertilized egg that produced it. See my discussion of this at the end of the piece.)
At any rate, this whole kerfuffle arose when Church floated the issue of producing a modern, living Neanderthal in this way. As Huffpo reports:
In a controversial interview that has ignited commentary across the world, a respected Harvard professor of genetics has suggested an “extremely adventurous female human” might someday serve as surrogate mother for a cloned Neanderthal baby.
Besides saying that the cloning of a live Neanderthal baby would be possible in our lifetime, George Church told Der Spiegel magazine that using stem cells to create a Neanderthal could have significant benefits to society. “The first thing you have to do is to sequence the Neanderthal genome, and that has actually been done,” Church said.
“The next step would be to chop this genome up into, say, 10,000 chunks and then … assemble all the chunks in a human stem cell, which would enable you to finally create a Neanderthal clone,” Church told Der Spiegel.
Scientists completed the first sequence of the Neanderthal genome in 2010, finding genetic evidence suggesting ancestors of modern humans successfully interbred with Neanderthals, at least occasionally. More recent research has suggested Neanderthal DNA makes up 1 percent to 4 percent of the genomes of modern Eurasians. [The 10 Biggest Mysteries of the First Humans]
The benefits, according to Church, include an increase in genetic diversity. “The one thing that is bad for society is low diversity,” Church said. “If you become a monoculture, you are at great risk of perishing. Therefore the recreation of Neanderthals would be mainly a question of societal risk avoidance.”
In his book “Regenesis: How Synthetic Biology Will Reinvent Nature and Ourselves” (Basic Books, 2012), Church writes, “If society becomes comfortable with cloning and sees value in true human diversity, then the whole Neanderthal creature itself could be cloned by a surrogate mother chimp — or by an extremely adventurous female human.”
The HuffPo piece reports that Church’s statements have been overblown by the press, and he’s clarified his stand (see video at the link), saying that he wasn’t actually looking for a woman to bear a Neanderthal baby:
Church’s statements in the Der Spiegel interview have been wildly distorted, according to some observers. “There’s always a danger in taking one little comment and blowing it out of proportion,” John Hawks, associate professor of biological anthropology at the University of Wisconsin–Madison, told LiveScience.
“He’s really talking about science fiction,” Hawks said of Church’s comments, adding that with current technology, the cloning of any long-extinct species is “completely impossible.”
“We are a long way from taking DNA information and making a living cell from it,” Hawks said. And while the cloning and rebirth of extinct animals and humans sounds fascinating, it’s really not a scientific priority. “It seems to capture people’s imagination, but it’s not on anyone’s agenda,” Hawks said.
. . . Church himself has distanced himself from the media frenzy surrounding his Neanderthal commentary. “The real story here is how these stories have percolated and changed in different ways,” Church told the Boston Herald. “I’m sure we’ll get it sorted out eventually.”
Yet I still see claims all the time that we can use “fossil DNA” to re-create dinosaurs, mammoths, or other extinct life forms—so long as we have their DNA. But, as Hawks noted above, this is impossible with modern technology. And while there are several reasons why it’s impossible, there’s one big problem that will take decades to overcome:
Genes occur on chromosomes.
Human DNA, for example is arrayed on 23 pairs of chromosomes, and those chromosomes are unique bodies, each carrying their own subset of genes arrayed in a particular linear order. Chromosomes are complicated structures (read about them here), for they contain not just DNA, but specific DNA-associated proteins (“histones”), a “centromere,” a special part of the chromosome which helps it move to a daughter cell when cells divide, and “telomeres,” repeated bits of DNA at the end of chromosomes that protect the chromosome from degrading.
To produce an organism, its genome must be sitting on chromosomes, and on the proper number of chromosomes. You can’t just take a whole genome and stick it into a recipient cell, expecting that cell to behave normally. The genome first has to be assembled in proper order—and that means the perfectly proper order (no room for error here), with all the bits in the right sequence. Then it has to be packaged into those chromosomes, for without chromosomes cells can’t divide properly and you can’t produce a whole organism from that single cloned cell. To get an organism from one cell, there has to be millions of cell divisions.
Not only do we lack the ability to assemble bits of DNA (what we have from Neanderthals) into a complete genome, but we are nowhere close to putting that DNA onto chromosomes in the proper order. Until we do that, we won’t be able to bring back any species from fossil DNA. I doubt that we’ll have this ability within the next 50 years, if that.
But the problems go beyond that. DNA degrades with age, and some types of degradation (like changes of one DNA “base” to another) cannot be detected by sequencing, but would still render the reconstructed clone inviable because those mutations would be lethal in the re-created organism. The genomes of many species, including ours, contain repeated elements dispersed throughout the genome. Much of this is “junk,” some of it may have unknown but essential functions, but all of it would cause problems trying to reconstruct an ancestral DNA sequence. We don’t know exactly how many of these things there are nor exactly where they all sit on the DNA. If you screw that up, you will likely not get a viable “egg.” Finally, trying to assemble bits of fossil DNA (or DNA “cloned” from those fossil sequences) is likely to cause copying errors, creating even more mutations that will make the “clone” inviable.
And, of course, for the Neanderthals we don’t have a complete DNA sequence in order, and there is controversy about how much is original, how much may be contaminated, and so on.
Now I am not a molecular biologist, and am just speculating about what I know as an evolutionary geneticist. There may eventually be ways to assemble a complete fossil genome with all the bits in the proper places, and even to ensure that the repeated DNA elements are in the right places and that the assembly process doesn’t itself create errors.
But there is no way I know around the problem of having to put that DNA onto the proper number of chromosomes in the proper order. We can’t just assemble chromosomes the way we can synthesize DNA. And until we can do that, reconstructing dinosaurs, Neanderthals, or any species from fossil DNA is simply out of the question.
So, as Hawks noted above, take this idea as science fiction, as it was in “Jurassic Park.” And the next time somebody tells you that cloning Neanderthals or dinosaurs is within the realm of science, remember the chromosomes.
But, of course, you can still clone your pet, because it’s alive and has its genome properly packaged onto chromosomes. Remember, though, that the clone won’t be genetically identical to Fluffy because of those factors I mentioned above. An article by Dr. Sophia Yin tells you the difference between a cat and her cloned offspring.
The picture below shows you what to expect when you clone your cat: Rainbow, on the left, is the genetic mother, via cloning, of cat CC (“copy cat”) on the right. They don’t even look alike: Rainbow is a calico and CC a tiger tabby with patches. Why are they different? Coat color genes are inactivated in body cells, and which body cell you use as the donor nucleus can affect the color of its offspring. As Dr. Yin explains, cloning a tuxedo cat may produce another tuxedo cat, but with the white and black patches in different places. And don’t expect your cloned cat to behave the same way, either. The same processes that make a clone look different from its donor can make the clone behave differently from its donor.
As Yin notes:
Consequently, your chances of ever having your pet cloned are slim. But even if the technology were available, the take home message with CC is that cloning will not resurrect your pet. Instead, you would be more likely to get something that looked similar to your beloved pet but that acted quite differently, or your clone could even end up looking like a complete stranger. Now that would be a dream, turned nightmare!
The result of cat cloning: donor (left) and clone (right)
