Ever since University of North Carolina paleontologist Mary Schweitzer discovered their soft tissue in dinosaur fossils, the question has been posed to modern science of ancient creatures: Can we ever find authentic dinosaur DNA? And if so, will we not be able to recreate these amazing animals with its help?
It is not easy to give definite answers to these questions, but Dr. Schweitzer nevertheless agreed to help us understand what we know today about the genetic material of dinosaurs and what we can count on in the future.
Can we get DNA from fossils?
This question should be understood as "can we get dinosaur DNA"? Bones are composed of the mineral hydroxyapatite, which has such a high affinity for DNA and many proteins that it is actively used in laboratories today to purify their molecules. The bones of dinosaurs have lain in the ground for 65 million years, and the probability is quite high that if you start actively looking for DNA molecules in them, then it is quite possible to find. Simply because some biomolecules can stick to this mineral like Velcro. The problem, however, will not be so much simply finding DNA in dinosaur bones as proving that these molecules belong to dinosaurs and did not come from any other possible source.
Will we ever be able to recover genuine DNA from a dinosaur bone? The scientific answer is yes. Anything is possible until proven otherwise. Are we now able to prove the impossibility of extracting dinosaur DNA? No, they cannot. Do we already have a genuine dinosaur gene molecule? No, this question is still open.
How long can DNA be preserved in the geological record and how can one prove that it belongs to a dinosaur, and did not get into a sample already in the laboratory along with some contaminant?
Many scientists believe that DNA has a fairly short shelf life. In their opinion, these molecules are unlikely to last longer than a million years, and certainly not more than five to six million years at best. This position deprives us of any hope of seeing the DNA of creatures that lived over 65 million years ago. But where did these numbers come from?
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Scientists working on this problem put DNA molecules in hot acid and timed the time it took for them to decay. High temperature and acidity have been used as substitutes for long periods of time. According to the findings of the researchers, DNA decays rather quickly. The results of one such study, which compared the number of DNA molecules successfully extracted from samples of different ages - from several hundred to 8000 years - showed that the number of extracted molecules decreases with age. Scientists have even been able to simulate the "decay rate" and predicted, although they did not verify this claim, that it is extremely unlikely to find DNA in Cretaceous bones. Ironically, this same study showed that age alone cannot explain the breakdown or preservation of DNA.
On the other hand, we have four independent lines of evidence that molecules chemically similar to DNA can localize in the cells of our own bones, and this is in good agreement with expecting such finds in dinosaur bones. So, if we extract DNA from bones belonging to dinosaurs, how can we be sure that this is not the result of later contamination?
The idea that DNA can last for so long does have a pretty slim chance of success, so any claim to find or recover real dinosaur DNA must meet the most stringent criteria. We offer the following:
1. The DNA sequence isolated from the bone should match what would be expected based on other data. Today, there are over 300 signs that link dinosaurs to birds, and convincingly proves that birds evolved from theropod dinosaurs. Therefore, the DNA sequences of dinosaurs obtained from their bones should be more similar to the genetic material of birds than to the DNA of crocodiles, while differing from both. They will also be different from any DNA coming from modern sources.
2. If the dinosaur DNA is real, it will obviously be highly fragmented and difficult to analyze with our current methods, designed to sequence healthy and happy modern DNA. If Tirex DNA turns out to be made up of long strings that are relatively easy to decipher, then most likely we are dealing with contamination, and not genuine dinosaur DNA.
3. The DNA molecule is considered more fragile compared to other chemical compounds. Therefore, if authentic DNA is present in the material, then there must be other, more durable molecules, for example, collagen. At the same time, the connection with birds and crocodiles should also be traced in the molecules of these more stable compounds. In addition, in the fossil material, for example, lipids that make up cell membranes can be found. Lipids are more stable than proteins or DNA molecules on average.
4. If proteins and DNA have been successfully preserved from the Mesozoic times, their connection with dinosaurs should be confirmed not only by sequencing, but also by other methods of scientific research. For example, binding proteins to specific antibodies will prove that these are indeed soft tissue proteins and not contamination from external rocks. In our studies, we were able to successfully localize a chemically DNA-like substance inside T. Rex bone cells using both DNA-specific techniques and antibodies to proteins associated with vertebrate DNA.
5. Finally, and perhaps most importantly, proper supervision should be applied at all stages of any research. Along with the samples from which we hope to extract DNA, it is necessary to investigate the host rocks, as well as all chemical compounds used in the laboratory. If they also contain sequences of interest to us, then most likely they are just pollutants.
So will we ever be able to clone a dinosaur?
In a sense. Cloning, as is commonly done in the laboratory, is the insertion of a known piece of DNA into bacterial plasmids. This fragment replicates whenever a cell divides, resulting in many copies of identical DNA. Another method of cloning involves placing a whole set of DNA into viable cells, from which their own nuclear material has been removed in advance. Then such a cell is placed in the host's organism, and the donor DNA begins to control the formation and development of offspring, completely identical to the donor. The famous Dolly the sheep is an example of the use of just this method of cloning. When people talk about "cloning a dinosaur," they usually mean something like this. However, this process is incredibly complex, and, despite the unscientific nature of this assumption,the likelihood that we will someday be able to overcome all the inconsistencies between DNA fragments from dinosaur bones and produce viable offspring is so small that I class it as "not possible."
But just because the likelihood of creating a real Jurassic Park is scanty, it cannot be said that it is impossible to restore the original dinosaur DNA itself or other molecules from ancient remains. In fact, these ancient molecules could tell us a lot. After all, all evolutionary changes must first occur in genes and be reflected in DNA molecules. We can also learn a lot about the longevity of molecules in vivo directly, rather than through laboratory experiments. Finally, recovering molecules from fossil specimens, including dinosaurs, provides us with important information about the origin and distribution of various evolutionary innovations, such as feathers.
We still have a lot to learn in molecular analysis of fossils, and we must proceed with the utmost care, never overestimating the data we receive. But we can extract so many interesting things from the molecules preserved in the fossils that it certainly deserves our efforts.