Don't wait for dinosaurs :(
Why haven't dinosaurs been cloned yet?
Sergey Kiselyov, Post-science
Caution: Your inner teenager will find out the answer to this question and get a little upset.
After the movie "Jurassic Park", many people wondered: why can't we clone dinosaurs? Geneticist Sergey Kiselyov explained which three difficulties we will not see live tyrannosaurs and pterodactyls in the coming years.
– In those ancient times, the most common mosquitoes existed on Earth. As befits mosquitoes, they fed on the blood of animals, including dinosaurs. It happened that after drinking blood, he [the mosquito] sat on a tree and soon got stuck in the resin. As time passed, the resin solidified, turning into a fossil like dinosaur bones, and the mosquito remained inside. The petrified wood resin, commonly known as "amber", carefully preserved the insect for millions of years, until one day it turned out to be in the hands of scientists of Jurassic Park. Thanks to modern technology, they extracted the surviving blood from it and – bingo! – Dinosaur DNA!
The film "Jurassic Park".
Scientists can get genetic material
If in our time it is possible to detect amber with a mosquito that has drunk dinosaur blood, then modern methods of genetics will be able to isolate the genetic material of this dinosaur from this droplet of blood. Then this genetic material can be amplified using PCR (polymerase chain reaction) and artificially copy the existing DNA sections.
One human cell contains 46 chromosomes, and the total length of DNA molecules (each chromosome contains one DNA molecule) is approximately 2 meters. It turns out that one chromosome is about 4.34 cm, each of these fragments contains an important genetic text, the "words" of which encode the work of tissues, heart, blood vessels, nerves, muscles, skin, and in part even behavior. What is the length of the dinosaur DNA molecule is still unknown to science, so in further explanations we will return to this figure – 4.34 cm to clearly explain why cloning dinosaurs is not as easy as in the Steven Spielberg film. And there are enough difficulties along the way.
The first problem: how to deal with DNA half-life (solved)
A serious problem is how to get a meaningful and orderly genetic text of a dinosaur. The half-life of DNA, and the genetic material is encoded by the deoxyribonucleic acid molecule, is 500 years. That is, 500 years will pass, and our 4.34 cm will be divided in half. Another 500 years will pass, and now we have chromosomes 1 cm long, and after 1.5 thousand years, scientists will have only a little more than 5 mm at their disposal.
Every few hundred years, a linear DNA molecule degrades into small fragments. If we assume that the length of human and dinosaur chromosomes is the same, then scientists will get 0.1 mm long DNA fragments from a mosquito. Moreover, no one knows exactly in what order these fragments should be connected to each other.
The good news is that this difficulty is surmountable. You will have to spend a dozen or two years on it, but with the help of the genome analysis method and modern sequencing technologies of a new generation, you can get the final version of the genetic text on a computer. However, in reality, scientists will have access to all the same fragments of 0.1 mm of genetic material. And then we move on to the next task: how to transfer virtual knowledge to a physical environment?
The second problem: how to organize synthesis (almost unsolvable)
Let's say the DNA length of one dinosaur cell is the same two meters as that of a human. Therefore, these two meters, modeled on a computer, must be synthesized chemically, that is, to assemble a full-fledged DNA from the building blocks. At the same time, one step of synthesis is about 3.4 angstroms, and one angstrom is 10-10 m. Simply put, the synthesis will take an incredibly long time.
People have tried to artificially synthesize such texts. For example, American Craig Venter, one of the most famous geneticists in the world, was one of the first to completely sequence the human genome and asked the question: can we create artificial, fully synthetic life? Venter spent about a decade and a half on these works, during which he created an artificial DNA molecule consisting of 500 thousand steps – this is approximately 1.5 million angstroms [1]. And we will need to collect 2 meters for one molecule, that is, 20 billion angstroms.
Another difficulty at the synthesis stage is to decide how to properly package the synthesized DNA. In nature, DNA strands do not exist by themselves, they are packed into the cell nucleus, and the molecule is considered the ideal of compactness. That is, scientists must learn how to wind synthesized DNA strands on a kind of coils that will protect them from tearing. And this problem does not even have a theoretical solution at the moment.
The third problem: how to achieve biodiversity (completely unsolvable)
Let's assume that scientists have managed to recreate a genetic text, synthesize it, pack DNA into a cell and start the process of division. Then no less difficult questions begin, for example: how should the process of embryonic development go? And even if it is possible to solve this problem – a dinosaur egg will be hatched by some bird or it will be reproduced in laboratory conditions - the question of biological diversity arises.
In order for a species to exist and develop in nature, biodiversity is necessary. A few years ago, an analysis of the genetic material of the last mammoths that lived on Novaya Zemlya was published [2]. The data indicated their low viability, that is, even in the conditions of the existence of many individuals, living mammoths degenerated as a species. If people want to clone dinosaurs (or mammoths), they must artificially provide genetic diversity so that the population can exist and develop. How to create it? No one knows.
Literature
1. Daniel G. Gibson. Creation of a Bacterial Cell Controlled by a Chemically Synthesized Genome. 2010
2. Rebekah L. Rogers. Excess of genomic defects in a woolly mammoth on Wrangel island. 2017
About the author: Sergey Kiselyov – Doctor of Biological Sciences, Professor, Head of the Epigenetics Laboratory of the N. I. Vavilov Institute of General Genetics of the Russian Academy of Sciences.
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