It has been 65 years since that distant 28 February 1953, when American biologist James Watson and British physicist Francis H.C. Crick, closeted within the walls of a laboratory at the University of Cambridge, in the United Kingdom, opened the doors to the mystery of the double helix of dna, deoxyribonucleic acid, the carrier of genetic information.

The great insight of the two researchers also came thanks to the contribution of biologist Maurice Wilkins and, above all, of biologist Rosalind Franklin, who was the first to produce an X-ray image of dna.

The fascination of discovery

The two researchers announced their discovery with the words: "We have discovered the secret of life" — a discovery that in 1962 earned Watson, Crick and Wilkins the Nobel Prize in Medicine. Rosalind Franklin received no recognition because, being a woman, she was not considered up to the mark — to such an extent that her work was used by the three researchers without her knowledge.

The double helix structure proposed by Watson and Crick was called the B form of dna and is considered the most stable form under physiological conditions. Two other variants exist: the A form and the Z form.

The spiral staircase with rungs

The structure of dna is often compared to a spiral staircase in which the uprights are the two polynucleotide chains and each rung is a pair of nitrogenous bases (adenine, thymine, cytosine and guanine), each belonging to one of the two polynucleotide chains. The two bases forming a rung are joined, according to Chargaff's rules, by hydrogen bonds: adenine forms two hydrogen bonds with thymine, while cytosine forms three hydrogen bonds with guanine. Dna thus has an alphabet made up of four "letters" (A, T, G, C) — the initials of the nitrogenous bases — which combine in triplets to form the genetic code. Within dna are contained the fundamental instructions for synthesising proteins through the decoding of the genetic code.

"The double helix has become an icon, an enormously powerful symbol of biology and of all science, because in reality no one expected the solution to the puzzle of genetic heritage to be so simple: discovering that everything is contained in a linear text, made up of an alphabet of just four 'letters', was like a bolt from the blue," explains geneticist Edoardo Boncinelli.

Scientific evolution

The Watson-Crick breakthrough has today led to major scientific innovations, from prenatal screening for pathogenic genes to the production of genetically modified organisms and plants, from the ability to identify human remains to the design of treatments for diseases such as aids and cancer, and the validation of evidence in criminal trials.

"The most important milestone was undoubtedly the discovery of restriction enzymes — those molecular tools that allow us to cut and stitch dna to make it do what we want," explains geneticist Giuseppe Novelli, rector of the University of Rome Tor Vergata.

The Crispr technique (Clustered Regularly Interspaced Short Palindromic Repeats), which allows us to correct dna, and related techniques now provide scientists with an unprecedented level of genetic editing accuracy. Potentially, the techniques can prevent thousands of conditions caused by specific inherited mutations. These include conditions such as sickle cell anaemia, cystic fibrosis and some cases of early-onset Alzheimer's.

"Genetic recombination marked a turning point. It made it possible, for example, to produce human insulin for diabetics using bacteria grown in the laboratory rather than pigs, but above all it paved the way for the two great innovations of the moment that will change our future: the Crispr technique, which will allow us to correct dna in an ultra-precise manner, eliminating many genetic diseases, and cell reprogramming, which has opened up new scenarios for regenerative medicine, consigning to the attic the idea of human cloning aimed at producing spare parts," Novelli added.

The other side of the coin

So far, so wonderful — but there is a "but". Genetic manipulation remains a minefield; there is the age-old problem of the unintended consequences of certain procedures, and the boundary between ethics and manipulation of the genetic makeup is a very fine one.

"Certainly, we will soon be able to modify the genome of our own species, to become healthier and longer-lived. The technologies are already available: it is we who are hesitating, because you cannot play around with human beings. All of this, however, gives me cause for hope — the outcome we will have from it will depend on how much good judgement we apply. We have called ourselves Homo sapiens: now we must prove that we truly are," commented Boncinelli.

Some experts, in an article published in the New York Times, point out how unregulated genetic engineering could lead to a new form of eugenics in which, for example, people with financial means can pay to have children with enhanced genetic traits. It therefore becomes a priority to define rules that take into account ethical, economic, social, safety and religious aspects, so as to ensure that we do not stray into unregulated and rather dangerous territory.

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