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> The history of DNA Issue: 2009-1 Section: Biology



Today genetics is a source of great hope, in particular for medicine that is carrying on a battle against cancer. The progress in the field of genetics and medicine is the result of many scientists’ work.

It all started about two hundred years ago...

An abbot from the Czech Republic, formerly Austro-Hungarian Empire, Gregor Mendel, studied the transmission of hereditary features cultivating sweet peas.

Gregor Mendel was born in 1822 in a farmer’s family. He was an accurate and meticulous searcher. He was an expert in physics and in maths; he was one of the first scientists to apply Maths on Biology.

In 1866 Mendel showed that parents passed some hereditary factors to their children. Mendel studied the sweet peas plants because they were simpler for the cultivation and because of their great variety.

Beginning his experiments, Mendel prevented flower self-pollination by removing the flower stamens before the pollen was produced, so that the female individual developed.

After that, he strewed this flower with the pollen from another flower; so the flower produced some pea seeds that were planted. From the seeds a new sort of plant was born.

After many experiments, Mendel formulated three laws:


The first law or Law of the dominance says that hereditary traits are determined by some internal factors that are in the couple. Each organism had different traits that Mendel divided into two groups, recessive and dominant. When paternal gametes and two maternal gametes are united, they inherit both factors. However, the dominant factor masks the recessive one for the first generation (hybrid) which disappears and appears only in the future generation. If they are inherited together, the dominant character is expressed while the other one, the recessive, is not seen.


The second law or Law about the disjunction of the characters says that in the second generation, the character appears in a ratio of ¼ of one parent, in a ratio of ¼ the other parent and the rest is constituted by a hybrid.


The third law or Law about the independence of the characters says that from the crossbreed of two individuals with different characters, other individuals originate and the characters pass independently from one generation to the next.

Example: between yellow and smooth peas and green and wrinkled peas, we obtain in the first generation some yellow and smooth peas (dominant factor).

Crossing these individuals, we get a second generation:

9/16 of yellow and smooth peas;

3/16 of yellow and wrinkled peas;

3/16 of green and smooth peas;

1/16 of green and wrinkled peas.


The results of his research were not understood by the scientists and the research remained unknown for many years.

For this reason, in 1870 he left his studies. He died in 1884 without his search being recognized. Only in 1900 some scientists confirmed Mendel’s assumptions; they repeated his experiments. In 1930 his laws were understood, accepted and used to explain some phenomena, such as the genetic and the evolution factors.

After Mendel, there was Theodore Avery Oswald, born in Halifax. He was a doctor and a bacteriologist the first to prove that the factor responsible for the heredity transmission of features is not a protein, but a nucleic acid called DNA.

In 1952 an Austrian biochemist, named Chargaff, devoted himself to his study on the structure and on the function of the nucleic acids. He discovered regularity in the pairing of the nitrogenous bases that are Adenine, Thymine, Guanine and Cytosine. The nitrogenous bases are made of carbon, oxygen, nitrogen and hydrogen.

He enclosed his studies in one law called Law of Chargaff, where he asserted that adenine is always paired with thymine and the guanine with cytosine.

Rosalind Franklin was an English chemist and physicist. She was born in London on 25th July 1920 in a rich family of bankers. In 1951 she worked at King’s College, where she had a hard time because of the bad relations with her colleagues, rivalries and ambitions, but especially due to the strong male chauvinism that tended to separate women from men.

She studied the molecules according a new technique by herself called x-ray crystallography and thanks to it, she succeeded in defining the DNA structure taken from a calf’s thymus. She put together the photos and notes of her notebook, and she said that the DNA is formed by two distinct chains. Besides the study of the biological molecules, she also studied the structure of the carbon.

The new technique, the x-ray crystallography, allowed her to take photos of constituents of all living and non living beings, even the atoms. The photos and the notes of Rosalind Franklin allowed Watson and Crick to represent DNA. No recognition was given to Rosalind Franklin, the woman that allowed through the x-ray crystallography the most important and the greatest scientific revolution in the XX century. Rosalind Franklin died from an ovarian cancer when she was 38 years old.

James Watson was an American scientist and Crick was a French physicist.

They also worked at the Medical Research Council in London, where Franklin and Wilkins were already working.

Between the two scientists, there was not a good relationship because Wilkins considered Franklin his collaborator, while she felt independent. Indeed they had established a relationship of non-communication.

Wilkins often complained with Watson and Crick about the woman, saying that she hampered his work.

The three men, in private, called her the dark lady. Watson and Crick took advantage of the bad relationship that there was between the two collaborators so they stole Franklin’s notes and photos, without giving her any time to study what she had done and certainly, in a short time she would have reached the same results of the two scientists. They used Franklin’s notes that were pictures and x-ray diffractogram, without feeling obliged to cooperate either with her or with Wilkins. In 1952 Watson and Crick affirmed the double helix DNA structure that appears like a double helix held together by hydrogen ties between the bases, forming a kind of spiral staircase. After having finished preparing the thesis on the DNA structure, Watson decided to make a physical model, that is a construction of iron wires and shapes of cardboard, as Pauling had made. So Watson and Crick built models until all their information was satisfied. They presented their work to Bragg who wrote an article in a scientific magazine that made them famous. In 1962 Watson and Crick received the Nobel Prize for medicine.

In 1972, a U.S. biologist named Paul Berg was the first to unite two molecules of DNA from two different organisms to make a hybrid with the name of recombinant DNA. He isolated a single gene to be transferred into a living organism, in order to study its behaviour. Thanks to his studies the progress in genetic engineering went on promoting the development of new pharmaceuticals, such as insulin and the growth hormone. He managed to get the Noble Prize in 1980.


A recombinant DNA is created by combining DNA sequences that would not normally occur together, to code or to alter different traits for a specific purpose.

At the end of all these studies it was concluded that the DNA or DeoxyboNucleic Acid is the hereditary material of every living individual.

The DNA is situated in the core of the cells. It is constituted by a spiral at double screw propeller, formed by a sequence of nucleotides; a phosphate group, one molecule of sugar and one molecule of nitrogen basic from every nucleotide. The basic nitrogens are: adenine, thymine, guanine, cytosine divided into purine (adenine and guanine) and pyrimidine (cytosine and thymine).

Chargaff discovered the pairing among them and called it complementary. Thanks to the discovery by Chargaff scientists arrived to the conclusion that the DNA is capable to duplicate.

Each helix of the DNA is used as a template for the duplication. The duplication is important for the cellular division.

Conclusion: old scientists gave the men of today an input to deepen the studies in the DNA and in its structure. In the end, we can say than the DNA study has concerned some generations and it continues, because it is an interesting subject and it is very important to help ill people and to prevent some genetic diseases



to the kind teacher Francesca Pollicino for her help and encouragement



  • Laura Barberis e Marika De Acetis, Gregor Mendel,, Patrizia Picchi, torinoscienza, Torino, 28/03/01;
  • Carlo Ceruti, L’intuizione vincente,, Aldo Franco De Rose, chicmedicina, Liguria, 02/10/03;
  • Laura Barberis e Marika De Aceis, Watson e Crick,, Patrizia Picchi, torinoscienza, Torino, 20/03/03;
  • Redazione di Psicolinea, Rosalind Franklin, Proietti, Psicolinea, Ancona, 22/11/08;
  • Laura Barberis e Marika De Acetis, Rosalind Franklin,, Patrizia Picchi, Torinoscienza, Torino, 30/04/04.