History of DNA

1859 - Charles Darwin publishes The Origin of Species

In 1859, Charles Darwin published The Origin of Species, changing the way many people viewed the world forever.

In 1831, Darwin had joined a five year scientific expedition. During his time away was influenced by Lyell's suggestion that fossils found in rocks were evidence of animals that had lived millions of years ago. The breakthrough came when he noted that the Galapagos Islands each supported its own variety of finch, which were closely related but had slight differences that seemed to have adapted in response to their individual environments.

On his return to England, Darwin proposed a theory of evolution occurring by the process of natural selection, which he then worked on over the following 20 years. The Origin of Species was the culmination of these efforts and argued that the living things best suited to their environment are more likely to survive, reproduce and pass on their characteristics to future generations. This led to a species gradually changing over time. Whilst his study contained some truth many areas such as the link between animal and human evolution are being shown to be untrue through new discoveries of ancient ancestors.

The book was extremely controversial, as it challenged the dominant view of the period that many people literally took that God had created the world in seven days. It also suggested that people were animals and might have evolved from apes this part of his work has been shown to be inaccurate. To Ponder; One must simply consider the fact that through thousands of years of evolution animals have the highest respect for their body yet people do not respect their bodies. The cheetah will go hungry rather than push itself beyond the point it can recover. If people had evolved from animals over millions of years the innate respect for their body would still be here today.

1866 - Gregor Mendel discovers the basic principles of genetics

In 1866, an unknown Augustinian monk was the first person to shed light on the way in which characteristics are passed down the generations. Today, he is widely considered to be the father of genetics. However, he enjoyed no such notoriety during his lifetime, with his discoveries largely passing the scientific community by. In fact, he was so ahead of the game that it took three decades for his paper to be taken seriously.

Between 1856 and 1863 Mendel conducted experiments on pea plants, attempting to crossbreed "true" lines in specific combinations. He identified seven characteristics: plant height, pod shape and colour, seed shape and colour, and flower position and colour.

He found that when a yellow pea plant and a green pea plant were bred together their offspring was always yellow. However, in the next generation of plants, the green peas returned in a ratio of 3:1.

Mendel coined the terms 'recessive' and 'dominant' in relation to traits, in order to explain this phenomenon. So, in the previous example, the green trait was recessive and the yellow trait was dominant.

In his 1866 published paper, Mendel described the action of 'invisible' factors in providing for visible traits in predictable ways. We now know that the 'invisible' traits he had identified were genes.

1869 - Friedrich Miescher identifies "nuclein"

In 1869, Swiss physiological chemist Friedrich Miescher first identified what he called "nuclein" in the nuclei of human white blood cells, which we know today as deoxyribonucleic acid (DNA).

Miescher's original plan had been to isolate and characterise the protein components of white blood cells. To do this, he had made arrangements for a local surgical clinic to send him pus-saturated bandages, which he planned to wash out before filtering the white blood cells and extracting their various proteins.

However, during the process, he came across a substance that had unusual chemical properties unlike the proteins he was searching for, with very high phosphorous content and a resistance to protein digestion.

Miescher quickly realised that he had discovered a new substance and sensed the importance of his findings. Despite this, it took more than 50 years for the wider scientific community to appreciate his work.

1900s - The Eugenics Movement

In the history of DNA, the Eugenics movement is a notably dark chapter, which highlights the lack of understanding regarding the new discovery at the time. The term 'eugenics' wasfirst used around 1883 to refer to the "science" of heredity and good breeding.

In 1900, Mendel's theories, which had found a regular statistical pattern for features like height and colour, were rediscovered. In the frenzy of research that followed, one line of thought branched off into social theory and developed into eugenics.

This was an immensely popular movement in the first quarter of the 20th century and was presented as a mathematical science, which could predict the traits and characteristics of human beings.

The darker side of the movement arose when researchers became interested in controlling the breeding of human beings, so that only the people with the best genes could reproduce and improve the species. It was often used as a sort of 'scientific' racism, to convince people that certain 'racial stock' was superior to others in terms of cleanliness, intelligence etc. It shows the dangers that come with practicing science without a true respect for humanity as a whole.

Many people could see that the discipline was riddled with inaccuracies, assumptions and inconsistencies, as well as encouraging discrimination and racial hatred. However, in 1924 it gained political backing when the Immigration Act was passed by a majority in the U.S. House and Senate. The Act introduced strict quotas on immigration from countries believed by eugenicists to have 'inferior' stock such as Southern Europe and Asia. When political gain and convenient science combine forces we are left even further from truth and a society that respects those within in. This is not too dissimilar from the tobacco industries of the 80’s and the sugar industries of the current decade.

With continued scientific research and the introduction of behaviourism in 1913, the popularity of eugenics finally began to fall. The horrors of institutionalized eugenics in Nazi Germany which came to light after the 2nd World War completely extinguished what was left of the movement.

1900 – Mendel's theories are rediscovered by researchers

In 1900, 16 years after his death, Gregor Mendel's pea plant research finally made its way into the wider scientific community.

The Dutch botanist and geneticist Hugo de Vries, German botanist and geneticist Carl Erich Correns and Austrian botanist Erich Tschermak von Seysenegg all independently rediscovered Mendel's work and reported results of hybridization experiments similar to his findings.

In Britain, biologist William Bateson became a leading champion of Mendel's theories and gathered around him an enthusiastic group of followers. Known as ‘Mendelians’, the supporters initially clashed with Darwinians (supporters of Charles Darwin's theories). At the time, evolution was believed to be based on the selection of small, blending variations whereas Mendel's variations clearly did not blend.

It took three decades for Mendelian theory to be sufficiently understood and to find its place within evolutionary theory.

1902 - Sir Archibald Edward Garrod is the first to associate Mendel's theories with a human disease

In 1902, Sir Archibald Edward Garrod became the first person to associate Mendel's theories with a human disease. Garrod had studied medicine at Oxford University before following in his father's footsteps and becoming a physician.

Whilst studying the human disorder alkaptonuria, he collected family history information from his patients. Through discussions with Mendelian advocate William Bateson, he concluded that alkaptonuria was a recessive disorder and, in 1902, he published The Incidence of Alkaptonuria: A Study in Chemical Individuality. This was the first published account of recessive inheritance in humans.

It was also the first time that a genetic disorder had been attributed to "inborn errors of metabolism", which referred to his belief that certain diseases were the result of errors or missing steps in the body's chemical pathways. These discoveries were some of the first milestones in scientists developing an understanding of the molecular basis of inheritance.

1944 - Oswald Avery identifies DNA as the 'transforming principle'

By the 1940s, scientists understanding of the principles of inheritance had moved on considerably - genes were known to be the discrete units of heredity, as well as generating the enzymes which controlled metabolic functions. However, it wasn't until 1944 that deoxyribonucleic acid (DNA) was identified as the 'transforming principle'.

The man who made the breakthrough was Oswald Avery, an immunochemist at the Hospital of the Rockefeller Institute for Medical Research. Avery had worked for many years with the bacterium responsible for pneumonia, pneumococcus, and had discovered that if a live but harmless form of pneumococcus was mixed with an inert but lethal form, the harmless bacteria would soon become deadly.

Determined to find out which substance was responsible for the transformation, he combined forces with Colin MacLeod and Maclyn McCarty and began to purify twenty gallons of bacteria. He soon noted that the substance did not seem to be a protein or carbohydrate but rather a nucleic acid, and with further analysis, it was revealed to be DNA.

In 1944, after much deliberation, Avery and his colleagues published a paper in the Journal of Experimental Medicine, in which they outlined the nature of DNA as the 'transforming principle'. Although the paper was not widely read by geneticists at the time, it did inspire further research, paving the way for one of the biggest discoveries of the 20th century.

1950 - Erwin Chargaff discovers that DNA composition is species specific

In 1944, scientist Erwin Chargaff had read Oswald Avery's scientific paper, which identified DNA as the substance responsible for heredity. The paper had a huge impact on Chargaff and changed the future course of his career. He later recollected, “Avery gave us the first text of a new language, or rather he showed us where to look for it. I resolved to search for this text. Consequently, I decided to relinquish all that we had been working on or to bring it to a quick conclusion”.

Chargaff was determined to begin work on the chemistry of nucleic acids. His first move was to devise a method of analysing the nitrogenous components and sugars of DNA from different species.

He subsequently submitted two papers to the Journal of Biological Chemistry (JBC) detailing the complete qualitative analysis of a number of DNA preparations. Despite the significance of the paper’s findings, the JBC was initially reluctant to publish it, illustrating the ignorance about nucleic acids amongst elite scientists at the time.

Chargaff continued to improve his research methods and was eventually able to rapidly analyse DNA from a wide range of species. In 1950, he summarised his two major findings regarding the chemistry of nucleic acids: first, that in any double-stranded DNA, the number of guanine units is equal to the number of cytosine units and the number of adenine units is equal to the number of thymine units, and second that the composition of DNA varies between species. These discoveries are now known as 'Chargaff's Rules'.

1952 - Rosalind Franklin photographs crystallized DNA fibres

Rosalind Franklin was born in London in 1920 and conducted a large portion of the research which eventually led to the understanding of the structure of DNA - a major achievement at a time when only men were allowed in some universities' dining rooms.

After achieving a doctorate in physical chemistry from Cambridge University in 1945, she spent three years at the Laboratoire Central des Services Chimiques de L'Etat in Paris, learning the X-Ray diffraction techniques that would make her name. Then, in 1951, she returned to London to work as a research associate in John Randall's laboratory at King's College.

Franklin's role was to set up and improve the X-ray crystallography unit at King's College. She worked with the scientist Maurice Wilkins, and a student, Raymond Gosling, and was able to produce two sets of high-resolution photographs of DNA fibres. Using the photographs, she calculated the dimensions of the strands and also deduced that the phosphates were on the outside of what was probably a helical structure.

Franklin's photographs were described as, "the most beautiful X-ray photographs of any substance ever taken" by J. D. Bernal, and between 1951 and 1953 her research came close to discovering the structure of DNA. Unfortunately, she was ultimately beaten to the post by Thomas Watson and Frances Crick.

The above image shows the original samples of DNA which were given to Maurice Wilkins by Swiss biochemist Rudolf Signer. PhD student Raymond Gosling then used the samples to produce the first crystals of DNA and, with Rosalind Franklin, used them for the next generation of X-ray images.