DNA, the basic unit of inheritance, has a long history which takes us thousands of years back into the past. It is highly important to have apt knowledge of DNA. In its truest sense, our knowledge of DNA begins with the results of the experiment conducted by Gregor Mendel in the year 1857. He is known by the name of “Father of Genetics”. The study of genetics was further taken ahead by Friedrich Miescher upon his discovery of a substance which he called as nuclein in the year 1869. Later on, he progressed with his experimentations and discovered another material which was later known as the DNA. In the year 1889, his student Richard Altmann names the substance as nucleic acid. The existence of this particular substance was there only within chromosomes.
Another researcher, named as Frederick Griffith, performed an experiment in 1928. This experimentation led to the establishment of DNA as the basis of inheritance. The experimentation was done taking some mice and two different types of pneumonia. One of the forms of pneumonia was found to be virulent and the other one was non- virulent. On injecting the virulent organism into one of the mice it was seen that the mouse was dead. However, on injecting the non- virulent organism into another mouse, it survived. He further proceeded with the experiment by heating the virulent organism with the aim of killing it. As expected, the killed virulent organism did not produce any serious effect on the mouse, and as a result, it survived. In the next phase of his experiment, he injected a mouse with a heated and already killed virulent organism with along with a non- virulent one. But this time, the result was unexpected, the mouse was found to be dead. The death of the mouse made Griffith believe that the virulent organism would have passed some of its character to the other non- virulent organism. He hypothesized that this character was present within the inheritance molecule of the mouse. The method of passing off characteristics from one organism to another was known as transformation.
Another eminent scientist by the name of Oswald Avery further took forward the experiment of Griffith. His objective was to identify the particular inheritance molecule. He began his experiment almost 10 years after Griffith’s work on the same. He destroyed all the lipids, carbohydrates, proteins and ribonucleic acids of the virulent organism. He found that transformation occurred even after destroying all these important components of the cells. In the next phase, he destroyed deoxyribonucleic acid and found that the transformation has stopped. It made him reach to the conclusion that the inheritance material is the deoxyribonucleic acid.
In the year 1929, another researcher, Phoebus Levene of Rockefeller Institute, successfully identified the different components which make a DNA molecule. These components are four bases (Namely Adenine, Guanine, Cytosine and Thymine), Sugar and Phosphate. He further stated that the DNA molecules were linked with the help of fixed patterns of Phosphate- Sugar- Base. He concluded that all these components are nucleotides and DNA consists of chains of these nucleotides linked to each other with the help of phosphate groups. Further, he stated that these phosphate groups form the backbone of the entire molecule. However, his hypotheses that the chains are short and there was a repetition of fixed orders were proved to be false by Einar Hammersten and Tobjorn Caspersson who proved DNA as a polymer.
In order to improve their understanding of the DNA molecule, scientists constructed a model to understand the working and functioning of the DNA molecule. Erwin Chargaff discovered a definite pattern in the amount of the four different bases namely, Adenine, Guanine, Thymine and Cytosine. He took sample DNA from different molecules and discovered that amount of the Adenine was almost similar to that of Thymine, and the amount of Cytosine was similar to that of Guanine. It can be said in symbolic terms as G=C and A=T. This rule was later known as the Chargaff’s rule.
In the year 1952, the renowned bacteriologist, namely, Alfred Hershey and Martha Chase, his assistant conducted their experiment with some infected bacteria (these bacteria were very small, were infected with the virus and had an outer protein coat which surrounded the DNA). They knew that these viruses were responsible for the transfer of hereditary information. But they were unsure if the transferred information was actually protein or DNA. They decided to infect other sets of bacteria. Some of them had radioactive labelled proteins and others had radioactive labelled DNA. The results showed that the bacteria which were infected became radioactive from DNA. This led to the establishment of the fact that DNA is actually the hereditary molecule ("Interactives . DNA . History of DNA", 2016).
In order to enhance their knowledge about DNA, Maurice Wilkins and Rosalind Franklin developed crystal of DNA molecule. They decided to develop an X- ray film of DNA molecule in order to understand its working principle. They successfully obtained X- ray pattern of the same. The pattern looked like rungs which simulated a ladder. This made them state that DNA has a helical structure.
Then came about the most important discovery in the field of DNA made by Watson and Crick in the year 1953, they took the X-ray picture developed by Franklin and Wilkins and developed their own model. The model created by them has not undergone much change till date and is still the cornerstone. Their model consists of helical structures bound with the help of some small rungs. These rungs formed the base of the nucleotides. They also stated that Chargaff’s hypothesis held true in saying that Adenine and Thymine, Guanine and Cytosine were almost equal. They further stated that hydrogen bonds can form between two base pairs, in addition to that, each side is the complement of its opposite was also discovered by this duo.
(DNA Structure, 2016)
The world famous, Double Noble Prize winner Sanger, developed another breakthrough in the history of DNA. He developed the chain termination process of DNA sequencing. This method was also named as Sanger method later. In this particular method, fragments of DNA were produced, which were then separated on the basis of their size. Upon reading those fragments, scientific personnel can successfully figure out the accurate sequencing of the Adenine, Guanine, Cytosine and Thymine.
Genentech, the first genetic engineering company of the world which came into existence in the year 1977, became the first one to modify organisms at their genetic levels for producing the human hormones namely, somatostatin, insulin, and HGH or human growth hormone. Since then, molecular biologists have been utilising their knowledge of genetics for the production of many medicines and treatment of many diseases.
Then one of the latest discoveries in this field by Alex Jeffreys brought about a new milestone. He discovered DNA profiling. DNA profiling was first used for solving the murder mystery of Leicestershire in England. It opened a whole new world of research in the field of DNA (Mandal, 2012).
Kary B. Mullis, the Nobel Prize winner and a renowned biologist took a major step towards the history of DNA evolution. He published his first paper on the subject of Polymerase Chain Reaction (PCR). PCR stands for the process of producing innumerable strands of DNA from a minute amount in the least possible time. This method is been used till date for the diagnosis of hereditary diseases, paternity tests, diagnosing infectious diseases, forensic investigations, genetic cloning, and in several other science- related fields.
(Polymerase Chain Reaction, 2016)
The gene replacement therapy proved to be a boon for the medical world after it was first used in a 4- year- old patient with a rare disease called the SCID or Severe Combined Immunodeficiency disease. The girl was subjected to the gene replacement therapy procedure. Her white blood cells were removed from her bone marrow. In the labs, the white blood cells were subjected to a virus which helped in treating the defects in the damaged genes. Ultimately, these cells were restored in her body. This therapy, although, did not bring about a permanent cure, but did stabilise her condition for a considerably longer period of time. This milestone was achieved in the year 1990.
The Genetically Modified Crops became another important topic of discussion in the year 1993. Calgene, a biotech company in California grew the first genetically modified crops which were successful in gaining a license for human consumption by the United States FDA. The modification brought about in a tomato made it resistant to rotting (Bruening & Lyons, 2000). Since then, there have been many advances in this field and consumption of these crops have gained great momentum.
(Genetically Modified Crops, 2016)
5 July 1996, a day to remember in the history brought about the birth of the first cloned mammal known as the Dolly Sheep. The sheep was cloned with the help of cells extracted from an adult animal (Wade, 2013). Cloning is basically a process of producing identical copies of an organism. However, the principle of Cloning came under much debate when it was utilised for illegal purposes. The ethical implications of the concept are still debatable and require more detailed analysis and examination.
DNA and its related aspects have been of much interest since ages to all the people across the world. It has led to the generation of a lot of curiosities in the minds of the scientific professionals. A lot has been already discovered but still a huge ocean of knowledge yet to be acquired, is left in front of us. The developments in the field of genetics have benefitted the mankind to a great extent. More discoveries and inventions in this field can bring about further improvements and can help in bringing about more technological advancements for the benefit of the humanity. Scientists are working effortlessly towards the betterment and enhancement of our knowledge of DNA.
References
Bruening, G., & Lyons, J. (2000). The case of the FLAVR SAVR tomato. California Agriculture, 54(4), 6-7. Retrieved from http://californiaagriculture.ucanr.org/landingpage.cfm?article=ca.v054n04p6
DNA Structure. (2016). Retrieved from https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcRZZOnL9AS9XoxseLOSh-Gy0QAf5OnFWhwifIpEvKBgv4Ozy7zycg
Genetically Modified Crops. (2016). Retrieved from http://www.cesti.gov.vn/images/cesti/stinfo/Nam%202015/So8/0815_DT_BDG_Mi%20BT-H00.jpg
Interactives . DNA . History of DNA. (2016). Learner.org. Retrieved 20 March 2016, from https://www.learner.org/interactives/dna/history.html
Mandal, A. (2012). History of DNA Research. News-Medical.net. Retrieved 20 March 2016, from http://www.news-medical.net/life-sciences/History-of-DNA-Research.aspx
Polymerase Chain Reaction. (2016).
Wade, N. (2013). The Clone Named Dolly. The New York Times. Retrieved from http://www.nytimes.com/2013/10/14/booming/the-clone-named-dolly.html?_r=0
