One day while experimenting on inheritance and genetics on peas, Mendel discovered that the transition between peas is like that in humans and their children. He explained that heredity is transmitted in separate parts. The understanding that genes remain the same even if the characteristics of parents appear to merge in their children. He described the unit of heredity as a particle that does not change when passed onto offspring.
Thomas hunt Morgan
Thomas Hunt Morgan had become interested in species variation, and in 1911, he established the "Fly Room" at Columbia to determine how a species changed over time. For the next 17 years, in a Morgan and his students did ground-breaking genetic research using Drosophila melanogaster, fruit flies. Thomas Hunt Morgan developed the ideas, and provided the proof for the chromosomal theory of heredity. He did this by conducting experiments in the “fly room” where he demonstrated that the behaviour of chromosomes can explain inheritance he also discovered that genes are located linearly along chromosomes.
Phoebus Levene was an American biochemist who studied the structure and function of nucleic acids. He characterized the different forms of nucleic acid, and found that DNA contained adenine, guanine, thymine, cytosine, deoxyribose. Not only did Levene identify the components of DNA, he also showed that the components were linked together in the order phosphate-sugar-base to form units. He called each of these units a nucleotide.
In the late 1940’s Erwin Chargraff demonstrated that the bases of DNA are equal, there is an A for every T and a C for every G. He showed that even though different organisms have different amounts of DNA, the amount of adenine always equals the amount of thymine. The same goes for the pair guanine and cytosine.
The first picture of DNA was taken in May of 1952 by Rosalind Franklin of her student Raymond Gosling. Photograph 51 is the nickname given to the X-ray diffraction image DNA taken at King's College London. The technique would have been a very painstaking and time-consuming process. Franklin and Gosling used a very pure form of DNA and they became expert in pulling it into strands for analysis. Photo 51 became a crucial data source that led to the development of the DNA model and confirmed the prior suspected double helix structure of DNA.
James Watson and Francis Crick
James D Watson and Francis Crick on April 2, 1953, proposed that DNA was a double-helix structure, not a triple stranded structure as had been previously thought. The discovery in 1953 of the double helix, the twisted-ladder structure of DNA, by James Watson and Francis Crick marked a milestone in the history of science. Watson and Crick made their proposal based on the research of many other scientists and credited those pioneers respectfully. Such research included the crucial X-ray image “Photo 51" from Rosalind Franklin in 1952, as well as her more clarified DNA image with Raymond Gosling, Maurice Wilkins, Alexander Stokes, and Herbert Wilson and base-pairing chemical and biochemical information by Erwin Chargaff.
The Human Genome Project was an international scientific research project with the goal of determining the sequence of nucleotide base pairs that make up human DNA. It was also planned to identify and map all the genes of the human body. It remains the world's largest collaborative biological project. After the idea was picked up in 1984 by the US government when the planning started, the project formally launched in 1990.
The project finished in April 15, 2003. With its 3 billion letters of DNA code, the book of the human genome is here at last, two years ahead of schedule, scientists announced that the human genome had been sequenced with an accuracy of 99.99 per cent. It was described as ‘the end of the beginning’.