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Concept of Inheritance - Gregor (Johann) Mendel
Propounded works on trait inheritance, as an experiment he conducted on pea plants, led to the idea that characteristics can be transferred from one generation of a species to another of the same species. Although he couldn't tell what was responsible for this, he discovered that offsprings carried particular traits in preference to another; then he deduced that traits can be dorminant or recessive. He established the Laws of Mendelian Inheritance. -
DNA: The distinct molecule - Johannes Friedrich Miescher
Scientists wondered what could be the means for transferring inherited information. When they saw how the chromosomes duplicated and moved during cell division, chromosomes were quickly accepted as the means of transferring inherited information. Johannes Friedrich Miescher isolated various phosphate-rich chemicals, which he called nuclein (now nucleic acids), from the nuclei of white blood cells in 1869, paving the way for the identification of DNA as the carrier of inheritance. -
DNA: heredity transmitter - Oswald Avery, Colin McLeod & Maclyn McCarty
DNA was isolated as the material of which chromosomes were made. This was discovered because of the work propounded by Oswald Avery and his co-workers - Colin McLeod & Maclyn McCarty, where they elaborated on the Grififth's experiment of Bacterial transformation. -
Evidence about DNA - Erwin Chargaff
Through careful experimentation, Chargaff discovered two rules that helped lead to the discovery of the double helix structure of DNA. Chargaff's rules state that DNA from any cell of all organisms should have a 1:1 ratio of pyrimidine and purine bases; more specifically, that the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine, although Chargaff did not explicitly state this connection himself. -
DNA changes on heating - Linus Carl Pauling
Based on the structures of amino acids and peptides and the planar nature of the peptide bond, Pauling correctly proposed the alpha helix and beta sheet as the primary structural motifs in protein secondary structure. He said that these polypeptide chains were held by hydrogen bonds which could be broken by moderate heating. He suggested that a similar helical structure might explain changes that had been seen in DNA on heating. -
Discovery pathway - Maurice Wilkins & Rosalind Franklin
Maurice Wilkins & Rosalind Franklin were both working on X-ray diffraction of DNA. For a number of reasons, they stopped working together; an intense rivalry developed afterwards. Ever cautious, she wanted to eliminate misleading possibilities, so she worked out the positions of the groups in the DNA, relative to each other & the distances between them. This enabled her build a 2-stranded helical model for the DNA structure. Their overall effort contributed significantly in DNA modelling. -
Deducing the structure - James Watson & Francis Crick
Putting together information which they gathered from Rosalind Franklin & other scientific contributions to the discovery of the DNA structure, James Wtson & Francis Crick of the Cavendish Laboratory, Cambridge, alongside Maurice Wilkins (Rosalind's rival who gave them her work without her permission), assembled a model to depict the DNA structure. Watson discovered that two purines would be too small to be held together by hydrogen bonds and 2 pyrimidines would be too big.
