Charles Darwin realises that all living organisms adapt to their individual's environments and changes accordingly by analysing the fossils found in rocks from million years ago. He then proposes the theory of evolution that occurred through the process of natural selection and the organisms that best suited to their environment are most likely survive for a long time and reproduce that adapted characteristic to their next generations. Darwin claim that this adapation ability that animals obtained ultimately lead to species gradually changing over time. This set a foundation for the discovery of DNA to be made.
Gregor Mendel was considered the father of genetics. Between 1863 and 1865, Mendel conducted several experiments regarding the crossbreed of pea plants in specific combinations. Through the experiment, he found out that when a yellow pea and a green pea were bred together, their offspring was always yellow. By this, Mendel discovered the term of 'recessive' and 'dominant' in relations to traits and genetics, and in this case, the green pea trait was recessive and the yellow pea trait was dominant. After his significant discovery, he published a paper describing a 'invisible' factor affecting the traits in a predicatable way, which is what we know today as genes.
In 1869, a Swiss physiological chemist Friedrich Miescher first identified what he called the 'nuclein' in the nuclei of human white blood cell. This nuclein is what we know today as deoxyribose acid (DNA).
Miescher was originally conducting an experiment to isolate and characterise the protein components within human white blood cells. He then came across a substance that had unusual chemical properties, which is deoxyribose acid. However, his discovery was not appreciated at the time.
By 1944, deoxyribose acid was identified as the 'transforming principle' within living organisms. Oswald Avery, an immunochemist at the Hospital of the Rockefeller Institute for medical research discovered that if a living but harmless form of pneumococcus was mixed with a lethal but inert form, the harmless bacteria transforms to become deadly. Avery was them determined to find out which substance was responsible for the transformation, he noticed that the substance was changed due to a nucleic acid, which is DNA.
Even though the paper he published regarding this discovery was not widely appreciated, it did inspire further research and paved ways for one of the most important discovery of 20th century.
Erwin Chargaff having read Oswald Avery's scientific paper that identified DNA as the substance responsible for heredity, conducted an experiment and devised a method of analysing the nitrogenous components and sugar of DNA in different species. He was also able to analyse the DNA from different species.
In 1950, he published a paper regarding his most important and significant finding regarding to the chemistry of nucleic acids.
1. In any double stranded DNA, the number of guanine units is equal to the number of cytosine. On the other hand, the number of adenine units is equal to the number of thymine units.
2. The composition of DNA varies across different speicies. This law is also known as the Chargaff's law.
Scientists James Watson and Francis Crick using the available X-ray data and model building of DNA structure at the time, they were able to solve the puzzle that had baffled scientists for decades,
The discovery of the structure of DNA was significant even up to this day and James Watson was awarded the Nobel Prize for physiology for this discovery