In modern day the substance is now known as deoxyribonucleic acid more commonly known as DNA. Miescher in the latter part of his life is credited with being the first to successfully extract DNA from another cell, with that cell being salmon sperm.
The next person to follow in line of genetic discoveries was Frederick Griffith, he is best known for the "Griffith Experiment"." It was one of the very first experiments credited with the discovery suggesting that bacteria is actually capable of transferring genetic information through the term known today as transformation. He infected several different mice with different strains of bacteria and exposed those mice to heat. Only one group of the mice survived and they were the mice infected with the "III-S " strain of bacteria. While this may not seem as big of a discovery compared to the previous discoveries mentioned, it is equally as important. .
Following the discoveries of Frederick Griffith, a man by the name of Phoebus Levene came along. Levene was a biochemist that specialized in the structure and function of nucleic acids. He is the first credited with deciphering the difference in DNA and RNA. Levene also found that within the DNA there were the chemicals adenine, guanine, thymine, cytosine and deoxyribose. In the year 1910 Levene is given credit for his "tetranucleotide hypothesis " which said that DNA is made up of equal amounts of adenine, guanine, thymine, cytosine and deoxyribose. It was later proven by the work of Erwin Chargaff that this was actually incorrect and that Levene's proposed idea of tetranucleotide structure was incorrect.
Following Levene's discoveries and everyone's previous to him, Erwin Chargraff came about in an era of genetics when scientists were attempting to create a model to replicate DNA. In the 40's Chargraff identified this pattern in four bases those being adenine, guanine, cytosine and thymine.
