Gregor Medel, was known as the "father of modern genetics" he was responsible for discovering the basic principles of heredity, through the use of his monastery garden, through his famous pea experiment he discovered that genes come in pairs and are inherited in distinctive units.
Friedrich Miescher was the first person to work on DNA. In 1869 he found DNA when working on leucocytes, while investigating the protein cells he found unexpected properties that did not match those of proteins. He originally called DNA "nuclein". At this point of the time there was little or no research on DNA.
Fredrick Griffith in 1928 performed an experiment demonstrating that bacteria is capable of transferring genetic information this is called transformation. In the experiment he used mice, no- virulent/ rough strain and virulent/smooth strain to see what condition the mice would die under if injected with the strains. At this point of time the research of DNA was up to H. Muller's x-rays that show induce mutations in a dose dependent fashion.
Oswald Avery was in the field of immunochemistry he was the first molecular biologist and a pioneer in this field. He is most known for his experiment that isolated DNA as the material of which genes and chromosomes are made. Avery found that the transformation of bacteria was due to DNA, when scientists previously thought traits were carried by proteins.
McClintock discovered transposition and used this information to show that genes are what are responsible for turning physical characteristics on and off. She worked on developing theories to show the suppression and expression of genetic information from one generation of maize plants to the next.
Erwin Chargaff in 1950 discovered two rules to prove that DNA had a double helical structure. The 1st rule is that DNA had a equal percentage of adenine to thymine and equal percentage of guanine to cytosine. The 2nd rule is adenine and thymine are always paired and can't be cross paired, the same with guanine and cytosine. At the time the research of DNA was at the point where people had just proven that genic material can be transferred between bacterial cells and DNA passes physical and mental characteristics through different generations.
Rosalind Franklin in 1951 she took x-rays of diffraction images of DNA that showed the helical form of the molecule. Her discovery helped Watson and Crick from their model of DNA. At time the research was up to Chargaff rules on how DNA has a double helical structure.
Maurice Wilkins originally studied biological molecules like DNA and viruses using microscopes. However, in 1951 he started working with Franklin producing x-rays of DNA, which helped Watson and Crick develop their model of DNA. The research was up to Chargaff rules at the time.
James Watson and Francis Crick worked together in 1953 to build the first three dimensional model of a DNA structure which helped other scientist understand DNA more thoroughly. At this point in time the research on DNA was up to Chargaff rules about DNA having a double helical structure.
Nirenberg was a young biochemist that discovered the first "triplet" a sequence of three bases of DNA that code for one of twenty amino acids, that have the function of being somewhat as the building blocks of proteins.
Frederick Sanger found that DNA contains thousands of small chemical units called nucleotides. He developed techniques for the sequencing of nucleotides. BY 1977 he sequenced approximately 5000 nucleotides along one strand of DNA from a bacterial virus. At this point of time the research for DNA was up to the first structure by Cohen and Boyer of recombinant DNA.