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In a ground-breaking experiment conducted in 1928, Frederick Griffith proved that there was a transformative principle in bacterial genetics. He proposed the idea that information might somehow be transmitted between several bacterial strains. Griffith employed the type III-S and type II-R strains of Pneumococcus bacteria for this study. Griffith first demonstrated that mice injected with III-S died in the first stage of the transforming principle experiment, but mice injected with II-R lived and displayed few symptoms. The following stage revealed that the mice all survived when given injections of type III-S that had been heated to death, proving that the bacteria had been rendered ineffective. The final stage of the experiment, in which mice were injected with a mixture of heat-killed III-S and live II-R, revealed the most fascinating results. Oddly enough, all of the mice died, proving that some type of information had been transferred from the dead type III-S to the living type II-R.

Sources
1. Rasmussen, F. N. (2021, February 4). Frederick N. Griffith, expert in corneal transplantation who founded Maryland Eye Bank, dies. Capital Gazette. Retrieved October 11, 2022, from https://www.capitalgazette.com/maryland/bs-md-ob-frederick-griffith-20210204-fsejd3v7w5d5ldtpavr7m26nre-story.html
2. Transforming Principle. Transforming Principle - Griffith's Experiment About Genetics. (n.d.). Retrieved October 11, 2022, from https://explorable.com/transforming-principle

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The team lead by Oswald Avery made the discovery that DNA carries the chemical code for life and transmits instructions from one generation of organisms to the next.  In a   publication that described the discovery that became known as the Avery-MacLeod-McCarty experiment, Avery and his coworkers reported their discovery. In reality, the experiment had more than a decade's worth of research. Oswald Avery's group demonstrated that DNA was the "transforming principle" in a simple experiment. DNA was able to change another strain of bacteria when it was isolated from one strain and transfer traits to the other strain. Hereditary information was carried by DNA. With DNA being the hereditary molecule, one of the most fascinating phases of DNA science the study of DNA structure and function began.

Sources
1. Cobb, M. (2014, January 20). Oswald Avery, DNA, and the transformation of biology. Current Biology. Retrieved October 11, 2022, from https://www.sciencedirect.com/science/article/pii/S0960982213015157
2. Home. Famous Scientists. (n.d.). Retrieved October 11, 2022, from https://www.famousscientists.org/oswald-avery/
3. Oswald Avery (c.1930) :: CSHL DNA learning center. Cold Spring Harbor Laboratory DNA Learning Center. (n.d.). Retrieved October 11, 2022, from https://dnalc.cshl.edu/view/15674-Oswald-Avery-c-1930-.html
4. Oswald Avery. FlowVella. (n.d.). Retrieved October 11, 2022, from https://flowvella.com/s/1068/Oswald-avery

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Erwin Chargaff initially observed that DNA, whether it was extracted from a plant or an animal, contained the same amounts of adenine, thymine, cytosine, and guanine. Chargaff found that in DNA, the ratios of adenine to thymine and guanine to cytosine are equal. This parity is obvious in the final DNA structure. The chemical pairings that make up the double helix were revealed by these equalities. Additionally, he discovered that different species have different amounts of guanine, cytosine, adenine, and thymine, suggesting that DNA and not protein may be the genetic building block for life. DNA's structure and replication mechanism were discovered thanks to Erwin Chargaff's research. It is extremely credible that DNA was genetic material given his finding that DNA differs from species to species.

Sources
1. Chargaff's ratios, 3D animation with narration :: CSHL DNA learning center. Cold Spring Harbor Laboratory DNA Learning Center. (n.d.). Retrieved October 11, 2022, from https://dnalc.cshl.edu/view/15495-Chargaff-s-ratios-3D-animation-with-narration.html
2. Erwin Chargaff. National Science and Technology Medals Foundation. (2020, July 31). Retrieved October 11, 2022, from https://nationalmedals.org/laureate/erwin-chargaff/
3. Science Photo Library. (n.d.). Portrait of biochemist Erwin Chargaff - stock image - H403/0113. Science Photo Library. Retrieved October 11, 2022, from https://www.sciencephoto.com/media/223952/view
4.Home. Famous Scientists. (n.d.). Retrieved October 11, 2022, from https://www.famousscientists.org/erwin-chargaff/

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James Watson & Francis Crick - 1951-1953

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James Watson & Francis Crick - 1951-1953

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James Watson and Francis Crick's discovery of the double helix, the twisted-ladder structure of deoxyribonucleic acid (DNA), in 1953 was a turning point in science and gave rise to the field of molecular biology, which is concerned with understanding how genes regulate the chemical reactions that take place inside of cells. Their discovery quickly led to revolutionary understandings of the genetic code and protein synthesis. It contributed to the development of new scientific techniques in the 1970s and 1980s.  significant scientific advancements nowadays, all have origins in Watson and Crick's work. The double helix has reshaped biology, as well has become a cultural icon. Early in their careers, Crick and Watson understood that the main challenge in molecular biology was to fully understand the three-dimensional arrangement of the gene. Heredity and reproduction could not be comprehended without it. It was Watson and Crick's responsibility to combine the crucial but seemingly unrelated findings of other researchers about the structure of DNA into a theory of genetic transfer.

Sources
1. National Institutes of Health. (n.d.). The discovery of The double helix, 1951-1953 | Francis Crick - profiles in Science. U.S. National Library of Medicine. Retrieved October 11, 2022, from https://profiles.nlm.nih.gov/spotlight/sc/feature/doublehelix
2.A. Barrington Brown, © G. & C. C. P. L. (n.d.). Crick & Watson with their DNA model in 1953 - stock image - H400/0041. Science Photo Library. Retrieved October 11, 2022, from https://www.sciencephoto.com/media/222785/view

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Beginning in 1951, Alfred Hershey and Martha Chase carried out a series of investigations that came to be known as the Hershey-Chase experiment which supported the conclusions reached by Avery and his colleagues. At the Carnegie Institution of Washington at Cold Spring Harbor, New York, Hershey conducted research on viruses. He researched bacteria-infecting viruses, known as bacteriophages or phages. In 1950, Chase was hired as Hershey's research technician. At the Carnegie Institute of Washington Alfred Hershey and Martha Chase carried out a series of experiments in 1951 and 1952 that proved genes were made of deoxyribonucleic acid (DNA.)  They performed their experiments on bacteriophages, they did their tests, which came to be known as the Hershey-Chase experiments. The Waring Blender experiment, the most well-known Hershey-Chase experiment, provided solid proof that genes were composed of DNA.

Sources
1. The Embryo Project Encyclopedia. The Hershey-Chase Experiments (1952), by Alfred Hershey and Martha Chase | The Embryo Project Encyclopedia. (n.d.). Retrieved October 11, 2022, from https://embryo.asu.edu/pages/hershey-chase-experiments-1952-alfred-hershey-and-martha-chase
2. Pictures and Illustrations. Martha Chase and Alfred Hershey. 1953. - pictures and illustrations - Linus Pauling and the race for DNA: A documentary history. (n.d.). Retrieved October 11, 2022, from http://scarc.library.oregonstate.edu/coll/pauling/dna/pictures/portrait-hersheychase.html

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Rosalind Franklin made a major contribution to the knowledge about DNA. In 1953, at King’s College London the discovery of the structure of DNA was made possible by her X-ray diffraction work. She created the famous Photo 51 which showed the double-helix structure of deoxyribonucleic acid, or DNA. DNA is a molecule that contains the genetic instructions for the development of all living organisms. Dr. Franklin had a Ph.D. from Cambridge and experience in X-ray diffraction in Paris. She joined John Randall's lab at King's in 1950. There, she demonstrated that the DNA molecule could exist in two forms, A and B, by adjusting the water concentration of the DNA sample.

Sources
1. Rosalind Franklin University. (2022, August 29). Retrieved October 11, 2022, from https://www.rosalindfranklin.edu/
2. Nature Publishing Group. (n.d.). Nature news. Retrieved October 11, 2022, from https://www.nature.com/scitable/topicpage/rosalind-franklin-a-crucial-contribution-6538012/
3. Public Broadcasting Service. (2022, July 26). American Masters: Decoding Watson ~ James Watson on X-ray crystallographer Rosalind Franklin. PBS. Retrieved October 11, 2022, from https://www.pbs.org/wnet/americanmasters/american-masters-decoding-watson-james-watson-on-x-ray-crystallographer-rosalind-franklin/10930/