By: Ivy Philips

Erwin Chargaff’s most notable discovery was finding out through experimentation was that in DNA, Adenine bonds with Thymine, and Cytosine bonds with Guanine. He discovered this because in DNA the amount of units for each one was equal to the other (A=T, C=G) This proved his theory and debunked the commonly accepted Tetranucleotide Hypothesis. This hypothesis stated that DNA was made of a random reoccurrence of GATC. Chargaff’s Rules also said that the amount of base pairs varied for different organisms. He stated that genetic material was carried by DNA and not by nucleic acids, as had been previously thought. This was a revolutionary breakthrough in science because he opened up new levels of science nobody had ever thought to study before. This theory introduced the idea genetic diversity. In 1952 Chargaff introduced his ideas to Francis Crick and James Watson. These scientists took Chargaff’s idea and built a model off of it. This model is called the Double Helix which was meant to display the way DNA is formed, and how the base pairs connect. Chargaff’s research and experiments forever changed the way scientists study and look at heredity and biology.

Francis Crick was a scientist from London, England. He worked on different project involving x-ray diffraction, biochemistry, chemistry, and physics. He was skilled in all of these subjects, but he most enjoyed the mysteries of genetic material and DNA. He was working at Cavendish Laboratory at Cambridge. In that lab he and his colleges were studying the structure of proteins using x-ray diffraction. While doing the lab he met James Watson. He and Watson established a great relationship in the lab. They both were interested in the same mysteries posed by DNA and genetics. Crick understood that should scientists know more about DNA, a model of some sorts must be established. This led his and Watson’s work on the double helix. They used x-ray diffraction to see the actual DNA and actual evidence from other scientists about base pairs and formed a reliable model. This model is know widely around the world and it is the most dependable model. Crick and Watson won the Nobel Prize in physiology/medicine in Even after his breakthrough findings and imminent success, he still continued to study genetics and how genetic material is coded throughout cells.

James Watson is a molecular biologist, geneticist, and zoologist. He is most famous for his work with Francis Crick on the DNA double helix model. Before he met Crick, though, he was working with the Phage Group. The Phage Group was a group of scientists led by Max Delbruck and Salvador Luria. This group conducted experiments on bacteriophages. Watson’s involvement in the Phage Group jumpstarted his interests in the structure of DNA. He later broke away from the Phage Group and began working with other scientists, but he frequently used Phages in his studies. In 1953 James Watson began doing research at the Cavendish Laboratory at Cambridge University. This is where he met Francis Crick. Francis was interested in the same things he was, so a close relationship was formed. They were both curious as to the shape of DNA and both believed that it could be reviled through x-ray diffraction. They made a model of DNA using a double helix. There findings were published and they later received a Nobel Prize in Physiology and Medicine. He continued working in science for a very long time. In 1990 he was appointed head of the Human Genome Project. He remained in this position for two years until he resigned in 1992 to work on another project.

Hermann Muller was an American geneticist. He is most famous for his work involving radioactive material and genes marked an incredible breakthrough in genetics and for Muller. Muller made a series of experiments involving various amounts of x-rays and genes. In his research and experiments there was a clear and defined connection between radiation and deadly mutations. These findings unnerved the science community because no findings of this nature had ever occurred before. After his discovery people started to be a bit more cautious of what wastes they put out and how radioactive material was handled. Muller was a very outspoken activist for the elimination of nuclear war and nuclear testing. In 1946 he was awarded the Nobel Prize in Physiology and Medicine for his discovery that mutations can be induced by radioactivity. After the world saw the effects the nuclear bombs had on Hiroshima and Nagasaki, they all listened to Muller. Today many precautions are made when it comes to nuclear testing and radioactive materials because of Hermann Muller’s findings.

Barbara McClintock is one of the world’s most renown cytogeneticists. A cytogeneticist is a person that studies the structure and function of a cell. In cytogenetics, chromosomes are thoroughly studied, too. McClintock started her career studying maize, which is a type of corn. Her main focus was to study the way maize cells reproduce. This allowed people to see how chromosomes changed inside the cell using microscopes. She discovered that in corn there are transposable elements. For years people had thought of DNA and chromosomes as ‘junk elements’. Barbara proved them all wring with her research on maize. Throughout her lengthy career she has been awarded numerous medals and honors for her work. In 1983 she was awarded the Nobel Prize in Physiology or Medicine.

Mid 1940s Chargaff’s rules 1926 Hermann Muller Early 1950s Francis Crick Early 1950s James Watson 1940s Barbara McClintock *Note: All of these scientists continued there work for a long time, so it is hard to place their years of ‘most activity’ on a time line. This is when they began to get recognition for their ideas/work or published them.