This page describes the modern biology scientists covered in Chapter 10 of the Modern Biology textbook.
Frederick Griffith
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Frederick Griffith studied the safe R and deadly S strands of pneumonia.
1. He put live R in mice. The mice lived.
2. He put live S in mice. The mice died.
3. He put heated/dead S in mice. The mice lived.
4. He put heated/dead S AND live R in mice. The mice died!?!
Somehow the safe R strands had been transformed into deadly S strands. He called this process transformation. This inspired other scientists to study transformation and led to the discovery of DNA.
(Transformation is the transfer of genetic material in the form of DNA fragments from one cell to another or from one organism to another.)
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Oswald Avery
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Oswald Avery wanted to know which part of the deadly S strand of pneumonia had gone into the safe R strand to kill the mice in Griffith’s experiment.
1. He heated/deactivated different parts of the S strand and put S strand in the mice with R strand.
2. Despite heating/deactivating the protease, lipase, RNA, etc., the mice still died.
3. Finally, he heated/deactivated the DNA, and the mice lived!
Avery discovered that DNA is what had transformed the safe R strand to be deadly like the S strand.
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Alfred Hershey and Martha Chase
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Martha Chase and Alfred Hershey knew that some traits (like eye color) are passed from parents to their children. They wondered if the information for those traits was in DNA or in a protein. They experimented with bacteriophages (viruses that attack bacteria to reproduce).
When they made a protein in the bacteriophage radioactive, the bacteria it attacked did not become radioactive. However, when they made the DNA in the bacteriophage radioactive, the bacteria it attacked did become radioactive.
They concluded that traits are passed from parents to children through DNA. DNA is what causes heredity. Heredity is the transmission of characteristics from parents to offspring.
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Rosalind Franklin and Maurice Wilkins
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British Rosalind Franklin and Kiwi Maurice Wilkins took X-ray diffraction photographs of DNA. These photographs helped scientists learn that DNA has a double helix shape.
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James Watson and Francis Crick
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During the 1950s, American James Watson teamed up with British Francis Crick to discover the structure of DNA. They studied the work of other scientists like the photographs taken by Franklin and Wilkins. Watson and Crick created the double helix model of DNA using the X-rays that Franklin and Wilkins had taken. The double helix looks like a spiral staircase. This model helped explain how DNA replicates.
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Erwin Chargaff
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American Erwin Chargaff noticed that the percentage of adenine always matched the percentage of thymine, ant that the percentage of cytosine always matched the percentage of guanine. This led him to conclude that these nucleotides pair up. Adenine (A) always goes with thymine (T). Cytosine (C) always goes with guanine (G).
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Beyond Scientists…
Visit our Science page for other science resources, and visit our Study Tools page for help with other subjects!
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