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The History of the Knowledge of DNA

The History of the Knowledge of DNA. What do we know?. Most people look somewhat like a mixture of their parents. They may have their father's nose or their mother's eyes, but in general, certain traits are passed on from one generation to the next. . What do we know?.

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The History of the Knowledge of DNA

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  1. The History of the Knowledge of DNA

  2. What do we know? • Most people look somewhat like a mixture of their parents. • They may have their father's nose or their mother's eyes, but in general, certain traits are passed on from one generation to the next.

  3. What do we know? • This is also the case with unicellular organisms. • This "genetic information" (the information which determines the traits which are passed down) must be stored somewhere in the cell, but just how or where eluded biologists for a long time.

  4. What do we know? • Eventually, microscopists noticed that during cell division, the sister chromatid pairs split, and each corresponding chromosome became part of a different daughter cell.

  5. What do we know? • This phenomenon suggested to biologists that the chromosomes must in some way contain the genetic information, especially since cells which obtained an abnormal number of chromosomes failed to function. • However, chemical analysis showed that the chromosomes were made of two major components: DNA (deoxyribonucleic acid) and protein.

  6. What do we know? • DNA was, at the time, thought to be a much simpler molecule than proteins, which scientists knew came in many varieties and combinations. • Which molecule was thought to be the carrier of hereditary information?

  7. What do we know? • So, it seemed logical that they hypothesized that protein was the genetic material.

  8. DRAWING 1: He first injected mice with a live strain of virulent (deadly) bacteria, and not to anyone's surprise, all of those mice died. • DRAWING 2: Then, he killed the virulent bacteria cells by heating them. • DRAWING 2: Mice injected with these heat-killed virulent bacteria did not die. • DRAWING 3: In another set of mice, Griffith injected a live non-virulent strain of bacteria, and these mice did not die, the result which Griffith expected. • DRAWING 4: Griffith injected a group of mice with both live non-virulent bacteria and heat-killed virulent bacteria. • DRAWING 4: In that group, some of the mice died. • Huh? • When Griffith examined those mice, he found live virulent bacteria in their blood. • What conclusion did he draw? • CONCLUSION: The genetic information in the heat-killed virulent bacteria survived the heating process and was somehow incorporated into the genetic material of the non-virulent strain to cause them to become virulent. • DRAWING 5: But Griffith knew that heat denatures protein. • CONCLUSION: He suggested that the genetic material must be something else. • However, his results did not specifically point to DNA as a possibility.

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