the history of the knowledge of dna n.
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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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what do we know
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 know1
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.
what do we know2
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.
what do we know3
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.
what do we know4
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?
what do we know5
What do we know?
  • So, it seemed logical that they hypothesized that protein was the genetic material.
slide8

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.