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KEY CONCEPT DNA was identified as the genetic material through a series of experiments.

KEY CONCEPT DNA was identified as the genetic material through a series of experiments. Griffith finds a ‘transforming principle.’. Griffith experimented with the bacteria that cause pneumonia. He used two forms: the S form (deadly) and the R form (not deadly).

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KEY CONCEPT DNA was identified as the genetic material through a series of experiments.

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  1. KEY CONCEPT DNA was identified as the genetic material through a series of experiments.

  2. Griffith finds a ‘transforming principle.’ • Griffith experimented with the bacteria that cause pneumonia. • He used two forms: the S form (deadly) and the R form (not deadly). • A transforming material passed from dead S bacteria to live R bacteria, making them deadly.

  3. Avery identified DNA as the transforming principle. • Avery isolated and purified Griffith’s transforming principle. • Avery performed three tests on the transforming principle. • Qualitative tests showed DNA was present. • Chemical tests showedthe chemical makeupmatched that of DNA. • Enzyme tests showedonly DNA-degradingenzymes stoppedtransformation.

  4. Hershey and Chase confirm that DNA is the genetic material. • Hershey and Chase studied viruses that infect bacteria, or bacteriophages. • They tagged viral DNA with radioactive phosphorus. • They tagged viral proteins with radioactive sulfur. • Tagged DNA was found inside the bacteria; tagged proteins were not.

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