What results from the experiments of Frederick Griffith provided the strongest support for his conclusion that a transformation factor is responsible for heredity?

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Understand the context of Frederick Griffith's experiments: Griffith was studying two strains of the bacterium *Streptococcus pneumoniae*—a smooth (S) strain, which is virulent, and a rough (R) strain, which is non-virulent.

Recall the key experimental setup: Griffith injected mice with different combinations of these bacterial strains, including live R strain, live S strain, heat-killed S strain, and a mixture of live R strain with heat-killed S strain.

Focus on the critical observation: Mice injected with the mixture of live R strain and heat-killed S strain developed pneumonia and died, and live S strain bacteria were recovered from their bodies.

Interpret the results: The transformation of the non-virulent R strain into the virulent S strain suggested that some 'transforming factor' from the heat-killed S strain was transferred to the R strain, enabling it to acquire the virulent properties.

Conclude the significance: This experiment provided strong evidence that the 'transforming factor' was responsible for heredity, laying the groundwork for identifying DNA as the genetic material in later experiments.

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주요 개념

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Griffith's Experiment

Frederick Griffith conducted experiments in 1928 using two strains of Streptococcus pneumoniae: a virulent strain with a smooth appearance and a non-virulent strain with a rough appearance. He discovered that when he injected mice with heat-killed virulent bacteria mixed with live non-virulent bacteria, the mice developed pneumonia and died. This indicated that some 'transforming principle' from the dead bacteria was taken up by the live bacteria, transforming them into a virulent form.

Transformation

Transformation is a process in which a bacterium takes up foreign DNA from its environment and incorporates it into its own genome. In Griffith's experiment, the non-virulent bacteria acquired the genetic material from the heat-killed virulent bacteria, leading to a change in phenotype. This concept is fundamental in genetics as it demonstrates how genetic information can be transferred between organisms, influencing traits and characteristics.

Avery-MacLeod-McCarty Experiment

Building on Griffith's findings, the Avery-MacLeod-McCarty experiment in 1944 identified DNA as the 'transforming factor.' By treating the heat-killed virulent bacteria with enzymes that destroyed proteins, RNA, or DNA, they showed that only the destruction of DNA prevented transformation in the non-virulent bacteria. This provided strong evidence that DNA is the molecule responsible for heredity, supporting Griffith's initial conclusions about the transformation factor.