Strongest evidence that DNA is genetic material comes from-

Options

A. Chromosomes contain cells
B. Transformation of bacterial cells
C. DNA is present in nucleus
D. DNA is not present in cytoplasm

Answer

**Step-by-Step Solution:**

1. **Understanding Genetic Material Requirements**: For any substance to be considered genetic material, it must fulfill certain criteria. These include:
- The ability to self-replicate.
- The capacity to store and transmit genetic information necessary for the synthesis of proteins and enzymes.
- The potential to undergo mutations.
- The presence in chromosomes.

2. **Identifying the Key Experiment**: The strongest evidence that DNA is the genetic material comes from the experiments conducted by Frederick Griffith in 1928. This experiment is known as the "transforming principle" experiment.

3. **Overview of Griffith's Experiment**:
- Griffith worked with two strains of the bacterium *Diplococcus pneumoniae*: the S-strain (smooth, virulent) and the R-strain (rough, non-virulent).
- When the S-strain was injected into mice, the mice died due to the virulence of the bacteria.
- The R-strain, when injected, did not harm the mice, and they survived.
- Griffith then injected heat-killed S-strain bacteria into mice, which also survived.

4. **The Transforming Experiment**:
- Griffith mixed heat-killed S-strain bacteria with live R-strain bacteria and injected this mixture into mice.
- Surprisingly, the mice died after this injection, indicating that something from the heat-killed S-strain had transformed the R-strain into a virulent form.

5. **Conclusion of the Experiment**: Griffith concluded that a "transforming principle" from the heat-killed S-strain had been transferred to the R-strain, enabling it to produce a smooth polysaccharide coat, which is characteristic of the virulent S-strain. This transformation indicated the presence of genetic material, which was later identified as DNA.

6. **Final Assertion**: Therefore, the strongest evidence that DNA is the genetic material comes from Griffith's transforming principle experiment with bacteria.

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