Strongest evidence that DNA is genetic material comes from:

Options

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

Answer

To determine the strongest evidence that DNA is the genetic material, we can analyze the options provided and refer to historical experiments that contributed to our understanding of DNA.

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the strongest evidence that supports the idea that DNA is the genetic material.

2. **Reviewing the Options**:
- **Chromosomes contain DNA**: While this is true, it does not directly prove that DNA is the genetic material.
- **Transformation of bacterial cells**: This refers to the process where bacteria take up DNA from their environment, which was notably demonstrated in Griffith's experiment.
- **DNA is present in the nucleus**: This is a characteristic of eukaryotic cells, but it does not serve as direct evidence of DNA being the genetic material.
- **DNA is not present in cytoplasm**: This statement is incorrect as DNA can be found in the cytoplasm of prokaryotic cells (like bacteria).

3. **Identifying Key Experiments**: The most significant evidence comes from Frederick Griffith's experiment in 1928, which demonstrated the process of transformation in bacteria. He showed that non-virulent bacteria could become virulent when exposed to heat-killed virulent bacteria, suggesting that some "transforming principle" was responsible for this change.

4. **Understanding Transformation**: In Griffith's experiment, the non-virulent bacteria took up DNA from the dead virulent bacteria, leading to a change in their phenotype. This indicated that DNA could transfer genetic information between cells.

5. **Conclusion**: Based on the analysis, the strongest evidence that DNA is the genetic material comes from the transformation of bacterial cells, as demonstrated in Griffith's experiment.

### Final Answer:
The strongest evidence that DNA is genetic material comes from the **transformation of bacterial cells**.

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