Which statement is not true for the base ratio of DNA ?

Options

A. Base ratio is constant for a given species.
B. Base ratio is variable for different species.
C. Base ratio does not depend on age of organism .
D. Base ratio is different for different tissues of organism.

Answer

To determine which statement is not true for the base ratio of DNA, we need to analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Base Ratio in DNA**:
- DNA is composed of four bases: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C).
- The base pairing rules state that A pairs with T and G pairs with C. This means that the amount of A is equal to T, and the amount of G is equal to C.

2. **Analyzing the Statements**:
- **Statement A**: "Base ratio is constant for a given species."
- This statement is true. The base ratio (A:T and G:C) remains constant for a specific species.

- **Statement B**: "Base ratio is variable for different species."
- This statement is also true. Different species can have different base ratios.

- **Statement C**: "Base ratio does not depend on the age of the organism."
- This statement is true. The base ratio remains the same regardless of the age of the organism.

- **Statement D**: "Base ratio is different for different tissues of the organism."
- This statement is false. The base ratio is consistent across all tissues in an organism. The DNA composition does not change from one tissue to another.

3. **Conclusion**:
- The statement that is not true regarding the base ratio of DNA is **Statement D**: "Base ratio is different for different tissues of the organism."

### Final Answer:
The statement that is not true for the base ratio of DNA is **D**: "Base ratio is different for different tissues of the organism."

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