Which statement is not true for 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 an 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. The base ratio refers to the proportion of nitrogenous bases in DNA, specifically the relationship between purines (adenine and guanine) and pyrimidines (thymine and cytosine).

### Step-by-Step Solution:

1. **Understanding Base Ratio**:
- The base ratio in DNA refers to the ratio of the nitrogenous bases. In DNA, adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C). The base pairing rules dictate that the amount of adenine is equal to thymine (A = T) and the amount of guanine is equal to cytosine (G = C).

2. **Evaluating the Statements**:
- **Statement A**: "Base ratio is constant for a given species."
- This statement is true. Each species has a specific base composition that remains constant.

- **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 age of organism."
- This statement is true. The base ratio remains constant throughout the life of the organism, regardless of age.

- **Statement D**: "Base ratio is different for different tissues of an organism."
- This statement is false. The base ratio does not vary between different tissues of the same organism; it remains constant.

3. **Identifying the Incorrect Statement**:
- After evaluating all the statements, we find that **Statement D** is the one that is not true regarding the base ratio of DNA.

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