In one polyncleotide strand of a DNA molecule the ratio of `A+T//G+C` is `0.3`. What is the `A+G//T+C ` ratio of the entire DNA molecule ?

Options

A. 0.3
B. 0.6
C. 1.2
D. 1

Explanation

To solve the problem, we need to analyze the information given and apply Chargaff's rules regarding the nucleotide composition of DNA.

### Step-by-Step Solution:

1. **Understanding the Given Ratio**:
We are given that in one polynucleotide strand of a DNA molecule, the ratio of \( A + T \) to \( G + C \) is \( 0.3 \). This can be expressed as:
\[ \frac{A + T}{G + C} = 0.3 \]

2. **Expressing \( G + C \)**:
Let's denote \( G + C \) as \( x \). Then, we can express \( A + T \) in terms of \( x \):
\[ A + T = 0.3x \]

3. **Applying Chargaff's Rules**:
According to Chargaff's rules, in a double-stranded DNA molecule:
- The amount of adenine (A) is equal to thymine (T), and the amount of guanine (G) is equal to cytosine (C).
- Therefore, \( A + G = T + C \).

4. **Finding \( A + G \) and \( T + C \)**:
Since \( A + T = 0.3x \) and \( G + C = x \), we can find \( A + G \) and \( T + C \) using the relationships:
- Let \( A + G = y \) and \( T + C = z \).
- From Chargaff's rules, we know \( y = z \).

5. **Finding the Ratio \( \frac{A + G}{T + C} \)**:
Since \( A + G = T + C \), we can conclude that:
\[ \frac{A + G}{T + C} = 1 \]

6. **Final Answer**:
Therefore, the ratio \( \frac{A + G}{T + C} \) for the entire DNA molecule is:
\[ \boxed{1} \]