Which of the following is not true :-

Options

A. Operon hypothesis' was proposed by jacob and Monad
B. One gene-one enzyme' theory was proposed by Beadle and Tatum
C. Southern blotting' is used in DNA fingerprinting
D. Uracil bases remain present in DNA

Answer

To determine which of the statements is not true, we will analyze each option provided:

1. **Opron hypothesis was proposed by Jacob and Monod.**
- This statement is true. The Opron hypothesis, which explains the regulation of gene expression in prokaryotes, was indeed proposed by François Jacob and Jacques Monod based on their work with E. coli.

2. **One gene, one enzyme hypothesis was proposed by Beadle and Tatum.**
- This statement is also true. George Beadle and Edward Tatum proposed the one gene, one enzyme hypothesis, which states that each gene encodes a specific enzyme.

3. **Southern blotting is used in DNA fingerprinting.**
- This statement is true as well. Southern blotting is a technique used to detect specific DNA sequences and is commonly used in DNA fingerprinting to identify individuals based on their unique DNA patterns.

4. **Uracil bases remain present in DNA.**
- This statement is not true. In DNA, the nitrogenous bases are adenine, guanine, cytosine, and thymine. Uracil is found in RNA, not DNA. Therefore, this statement is incorrect.

Based on the analysis, the statement that is not true is: **"Uracil bases remain present in DNA."**

### Step-by-Step Solution:
1. **Identify the statements to evaluate.**
- List the statements given in the question.

2. **Evaluate the first statement about the Opron hypothesis.**
- Confirm that Jacob and Monod proposed this hypothesis and that it is true.

3. **Evaluate the second statement about the one gene, one enzyme hypothesis.**
- Verify that Beadle and Tatum are credited with this hypothesis, confirming it is true.

4. **Evaluate the third statement about Southern blotting.**
- Check that Southern blotting is indeed used in DNA fingerprinting, confirming it is true.

5. **Evaluate the fourth statement about uracil in DNA.**
- Recognize that uracil is not present in DNA, confirming this statement is false.

6. **Conclude which statement is not true.**
- Identify that the last statement regarding uracil is the one that is incorrect.