A mixture containing DNA fragments A,B,C and D, with molecular weights of `A + B = C,A gt B and D gt C`, was subjected to agarose gel electrophoresis. The positions of these fragments from cathode to anode sides of the gel would be
(a) D,C,A,B
(b) A,B,C,D
(c) C,B,A,D
(d) B,A,D,C

Options

A. D,C,A,B
B. A,B,C,D
C. C,B,A,D
D. B,A,D,C

Answer

To solve the problem of determining the positions of DNA fragments A, B, C, and D after agarose gel electrophoresis, we need to analyze the given information about their molecular weights and how they relate to each other.

### Step-by-Step Solution:

1. **Understanding the Relationships**:
- We are given that \( A + B = C \). This means that the combined weight of fragments A and B is equal to the weight of fragment C.
- We also know that \( A > B \) and \( D > C \). This indicates that fragment D is heavier than fragment C.

2. **Determining Relative Sizes**:
- From \( A + B = C \), we can infer that both A and B must be lighter than C. Therefore, \( C > A \) and \( C > B \).
- Since \( A > B \), we can conclude that A is heavier than B, but both are still lighter than C.
- Given \( D > C \), we can conclude that D is the heaviest fragment of all.

3. **Ranking the Fragments by Weight**:
- From the above relationships, we can rank the fragments based on their weights:
- D (heaviest)
- C (next heaviest)
- A (lighter than C but heavier than B)
- B (lightest)

4. **Understanding Gel Electrophoresis Movement**:
- In agarose gel electrophoresis, DNA fragments move from the negative electrode (cathode) to the positive electrode (anode).
- Heavier fragments move slower and therefore travel shorter distances, while lighter fragments move faster and travel further.

5. **Determining the Order from Cathode to Anode**:
- Since D is the heaviest, it will be closest to the cathode (starting point).
- Next, C will be further along the gel, followed by A, and finally B, which is the lightest and will be closest to the anode.

Thus, the order of the fragments from cathode to anode is:
- **D, C, A, B**

### Final Answer:
The correct option is (a) D, C, A, B.