Four genes A, B, C and D located on chromosome and cross over frequencies between different genes are :
A – D `implies` 20%, A – C `implies` 4%
C – D `implies` 16%, B – C = 9%
A – B = 5%
based on above data, what is the arrangement of linked gene on chromosome

Options

A. A – B – C – D
B. B– A – C – D
C. C B A D
D. C A B D

Answer

To determine the arrangement of the linked genes A, B, C, and D on a chromosome based on the provided crossover frequencies, we can follow these steps:

### Step 1: Analyze the Crossover Frequencies
We have the following crossover frequencies:
- A – D: 20%
- A – C: 4%
- C – D: 16%
- B – C: 9%
- A – B: 5%

### Step 2: Establish the Position of Genes
We start by placing gene A on the chromosome. Since A – C has the smallest crossover frequency (4%), we can place C very close to A.

### Step 3: Position C Relative to A
Since A – C is 4%, we can represent this as:
- A ---- 4% ---- C

### Step 4: Position D Relative to C
Next, we know that C – D is 16%. Since A – D is 20%, we can deduce that D is positioned 16% from C, which means:
- A ---- 4% ---- C ---- 16% ---- D

This gives us a total distance from A to D of 20%, which is consistent with the given data.

### Step 5: Position B Relative to A and C
Now we need to place gene B. We know:
- A – B = 5%
- B – C = 9%

If we place B to the left of A, we would have:
- B ---- 5% ---- A ---- 4% ---- C ---- 16% ---- D

This arrangement would make B – C = 9%, which is correct.

### Step 6: Confirm the Arrangement
Now we can confirm the arrangement:
- B is 5% from A.
- A is 4% from C.
- C is 16% from D.
- B is 9% from C.

Thus, the final arrangement of the genes on the chromosome is:
**B - A - C - D**

### Conclusion
The correct arrangement of the linked genes on the chromosome is B, A, C, D.

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