If map distance between genes P and Q is 4 units, between P and R is 11 units, and between Q and R is 7 units, the order of genes on the linkage map can be traced as follows

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Answer

To solve the problem of determining the order of genes P, Q, and R based on their map distances, we can follow these steps:

### Step 1: Identify the given distances
We have the following distances:
- Distance between P and Q = 4 units
- Distance between P and R = 11 units
- Distance between Q and R = 7 units

### Step 2: Analyze the distances
From the distances provided, we can see:
- The smallest distance is between P and Q (4 units).
- The largest distance is between P and R (11 units).
- The distance between Q and R (7 units) is greater than P and Q but less than P and R.

### Step 3: Determine the gene order
Since P and R are the furthest apart (11 units), we can place them at the ends of our linkage map.
- Let's place P on the left and R on the right because they are the furthest apart.
- Now, since Q is only 4 units away from P, we can place Q between P and R.

This gives us the order: **P - Q - R**.

### Step 4: Verify the distances
- The distance between P and Q is indeed 4 units.
- The distance between Q and R can be calculated as follows:
- Distance P to R = Distance P to Q + Distance Q to R
- 11 units = 4 units + Distance Q to R
- Therefore, Distance Q to R = 11 units - 4 units = 7 units, which matches the given distance.

### Conclusion
The order of the genes on the linkage map is **P - Q - R**.