There are three genes a, b, c, percentage of crossing over between a and b is 20%, b and c is 28% and a and c is 8%. What is the sequence of genes on chromosome?

Options

A. b, a, c
B. a, b, c
C. a, c, b
D. None of these

Explanation

To determine the sequence of genes A, B, and C on a chromosome based on the given percentages of crossing over, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Given Information**:
- The percentage of crossing over (recombination frequency) between:
- A and B = 20%
- B and C = 28%
- A and C = 8%

2. **Interpret the Recombination Frequencies**:
- The recombination frequency is directly proportional to the distance between genes on a chromosome. This means that a higher percentage indicates that the genes are further apart, while a lower percentage indicates that they are closer together.

3. **Analyze the Percentages**:
- A and C have the lowest recombination frequency (8%), indicating that they are the closest genes on the chromosome.
- A and B have a recombination frequency of 20%, indicating they are further apart than A and C but closer than B and C.
- B and C have the highest recombination frequency (28%), indicating they are the furthest apart.

4. **Determine the Gene Order**:
- Since A and C are closest (8%), they must be adjacent to each other.
- B must be placed between A and C because the distance between B and C (28%) is greater than the distance between A and C (8%).
- Therefore, the order of the genes on the chromosome is B, A, C.

5. **Final Sequence**:
- The sequence of the genes on the chromosome is: **B - A - C**.