If gene frequency between genes a and c is 2%; b and c is 13%; b and d 4%; a and b 15%; c and d 17 and a and d 19%. The sequence of genes in a chromosome is

The correct option is a,c,b,d.

Step-by-step Explanation:

In genetic mapping, the recombination frequency (or gene frequency) between genes is directly proportional to the physical distance between them on a chromosome. A 1% recombination frequency is equivalent to 1 map unit or centimorgan (cM). Therefore, we can translate the given percentages into relative distances as follows:
- Distance between a and c = 2 cM
- Distance between b and c = 13 cM
- Distance between b and d = 4 cM
- Distance between a and b = 15 cM
- Distance between c and d = 17 cM
- Distance between a and d = 19 cM

Step 1: Identify the genes at the outer ends of the map
The largest distance is between genes a and d, which is 19 cM. This indicates that a and d are the endpoint genes located at the opposite ends of this chromosome segment.

Step 2: Position the internal genes relative to the endpoints
First, let's locate gene b. We know that:
- Distance(a, b) = 15 cM
- Distance(b, d) = 4 cM

Since the sum of these distances equals the total distance between the endpoints:

$15+4=19$
Gene b must lie between a and d, closer to gene d.

Next, let's locate gene c. We know that:
- Distance(a, c) = 2 cM
- Distance(c, d) = 17 cM

Since the sum of these distances also equals the total distance between the endpoints:

$2+17=19$
Gene c must also lie between a and d, but very close to gene a.

Step 3: Verify the remaining distances
With the proposed sequence being a - c - b - d, let's check if the distance between c and b is consistent with our values:

$\text{Distance(c, b)}=\text{Distance(a, b)}-\text{Distance(a, c)}$

$\text{Distance(c, b)}=15-2=13\text{cM}$
This perfectly matches the given recombination frequency of 13% between genes b and c.

Thus, the sequence of the genes on the chromosome is a,c,b,d.