Answer:
The recombinant percentage C to D is 1% = 1cM (Option 1)
Explanation:
Two genes that are very close will have a few recombination events and are strongly bounded.
To calculate the recombination frequency, we have to know that 1% of recombinations = 1 map unit = 1 centiMorgan. And that the maximum recombination frequency is always 50%.
The map unit is the distance between the pair of genes for which every 100 meiotic products, one results in a recombinant one.
Available data:
- In a chromosome, there are 4 genes under study, A, B, C, and D
- Distance A-B = 15 cM
- Distance B-C = 9 cM
- Distance A-C = 6cM
- Distance A-D = 5 cM
The recombinant percentage between C and D equals their distances in centiMorgan. So we need to see the order of the genes on the chromosome.
- First, we need to identify the genes located in the extremes. These are the most distant from each other. A-B are 15 cM appart.
----A-----------------------------------------------------B---
║----------------------15 cM ---------------------║
- Now that we placed both genes, we can place the other genes. The second most distant are B-C = 9cM and then A-C = 6 cM
----A------------------C--------------------------------B---
║------6 cM-----║----------- 9 cM-----------║
- Finally, we can place D, which is 5 cM appart from A
----A-----------D-----C--------------------------------B---
║---5cM--║
Now that we can visualize better the location of genes on the chromosome, we can figure out the distance between D-C.
If the distance from A to C is 6 cM, and the distance from A to D is 5 cM, We just need to perform a subtraction, and we will get the distance from D to C.
(C-D) = (A-C) - (A-D) = 6 cM - 5 cM = 1 cM
----A-----------D-----C--------------------------------B---
║1cM║
