# Thread: Molecular Biology - Genetics: Recombination frequency question from mock exam

1. ## Molecular Biology - Genetics: Recombination frequency question from mock exam

Hi,

I have a bachelor in pharmaceutical chemistry but I am doing subject GRE in Biochemistry, molecular and cellular biology. The following question is from the mock exam.

"In a series of two-factor crosses, 30 percent recombination occurs between gene A and gene B, and 26 percent recombination between gene B and gene C. If the order of genes on the chromosome is A-B-C, how much recombination will be seen between A and C in a two-factor cross?
A 4%
B 8%
C 28%
D 50%
E 56%
"
I looked up the concept of recombination frequency and by my current understanding of this concept the answer should be E. However, the real answer is D.
Please, someone explain how you get 50% distance between A and C.

Thanks  Reply With Quote

2. ## Re: Molecular Biology - Genetics: Recombination frequency question from mock exam Originally Posted by kuzminpe Hi,

I have a bachelor in pharmaceutical chemistry but I am doing subject GRE in Biochemistry, molecular and cellular biology. The following question is from the mock exam.

"In a series of two-factor crosses, 30 percent recombination occurs between gene A and gene B, and 26 percent recombination between gene B and gene C. If the order of genes on the chromosome is A-B-C, how much recombination will be seen between A and C in a two-factor cross?
A 4%
B 8%
C 28%
D 50%
E 56%
"
I looked up the concept of recombination frequency and by my current understanding of this concept the answer should be E. However, the real answer is D.
Please, someone explain how you get 50% distance between A and C.

Thanks
If there is 30cM between A and B, and 26cM between B and C, you can not add up those numbers and say A and C are 56cM apart as 56>50cM. The reason is, the maximum recombination between two genes is 50%.
So you have to consider that A and C are far apart and that puts their recombination rate at 50%.  Reply With Quote