MCAT Biology Question 166: Answer and Explanation
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Question: 166
1. What is the gene order of linked genes M, N, O, and P, given the following recombination frequencies?
MN: 6% NO: 18%
MO: 12% NP: 1%
MP: 5% OP: 17%
- A. MOPN
- B. NPMO
- C. ONPM
- D. PNMO
Correct Answer: B
Explanation:
This is a gene-mapping problem. Because there is a correlation between the frequency of recombination and the distance between genes on a chromosome, if we are given the frequencies, we can determine gene order. Remember that one map unit equals 1 percent recombination frequency. The easiest way to begin is to determine the two genes that are farthest apart; in this case, N and O recombine with a frequency of 18%, so they are 18 map units apart on the chromosome:
N and P recombine with 1% frequency, and P and O recombine with 17% frequency, so P must be between N and O:
Finally, M and P recombine with 5% frequency, and M and O recombine with 12% frequency, so M must be between P and O: