MCAT Biology Question 166: Answer and Explanation

Home > MCAT Test > MCAT biology practice tests

Test Information

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:

Previous       Next