Hi, the question and answer to a genetics problem concerning map units betweeen

Question

Hi, the question and answer to a genetics problem concerning map units betweeen primary oocytes is below. Could somebody provide a more complete explanation of logic on how to solve a similar problem I will see on my test. I don't understand why the answer is 48 (correct) rather than 24 (incorrect). THANKS.

QUESTION

Assume that there are 12 map units between two loci in the mouse and that you are able to microscopically observe meiotic chromosomes in this organism. If you examined 200 primary oocytes, in how many would you expect to see a chiasma between the two loci mentioned above?

PARTIAL ANSWER:

48
Map units are the percentage of recombination. So for every 100 meiosis occurances, 12 times crossover should occur. Based on that, 12% of 200 is 24. But because percent is per every 100, you would multiply 24*2 and get 48.

Explanation / Answer

For every 100 meiosis occurrences, 12 times crossover should occur and the number doubles because meiosis occurs in two stages, meiosis I and meiosis II.

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