Genetics Question from Next Step FL#1

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Jan 14, 2013
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What aspects separate single-crossover events from double-crossover events?

A)Single-crossover events result in one-way displacement of chromosomal content from one chromosome to another, while double-crossover events reverse this one-way displacement resulting in chromosomes identical to the pre-crossover chromosomes.

B)Single-crossover events occur during mitosis when a cell splits into two cells, while double-crossover events occur during meiosis when a cell splits into four cells.

C)Single-crossover events affect only the ends of chromosome arms, while double-crossover events affect segments in the middle of chromosome arms.

D)Single-crossover events affect one arm of each chromosome, while double-crossover events affect two arms of each chromosome.

Answer Explanation:

C is correct. A double-crossover event is one in which chromosomal arms of homologous chromosomes cross over in two different places along the arm. This results in a section in the middle of each chromosome being exchanged.

A: A double-crossover event occurs in two different places along the chromosome arm, resulting in a segment exchange, not a reversal of the original crossover.

B: Crossover events only occur during meiosis, not during mitosis.

D: Both single- and double-crossover events will only affect one arm of each chromosome.

I am a little confuse as to why A could not be the correct answer. If someone could help that would be appreciated.



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Jun 26, 2014
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The reason A is not correct is because a double crossover will not restore the original chromosome (result "in chromosomes identical to the pre-crossover chromosomes").