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Multiple Choice
During meiosis, in which stage does crossing over (homologous recombination) occur?
A
Prophase II
B
Metaphase I
C
Anaphase I
D
Prophase I (specifically during pachytene)
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1
Recall the stages of meiosis: Meiosis I includes Prophase I, Metaphase I, Anaphase I, and Telophase I; Meiosis II includes Prophase II, Metaphase II, Anaphase II, and Telophase II.
Understand that crossing over, or homologous recombination, is the process where homologous chromosomes exchange genetic material to increase genetic diversity.
Identify that crossing over occurs during Prophase I of meiosis, specifically in the pachytene substage, when homologous chromosomes are tightly paired (synapsed).
Note that during Metaphase I, homologous chromosomes align at the metaphase plate, but crossing over has already occurred by this point.
Recognize that Prophase II and Anaphase I do not involve crossing over; Prophase II involves preparation for the second meiotic division, and Anaphase I involves separation of homologous chromosomes.