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Multiple Choice
During meiosis, crossing over (genetic recombination) between non-sister chromatids most commonly occurs during which phase?
A
Prophase I (specifically during pachytene of prophase I)
B
Prophase II
C
Anaphase I
D
Metaphase I
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1
Recall the stages of meiosis, which include Prophase I, Metaphase I, Anaphase I, Telophase I, followed by Prophase II, Metaphase II, Anaphase II, and Telophase II.
Understand that crossing over, or genetic recombination, involves the exchange of genetic material between homologous chromosomes, specifically between non-sister chromatids.
Identify that crossing over requires homologous chromosomes to pair up closely, a process called synapsis, which occurs during Prophase I of meiosis.
Recognize that within Prophase I, crossing over most commonly happens during the pachytene substage, when the synaptonemal complex is fully formed and chromatids are tightly paired.
Conclude that crossing over does not occur during Prophase II, Anaphase I, or Metaphase I because these stages either lack homolog pairing or the physical conditions necessary for recombination.