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A single crossover event exchanges equivalent DNA between:
ATwo separate daughter cells
BTwo sister chromatids
CTwo non-sister chromatids
DTwo unrelated chromosomes
Answer & Solution
Correct answer: C. Two non-sister chromatids
1. Crossing over happens while the homologues are paired in synapsis.
2. It swaps matching stretches between the maternal and the paternal copy.
3. A single crossover event between homologous non-sister chromatids leads to a reciprocal exchange of equivalent DNA between a maternal chromosome and a paternal chromosome.
4. Sister chromatids are near-identical copies, so exchanging between them would change nothing.
_Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 11 'Meiosis and Sexual Reproduction', sections 11.1-11.2_
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