The phase of meiosis during which the non-sister chromatids of homologous chromosomes may exchange their segments:
Correct answer: B. Pachytene
- A. Leptotene
- B. Pachytene
- C. Diplotene
- D. Zygotene
Explanation
Leptotene is the first stage of the prophase of meiosis, during which each chromosome becomes visible as two fine threads. Pachytene is the third stage of the prophase of meiosis, following zygotene, during which the paired chromosomes shorten and thicken, the two chromatids of each separate, and exchange of segments between chromatids may occur. Diplotene is the fourth stage of the prophase of meiosis, following pachytene, during which the paired chromosomes begin to separate into two pairs of chromatids. Zygotene is the second stage of the prophase of meiosis, following leptotene, during which homologous chromosomes begin to pair. The correct answer is, therefore, B.
This question appeared on the HEC Phase II 2017 paper, which you can sit online with every answer explained.
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About Gene Linkage and Crossing Over
Linked genes lie on the same chromosome and tend to pass together, unlike genes that assort independently on different chromosomes. The topic connects linkage with homologous pairing, crossing over during prophase I of meiosis, recombinant and parental offspring, and recombination frequency as an estimate of gene distance.
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