Question

Recombination between homologous chromosomes is completed by the end of

• A. Diakinesis
• B. Zygotene
• C. Diplotene
• D. Pachytene

Answer 1

The Correct Option is D

The question asks about the stage at which recombination between homologous chromosomes is completed during meiosis. To answer this, we must understand the stages of prophase I in meiosis, where homologous recombination occurs. Prophase I is divided into five sub-stages: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.

1. Leptotene: Chromosomes begin to condense and become visible.
2. Zygotene: Synapsis begins; paired homologous chromosomes start aligning but recombination is not yet complete.
3. Pachytene: This is the stage where synapsis is complete, and homologous recombination, or crossing over, is completed. It is characterized by the formation of the synaptonemal complex, where genetic material is exchanged between homologous chromosomes.
4. Diplotene: The synaptonemal complex disassembles, and homologous chromosomes start to separate, but remain connected at chiasmata where crossing over occurred.
5. Diakinesis: Further chromosome condensation occurs, and the homologous chromosomes are prepared for segregation.

Thus, the correct answer is Pachytene, as recombination between homologous chromosomes is completed by the end of this stage.

The other options are not correct because:

• Diakinesis: At this stage, chromosomes are condensing and preparing for segregation; recombination has already been completed.
• Zygotene: Synapsis begins but recombination is not yet complete.
• Diplotene: Chromosomes start separating and recombination sites (chiasmata) are evident, but the actual recombination has already been completed in Pachytene.

Therefore, the answer is justified as Pachytene.