The correct answer is Option D: Pachytene. Here's why:

Meiosis is a cell division process that produces gametes (sperm and egg cells) with half the number of chromosomes as the parent cell. During meiosis, homologous chromosomes (pairs of chromosomes with the same genes) undergo a process called crossing over, which involves the exchange of genetic material.

Let's break down the stages of prophase I of meiosis, where recombination occurs:

• Leptotene: Chromosomes condense and become visible.
• Zygotene: Homologous chromosomes begin to pair up, forming structures called synaptonemal complexes.
• Pachytene: This is where crossing over actually takes place. The synaptonemal complexes are fully formed, and the chromosomes are tightly paired. The exchange of genetic material between non-sister chromatids occurs within these complexes.
• Diplotene: The synaptonemal complexes begin to dissolve, and the chromosomes start to separate. However, they remain attached at points called chiasmata, which are the visible sites of crossing over. Recombination is complete at this stage.
• Diakinesis: The chromosomes condense further, and the chiasmata become more prominent. The nuclear envelope breaks down, and the spindle fibers start to form.

Therefore, recombination is completed by the end of Pachytene, where the exchange of genetic material is finished. Although chiasmata are still visible in Diplotene, the actual recombination event is already completed in Pachytene.