Question

In which stage does the crossing over occur ?

Answer 1

Crossing over:

1. Crossing over occurs during the prophase I stage. It is the most important stage of first meiotic division and differs considerably from the prophase of mitosis.
2. It is divided into six stages such as Pre-leptotene, Leptotene, Zygotene, Pachytene, Diplotene and Diakinesis.
3. Pachytene or Pachynema is the longest stage in mammalian spermatogenesis. Homologous chromosomes come close together to form a pair called bivalent. This pairing of chromosomes is known as synapsis. The pairing is followed by crossing over.
4. Crossing over is exchange of chromatid segments between the two chromosomes of homologous pair. So the crossing over occur during Prophase I.