1. At the zygotene stage, attraction between homologous chromosomes begins. Homologous chromosome pairs come close to each other and pair up.
2. The process of pairing of chromosomes is called synapsis and a pair of chromosomes is called bivalent.
3. A structural change occurs as two chromosomes join in bivalents.
4. At a later stage, the bivalent chromosomes divide to form chromatids.
5. Crossing over occurs between non-sister chromatids. Zygotes are required for crossover to occur.
6. Crossing over results in biodiversity. The role of zygotes in creating biodiversity in the living world is undeniable.