Botany - Cell Cycle and Cell Division Question with Solution | TestHub

Zygotene: 

• Chromosomes start pairing together. This process is called synapsis. The paired chromosomes are called homologous chromosomes. 
• The formation of synapsis is accompanied by the formation of the synaptonemal complex. 
• The synaptonemal complex by a pair of homologous chromosomes is called a bivalent or a tetrad.

Pachytene: 

• Bivalent chromosomes clearly appear as tetrads, at this stage. 
• Recombination nodules appear. These nodules are the sites at which crossing overtakes place between non-sister chromatids of the homologous chromosomes. 
• The exchange of genetic materials between two homologous chromosomes takes place during crossing over. This leads to the recombination of genetic materials on the two chromosomes.

Diakinesis: 

• Chiasmata is terminated at this stage. 
• Meiotic spindles are formed to prepare the homologous chromosomes for separation. 
• The nucleolus disappears and the nuclear envelope breaks down by the end of diakinesis.

Metaphase I: 

• The bivalent chromosomes are aligned on the equatorial plate. 
• Spindle fibres from opposite poles attach to the pair of homologous chromosomes.