Question

In the diplotene stage,

• A. Chromosomes are thin and long.
• B. Homologous chromosomes of bivalent starts moving apart.
• C. Bivalents become very short and chaismata move towards ends of chromosomes.
• D. Chromosomes have reached poles.

Answer 1

The correct option is B Homologous chromosomes of bivalent starts moving apart.

After the pairing of homologous chromosomes and formation of a bivalent structure in the zygotene stage, crossing over occurs between non-sister chromatids of homologous chromosomes in the pachytene stage. Then comes the diplotene stage.

The beginning of diplotene stage is marked by the dissolution of the synaptonemal complex and chiasma formation. The chiasma formation is the indication of completion of crossing over and beginning of the separation of chromosomes (disjunction). This stage marks the beginning of chiasma terminalisation. The chiasma is the result of the fact that chromosomal parts begin to repel each other except in the region where these are in contact. It is a X-shaped structure.

Hence, in diplotene stage, homologous chromosomes of bivalent start moving apart and this results in the formation of chiasma. So, the correct answer is 'Homologous chromosomes of bivalent starts moving apart'.