Question

If there are $30$ chromosomes in $G_1$ in phase, then what will be number of bivalents in zygotene stage?

• A. 30
• B. 15
• C. 45
• D. 60

Answer 1

The correct option is B 15

Though the 30 chromosomes from G phase will replicate during S-phase, they will be attached at the centromeric site by cohesin molecules and hence the number of chromosomes will remain 30.

When the zygotene stage begins, the homologous chromosomes pair up to form bivalents. Hence, the 30 chromosomes will form 15 bivalents/tetrads in the zygotene stage of prophase.

So the correct answer is'15'.