Question

Bivalents are formed in meiosis during _________ phase.

• A. leptotene
• B. zygotene
• C. pachytene
• D. diakinesis

Answer 1

The correct option is (B):

Explanation of the correct option:

1. ​During zygotene stage of meiosis I, the homologous chromosomes undergo pairing and this is called as synapsis.
   
2. Synaptonemal complex is formed between the homologous chromosomes.
   
3. It is a ladder-like complex that hold the two homologous chromosomes together.
   
4. The pair of synapsed homologous chromosomes is called a bivalent or tetrad.

Explanation of the incorrect options:​

Option (A):

1. During leptotene stage, the chromatin which is a thread-like and loosely coiled structure starts to condense forming compact structures called chromosomes.​

Option (C):

1. Crossing over occurs during pachytene stage during which there is exchange of genes.
2. This is the stage in which variation in the genetic material occurs in the cell.

Option (D):

1. The homologous chromosomes separate during diakinesis and also the nuclelous and nuclear envelope disappear.
   

Final Answer: Bivalents are formed in meiosis during zygotene phase.