Question

Dissolution of synaptonemal complex occurs during
A) Zygotene
B) Diplotene
C) Leptotene
D) Pachytene

Answer 1

Meiosis is a division which occurs in a diploid cell and gives rise to four haploid cells or n nuclei, each having half the number of chromosomes as compared to the parent cell. Two divisions of meiosis are – meiosis I and meiosis II. In meiosis I the chromosomes become genetically different due to crossing over and their number is reduced to half. It is also called heterotypic or reduction division.

Complete answer:
Synaptonemal complex is a ribonucleoprotein that is one part is of ribonucleic acid and other part is protein that’s why it is called as complex. The main function of this is that it helps in the synapsis. When the pairing of homologous chromosomes occurs in which one structure is needed for binding the two chromosomes together that structure is called a synaptonemal complex. It stabilizes the paired condition of chromosomes till crossing over is completed.

Let us analyze the given options:
A) Zygotene – In this stage the pairing of homologous chromosomes occurs and it produces a complex, known as synaptonemal complex. During synapsis, the pair or bivalent form of chromosomes formed.
B) Diplotene – In this stage the dissolution of synaptonemal complex or nucleoprotein fusion complex occurs. The points of attachment after the partial dissolution are called chiasmata and this chiasmata mark the sites of crossing over.
C) Leptotene – It is the first stage of prophase I, in this stage the condensation of chromosomes occurs.
D) Pachytene – In this stage the crossing over takes place.

So, the correct answer is option (B) Diplotene.

Note: Significance of meiosis-I:
- It separates the homologous chromosomes to reduce the chromosome number to haploid stage. It is essential for sexual reproduction.
- It may at times cause chromosomal mutation by abnormal disjunction.
- It introduces variation by forming new combinations of genes.