Problem 39 - Objective Biology for NEET

Question

The beginning of diplotene is characterized by (a) Recombination (b) Synapsis (c) Dissolution of synaptonemal complex (d) Formation of tetrad

Step-by-Step Solution

Answer

The beginning of diplotene is characterized by the dissolution of the synaptonemal complex. Therefore, the correct choice is option (c).

Step 1: Understanding what the diplotene stage of meiosis involves

The diplotene stage is part of Prophase I of meiosis. During this stage, the synaptonemal complex - a protein structure that forms between two homologous chromosomes during meiosis - begins to break down and homologous chromosomes start to pull apart, although they remain connected at certain points called chiasmata. These chiasmata are where recombination, also known as crossing over, has occurred.

Step 2: Identifying the correct option from the given alternatives

With the knowledge from step 1, you can see that at the start of the diplotene stage, the dissolution of the synaptonemal complex is occurring, as the chromosomes begin to separate from each other. This means that option (c) is the correct answer.

Key Concepts

Diplotene Stage

In the complex process of meiosis, cells undergo several stages to ensure the proper segregation of chromosomes. The diplotene stage is one of these critical phases in Prophase I. It is characterized by the beginning of the separation of homologous chromosomes. As these chromosomes start to move apart, they reveal the chiasmata—sites where genetic material has been exchanged during recombination. Although the chromosomes are partially separating, they remain connected at these chiasmata, which are key to ensuring genetic diversity. This stage is crucial because it marks the dissolution of the synaptonemal complex, setting the stage for the next phase of meiosis.

Synaptonemal Complex

The synaptonemal complex plays a vital role during meiosis. It is a protein structure that forms between homologous chromosomes, allowing them to pair up tightly. This pairing is essential for the accurate exchange of genetic material. The synaptonemal complex ensures that crossing over occurs between the aligned chromosomes, facilitating genetic diversity in the resultant gametes. As meiosis progresses into the diplotene stage, the synaptonemal complex begins to break down. This breakdown is a signal that chromosomes are ready to start disassociating, even as they remain tethered at chiasmata.

Recombination

Recombination, also referred to as crossing over, is a process that increases genetic variation. It occurs during Prophase I of meiosis when homologous chromosomes are aligned closely together. The synaptonemal complex facilitates this proximity, enabling segments of DNA to be exchanged between non-sister chromatids. This exchange produces new combinations of alleles, leading to genetic diversity in offspring. This step is significant because it contributes to the unique genetic makeup of each individual. The visible outcome of recombination can be seen in the form of chiasmata during the diplotene stage of meiosis.

Chiasmata

Chiasmata are the physical manifestations of crossing over between homologous chromosomes during meiosis. They are crucial for ensuring that recombination has taken place. These structures appear as X-shaped configurations where chromosomes overlap and exchange genetic material. During the diplotene stage of Prophase I, as the synaptonemal complex dissolves, chiasmata become clearly visible. They effectively hold the homologous chromosomes together, preventing them from drifting apart too soon and ensuring a successful meiotic division. The role of chiasmata is vital, as they maintain genetic linkage and contribute to accurate chromosomal alignment and segregation.