Question

Identify the substage of Prophase I of meiosis during which synapsis takes place.
A. Leptotene
B. Pachytene
C. Diplotene
D. Zygotene

Answer 1

Hint: The process by which two homologous chromosomes pair is known as synapsis. Homologous chromosomes are those which pair up during sexual reproduction and occur within the cell. And also forms an RNA-protein complex known as the synaptonemal complex.

Complete answer: Synapsis is an event that takes place in the zygotene stage of prophase I of meiosis. The synaptonemal complex is responsible for keeping the homologous chromosomes together. The chromosome arrangement thus formed is known as a tetrad, since each of the chromatids in the two chromosomes are very different from each other.
Considering the other given options:
-Leptotene is marked as the first stage of prophase-I of meiosis. In this stage, the diffused chromatins form longer and thinner strands. Hence, the chromosomes are converted into a fine thread like structures.
-Pachytene is the third stage involved in prophase-I of meiosis. This stage is characterized by a fully formed synaptonemal complex. The chromosomes thicken in this phase and recombination occurs now. Crossing over is done through the process of recombination.
-Diplotene is the fourth stage of prophase-I, the major events happening in the stage is the loosening of the synaptonemal complex, and the sister chromatids from the homologous chromosomes loosen from each other.
Thus, the most appropriate answer was found to be D, i.e., Zygotene is the stage of Prophase-I at which synapsis takes place.

Note: The end product of meiosis-I are four daughter cells, which are haploid in nature. This process is present in cells undergoing reduction division such as the gametes. The order wise steps happening in prophase-I of meiosis-I are leptotene, zygotene, pachytene, diplotene, and diakinesis.