Question

Synapsis occurs in what stage of Prophase I of meiosis I?
A) Lepottene
B) Zygotene
C) Diplotene
D) Pachytene

Answer 1

The process by which one cell divides into four daughter cells is known as meiosis. It is a reproductive process in which the genetic material is half of the original amount. Meiosis is divided into two phases- Meiosis I and Meiosis II.

Complete answer:
Prophase I is the first phase of Meiosis I. it is the longest and the most complex phase of Meiosis. It is further divided into five phases. They are as follows:
Leptotene- This phase includes the compaction of chromosomes as they become visible under the light microscope.
Zygotene- Zygotene involves the process of synapsis. It is defined as the pairing of homologous chromosomes due to the formation of the synaptonemal complex between the two chromosomes. This stage is short-lived and the homologous pair of chromosomes formed is called bivalent or a tetrad.
Pachytene- Pachytene involves the appearance of recombination nodules which are the sites at which crossing over takes place between sister chromatids of homologous chromosomes. Crossing over is an enzyme-mediated process that leads to the recombination of genetic material on two chromosomes. The enzyme is recombinase.
Diplotene- this stage involves the dissolution of the synaptonemal complex. Dissolution increases the tendency of the recombined homologous chromosomes of the bivalents to separate from each other except at the site of crossover. They form an ‘X’ shaped structure known as chiasmata.
Diakinesis- this stage involves the terminalisation of chiasmata. In this stage, chromosomes are fully condensed and a mitotic spindle is assembled to prepare the homologous chromosomes for separation.

Hence, the correct answer is option B.

Note:
The next phase after Prophase I is Metaphase I. the bivalent chromosomes align on the equatorial plate and microtubules from the opposite poles of the spindle attach to the chromosomes. In Anaphase I, homologous chromosomes separate, and chromatids remain attached at the centromere. In Telophase I, the nuclear membrane and nucleolus reappear. Meiosis II is similar to mitosis.