Question

Which one of the following list contains the correct order of meiosis?

• A. Separation of sister chromatids, recombination, formation of the synaptonemal complex, separation of homologous chromosomes
• B. Separation of homologous chromosomes, formation of the synaptonemal complex, recombination, separation of sister chromatids
• C. Formation of synaptonemal complex, recombination, separation of sister chromatids, separation of homologous chromosomes
• D. Formation of the synaptonemal complex, recombination, separation of homologous chromosomes, separation of sister chromatids

Answer 1

The correct option is D Formation of the synaptonemal complex, recombination, separation of homologous chromosomes, separation of sister chromatids

The various events of meiosis given in the question occur in the following sequence:

• Propahse I- It is the longest phase of meiosis. Three major event occur in propahse I, that are- condensation of chromatin into chromosome, next is formation of synapsis, and finally crossing over. These events occurs in 5 substeps:

A) Leptonema- A cell destined to become a gamete enters this stage. In this step chromatin condensation takes place to form a chromosome structure.
B) Zygonema- In this stage, the homologous pairs of chromosomes to form a synapse. The pairing or coming together of homologous chromosomes is called synapsis. This is also known as synaptonmal complex. The pairing may start at any part of the chromosomes, e.g., near the end or near the centromere. The pairing is also highly specific, i.e., homologous chromosomes that come in pairs must be of equal length and have the same centromere position. The paired chromosomes are called bivalent or tetrad chromosomes.
C) Pachytene- In this stages, there is the chaismata formation takes place where crossing over occurs. During the crossing over there is actual physical exchange of the segment of the chromosomes takes place. This is known as recombination.
D) Diplotene- Once the crossing over is accomplished the chromosome pairs begins to separate. The chromosomes uncoil slightly to allow DNA transcription.
E) Diakinesis- This is an final stage of propahse I, here the chromosomes. The homologous chromosomes separate further but are still attached by chiasmata, which moves towards the ends of the chromatids in a process referred to as terminalization. The nuclear envelope and nucleoli disintegrates, and the meiotic spindle begins to form.

Hence, correct order of mitotic events which occur during meiosis is: Formation of synaptonemal complex, recombination, separation of homologous chromosomes, separation of sister chromatids.