Diplotene

The distinct separation of chromatids from homologous chromosomes marks diplotene, the 4th subphase of prophase I of the meiotic cell division. The locations on the chromosomes at which a recombination took place are known as chiasms, and you can see them during this subphase.

When a strand of genetic material is severed to connect to another molecule with distinct genetic material, recombination takes place. Acetylene, a state of stop or latency observed by the eggs during diplotene, is a possible outcome of meiosis.

Meiosis

Meiosis is a specific type of cell division that results in the production of four haploid cells by cutting the number of chromosomes in half.

Each haploid cell, which develops from sex cells also known as gametes, differs genetically from the stem cell from whence it was derived.

All sexually reproducing unicellular (eukaryotic) & multicellular organisms, including plant cells, animals, as well as fungus, go through this process. Aneuploidy is a symptom of meiosis mistakes, which are the most common genetic source of impairments and the main cause of miscarriages.

Phases of Meiosis

In the cell division process known as meiosis, the number of chromosomes is cut in half. Two cycles of nuclear & cellular division are known as meiosis I & meiosis II. One of the stages in meiosis I process is prophase I.

Diplotene is prophase 1’s fourth stage. The pachytene stage crosses over after the diplotene stage.

Leptotene

Chromosome condensation takes place in this initial stage. Under a light microscope, chromosomes can be seen. They resemble nucleosomes, a chain of beads. Each chromatid is currently quite near to the other at this stage. This stage, which happens during the leptotene-zygotene transition, is incredibly brief.

Zygotene

Chromosome pairing begins at this stage, and this connection process, known as synapsis, results in the development of the intricate structure called synaptonemal complex. In the meiotic process known as synapsis, homologous chromosomes couple up and remain attached to one another in order to exchange genetic material. It’s called a tetrad or bivalent when two homologous chromosomes pair together.

Pachytene

Once a tetrad has formed, the procedure of crossing over and subsequent recombination will begin, where a small amount of genetic material from the parental DNA sequences is switched over to increase gene variety. The chromatid sisters start to separate from one another at this point, while the chromosomes continue to be joined as a pair. This makes them much more distinct when viewed under an electron microscope. The chiasma connects two chromatids that are not sisters.

Diplotene

Pachytene precedes the substage known as diplotene, sometimes known as diplonema. Prior to diplotene, homologous chromosomes have formed tetrads or bivalents (which have the genetic value of both the parents), thicken, shorten, and separate sister chromatids.

At the diplotene stage, a zipper-like structure known as the synaptonemal complex forms between the chromosomes which have paired and then degrades, enabling the homologous chromosomes to slightly split.

As the chromosomes unroll, DNA transcription is possible. However, in the chiasms, the places where the crossing took place, the homologous chromosomes from each formed pair continue to be securely connected. The chiasms stay attached to the chromosomes until the anaphase I transition, when they split.

Diplotene causes the synaptonemal complexes to separate, the centre space to grow, and the components to vanish, leaving only the chiasm-regions behind. The lateral components are also retained, and they work well and independently of one another.

Diakinesis

Diplotene is followed by diakinesis, during which chiasmata are terminalised. This phase serves as the entry point into the metaphase. In order to get ready for the following stage of meiosis I, more systemic alterations are taking place at this point. The nuclear envelope and nucleolus both dissolve. The centrioles that help produce spindles are free to move as a result.

The primary components of spindle construction are microtubules found in the cytoplasm of the cell.

Diplotene Stage

The matching homologues begin to shift independently after pachytene; this phase is known as diplotene. The synaptonemal multipart disintegrates, but each bivalent’s two homologous chromosomes are still connected by one or more chiasmata, which represent the points at which crossing over has occurred.

These are the modifications that this sub-phase brings about:

1. The bivalents’ chromosomes begin to repel one another. Chromosomes begin to drift apart as a consequence.

2. However, the chromosomes continue to be joined together thanks to a ‘X’-shaped chiasma that forms at one or more locations between non-sister chromatids.

3. The chiasma is first broken down, and the fragmented chromatids are then put back together differently or inversely from one another.

4. Crossing-over is the term used to describe this kind of exchange between the homologous chromosomes.

5. Terminalization is the word for the movement of the chiasma towards the pole as a result of an increase in the repulsion between two homologous chromosomes.

The chiasmata gradually move towards the telomeres and become fewer in number as a result of the forces that reject the homologous chromosomes; this is a process known as chiasma terminalization. The precise location and quantity of crossovers are therefore unknown during later phases of diplotene.

Importance of Diplotene 

1. Oocytes are roughly synchronised in the diplotene stage of prophase I around the 8th month of embryonic development.

2. From birth till puberty, when ovarian follicles start to mature one at a time and the oocyte restarts the last phase of diplotene, the cells will stay in this subphase.

3. Human oocytes stop maturing at the diplotene stage, prior to birth, during the process of oogenesis (formation of the ovules). When a child reaches puberty, the process is restarted; this pause in meiotic division is referred to as dictyate or dictyotene.

4. The oocyte is in the first or second meiotic division when ovulation starts. Until fertilisation, when the anaphase of 2nd division takes place and the female pronucleus is prepared to fuse with the male, the second division is put on hold.

Conclusion

Meiosis is the process by which the parent cell divides into four haploid daughter cells, each of which has half as much genetic material as the original cell. Meiosis results in gametes.

There are 5 phases of prophase I of meiosis which are as follows:

1. Leptotene

2. Zygotene

3. Pachytene

4. Diplotene

5. Diakinesis

The paired chromosomes begin to divide into 2 pairs of chromatids in Diplotene. The dissolution of synaptonemal complex ends the synapsis. At the Chiasma, the homologous pairs of the chromosomes are still connected. The chromosomes start to coil, which magnifies the Chiasma under a microscope.