Prometaphase

In the cell division theory, we have two types of cell division namely mitosis and meiosis. In meiosis, the haploid cells are formed in many phases. In those phases, we have a stage called prometaphase in eukaryotic cell division. Prometaphase happens in both meiosis 1 and meiosis 2.  We will discuss what happens in prometaphase 2 in detail.

Prometaphase

Meiosis I

In meiosis 1, two haploid cells are formed from one diploid cell. Haploid cells have a single set of unpaired chromosomes, whereas the diploid cell has one pair of chromosomes. In meiosis 1, we have many phases, including prophase 1, prometaphase 1, metaphase 1, anaphase 1, and telophase 1.

The chromosomes get condensed and the microtubules get attached to the metaphase plate. Then, the centromere breakdown happens and chromosomes move to the opposite poles, resulting in two gamete cells by cytokinesis. The gamete cell is a cell formed during this phase, which has only half the number of chromosomes. Meiosis 1 is also called reductive division.

Prometaphase 1 in meiosis

The phase between the metaphase and prophase is called prometaphase in cell division theory. The centrosome in prophase divides and moves to the opposite side of the cell and has a condensed chromosome. 

Steps involved in prometaphase

The nuclear envelope and microtubules of the cell break down. The nuclear membrane is made up of two lipid layers. In those layers, we have pores that allow the passage of ribosomes through the membrane.

And the nuclear membrane also gets broken and releases the molecules. During telophase, these broken membranes merge to form two new cells.

The microtubules get attached to the chromosome tetrads. This happens with the help of kinetochores, so-called kinetochore microtubules. The kinetochores are the special area in the centromere. Also, we have another type of microtubule called a polar microtubule. This microtubule helps in pushing centrosomes apart from each other. The sister chromatids in the chromosomes get attached to each other with the help of proteins present in the centrosome. 

The spindle apparatus is a matrix in the cell. It contains many types of microtubules that move along with motor proteins. There would be changes in the overall length of the microtubule. Then the phase moves to the next phase, anaphase.

In meiosis, prometaphase 1  is not a separate phase. This is the interconnection of later prophase and early metaphase. The chromosomes are arranged on the metaphase plate with the help of a meiotic spindle.

Spindle checkpoint

The spindle checkpoint is a checkpoint that will not allow the phase to go to the next stage of meiosis. The chromosomes got detached with the help of this checkpoint. This leads to some defects in the new cells.

Example

Down syndrome

Down syndrome is a defect caused by the absence of a spindle checkpoint. The gamete dysfunctionality occurs in the syndrome.

Prometaphase 2

Meiosis 2

Four haploid cells are formed in meiosis 2 cell division. This uses the two haploid gametes formed in meiosis 1. In meiosis 2 also, we have phases like prophase 2, prometaphase 2, metaphase 2, anaphase 2, and telophase 2. Meiosis 2 is also called equational division. These phases are the same as in meiosis 1 , but four unique haploid cells are formed in this division. 

What happens in prometaphase 2

The nuclear membrane gets broken down and the spindle is formed. The chromatids get attached to the opposite poles of microtubules. This attachment happens with the help of a kinetochore.

Prometaphase of mitosis

In this phase, the formation of the spindle apparatus happens. In the metaphase plate, the two halves of chromosomes get aligned. In anaphase, this alignment gets released. 

Conclusion

Prometaphase 1 and 2 are the interconnection of later prophase and early metaphase in meiosis 1 and meiosis 2 cell division. This results in the formation of gamete cells. Meiosis 1 and meiosis 2 are the types of meiotic cell division theory. In meiosis, four haploid cells are formed. In meiosis, prometaphase occurs between the metaphase and prophase. It is the interconnection of later prophase and early metaphase. The spindle checkpoint is a checkpoint in which the chromosomes get detached with the help of this checkpoint. This leads to some defects in the new cells. In the prometaphase ,the nuclear membrane breaks down and the spindle is formed. The chromatids get attached to the opposite poles of microtubules. This is what happens in prometaphase 2 also.