Introduction

Meiosis is the process through which gametes are produced during cell division. After two divisions, we have four non-identical haploid daughter gametes from a cell with double the normal amount of DNA. Prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis are the six steps that occur within each division. The stages of meiosis will be discussed in this article, as well as their importance in disease. 

Purpose of Using the Onion Flower Bud for Meiosis

The ensuing rearranged daughter nuclei will have a change in chromosome number from diploid to monoploid or haploid. The chromosomes may remain condensed for some time, the nucleolus and nuclear membrane may be reconstituted, and cytokinesis to form two haploid cells may occur.

Meiosis in Onion Bud Cell

  • Meiosis comes from the Greek word meiosis, which means ‘diminution’. It’s a sort of cell division that happens in diploid species’ reproductive tissues and results in haploid gametes
  • Following fertilisation, the chromosomal count is restored. A diploid mother cell produces four haploid daughter cells during meiosis after two rounds of chromosome segregation events, preceded by just one cycle of DNA replication in the S phase
  • Meiosis I (reductional division) and meiosis II (multistep division) are the two stages of this multistep division process (equational division)
  • It is a division cycle that aids in the maintenance of a species’ chromosomal numbers through repeated divisions

Interphase

The cell’s DNA duplicates, resulting in two complete sets of identical chromosomes. Two centrosomes, each with a pair of centrioles, are located outside the nucleus and essential for cell division. Microtubules protrude from these centrosomes during the interphase period.

Stages of meiosis  I

The two daughter cells contain half as many chromosomes at the end of this phase. Because of the crossing over of homologous chromosomes at prophase I and the subsequent independent arrangement of chromosomes at anaphase I due to their random alignment at metaphase I, each cell is genetically non-identical.

Prophase I

In this stage, the chromosomes condense and move closer to the centre of the cell. it consists of five exclusive sub-stages:

  • Leptotene:

In this case, homologous chromosomes replicate.

  • Zygotene:

Synapsis between homologous chromosomes begins.

  • Pachytene: 

The sister chromatids separate; however, the homologous chromosomes remain attached.

  • Diplotene

The two homologous chromosomes move apart and disintegrate between the chromosomal arms.

  • Diakinesis: 

The condensation of chromosomes stops at this level, and the chiasmata are visible below an electron microscope. The nucleolus and the nuclear envelope disappear, and the centrosome moves towards the equator.

Metaphase I

The homologous chromosomes that contain two different alleles for every gene line up on the metaphase plate to be separated.

Anaphase I

The separated chromosomes are pulled closer to the centrioles on either side of the cell.

Telophase I

The chromosomes are completely pulled aside, and new nuclear envelope forms.

Four Stages of Meiosis II

Prophase II

The nuclear envelope disintegrates, and centrioles develop in this stage.

Metaphase II

The chromosomes line up on the metaphase plate, and chromatids align on either side of the metaphase plate.

Anaphase II

The sister chromatids separate.

Telophase II

The cell divides into two, and a new nuclear envelope surrounds the chromosomes.

Conclusion

Meiosis is a type of cell division in which the number of chromosomes is cut in half, resulting in four haploid cells that are genetically separate from the parent cell. All sexually reproducing single-celled and multicellular eukaryotes, such as animals, plants, and fungus, go through this process. Aneuploidy is the most common genetic cause of developmental problems, while errors in meiosis are the major known cause of miscarriage. DNA replication is followed by two rounds of cell division in meiosis, resulting in four daughter cells with half the number of chromosomes as the parent cell. Meiosis I and Meiosis II are the two distinct meiotic divisions.