Meiosis and Mitosis in Onion Root Tip Cells

The kind of cell division in which a single cell duplicates into two identical daughter cells is known as mitosis. Hence, mitosis is a process of cell duplication. Meiosis is the kind of cell division that generates our sex cells, and in this, a single cell duplicates itself twice, thus producing four cells. These cells contain half genetic information. 

Mitosis 

There are five phases in mitosis  

1. Interphase: Here, the DNA in the cell is duplicated which results in two identical full sets of chromosomes. There are two centrosomes outside the nucleus from which microtubules extend. 
2. Prophase: The chromosomes condense into X-shaped structures, where each chromosome is constituted of two sister chromatids, comprising similar genetic evidence.
3. Metaphase: Here, the chromosomes line up along the equator of the cell. Centrioles are present at opposite poles of the cell with the mitotic spindle fibres, which are attached to each of the sister chromatids.
4. Anaphase: The mitotic spindle pulls one chromatid to one pole and the other chromatid to the other pole, separating the sister chromatids.
5. Telophase: During this phase, the chromosomes reach the cell poles, the mitotic spindle disassembles, and the vesicles that comprise components of the original nuclear membrane gather around the two sets of chromosomes.

Meiosis

Meiosis I

1. Interphase: Here, the DNA in the cell is duplicated, and microtubules extend from the two centrosomes outside the nucleus where each centrosome contains a pair of centrioles. 
2. Prophase I: The duplicated chromosomes condense into X-shaped structures that are composed of two sister chromatids comprising similar genetic information.
3. Metaphase I: Here, the chromosomes line up along the equator of the cell. Centrioles are present at opposite poles of the cell with the meiotic spindle fibres which are attached to each of the sister chromatids.
4. Anaphase I: The meiotic spindle separates the sister chromatids by pulling one chromatid to one pole and the other chromatid to the opposite pole. In contrast to mitosis and meiosis II, the sister chromatids stay together in this process.
5. Telophase I and cytokinesis: The chromosomes complete their move to the opposite poles of the cell.

Meiosis II

1. Prophase II: Here, we have two daughter cells, each having 23 chromosomes. In each of the two daughter cells, the chromosomes condense again to form visible X-shaped structures. The membrane around the nucleus dissolves, centrioles duplicate, and the meiotic spindle forms again.
2. Metaphase II: In each of the two daughter cells, the chromosomes line up end-to-end along the equator of the cell. Centrioles are now at opposite poles of each daughter cell; meiotic spindle fibres attach to each of the sister chromatids at each pole.
3. Anaphase II: The sister chromatids are dragged to opposite poles, and the detached chromatids become individual chromosomes due to the action of the meiotic spindle.
4. Telophase II and cytokinesis: The chromosomes finish their move to the opposite poles of the cell, where a full set of chromosomes assemble. A membrane formation takes place but the cell division is incomplete without another round of cytokinesis.

Mitosis in Onion Root Tip

Individual DNA molecules or chromosomes contains the genetic information of all organisms. Eight chromosomes are present in onion cells, while forty-six are found in human cells.

C. Nägeli first observed chromosomes in 1842, and Alfred Waldeyer gave them their name in 188. Mitosis is the process of cell division that Walther Flemming named after himself. The root tips of sprouting seeds and bulbs undergo rapid cell division.

When studying mitosis in labs, the root tips of onion, wheat, lentil, barley, and alfalfa are most commonly used for experiments. As root tips are rapidly growing parts of onions, their cells will therefore be in a variety of mitotic stages. 

To see the individual cells of the onion, the onion root tips are squashed and compressed onto microscopic slides. Some specific DNA stains, like Feulgen and Acetocarmine, can be used to visualise the supercoiling of chromosomes taking place at various stages of mitosis in onion root tip cells.

Difference Between Mitosis and Meiosis 

Conclusion 

Mitosis and meiosis are the two types of cell division. Most of the time, people relate cell division to mitosis, whereas meiosis is the kind of cell division that develops egg and sperm cells. The two processes, mitosis and meiosis, are essential for various life processes where, during mitosis, a cell duplicates itself into two identical daughter cells, whereas during meiosis, it divides itself into four similar daughter cells. These processes aid genetic variation by shuffling genes.