Comparison of Mitosis and Meiosis

Mitosis and Meiosis: Comparison of Purpose

To understand the differences between these two similar-sounding processes of cell division, which is the production of two or more daughter cells from a parent cell, it is important to note the purpose of mitosis and meiosis.

Mitosis and meiosis are both part of the cell division cycle in which the genetic material is divided in a process known as nuclear division.

The purpose of mitosis

Nuclear division may be the shared purpose of mitosis and meiosis, but each has its separate purposes as well. Mitosis has multiple uses in organisms including:

• Making more cells for growth,

• Replacing old, worn out, or damaged cells,

• Asexual reproduction, where organisms produce genetically identical offspring.

Some animals, plants, fungi, and most single-celled organisms can use mitosis for asexual reproduction. If you followed our article on "Heredity" you might remember that asexual reproduction via mitosis produces clones, meaning organisms have the same genetic makeup as their parents. Reproduction via mitosis provides less genetic diversification.

The purpose of meiosis

The purpose of meiosis is to produce gametes (sex cells) in sexually reproducing organisms. Females have egg cells, and males have sperm.

• Egg cells are produced in the ovaries, whereas sperm cells develop in the testes.

The product of meiosis is four haploid daughter cells. These haploid cells are genetically different from the parent cell and contain half the normal chromosome number (n) of typical cells.

When sexual reproduction occurs, the two haploid (n) cells come together to form a zygote, which is diploid and has two sets of chromosomes.

The Stages of Mitosis and Meiosis

The stages of mitosis and meiosis have the same names: prophase, metaphase, anaphase, and telophase, which are all followed by cytokinesis.

In meiosis, two rounds of division take place, so meiosis is split into meiosis I and meiosis II. The names of each stage within meiosis I or II also have an "I or II" placed at the end of their names (i.e., prophase I or prophase II).

_{Figure 1. Steps of mitosis and meiosis. Source: LadyofHats via commons.wikimedia.org}

Interphase

Before the start of mitosis and meiosis, DNA duplication occurs during interphase to prepare for nuclear division.

Prophase

During prophase, in mitosis and meiosis (I & II), the following occur:

1. The nuclear envelope dissolves.

2. The centrosomes begin to migrate towards opposite poles.

3. The production of spindle fibers starts.

4. The chromosomes condense.

In meiosis I of meiosis, however, the homologous chromosomes form a tetrad, consisting of four chromatids, in which the non-identical chromosomes swap genetic material in a process known as crossing over. This does not happen during meiosis II or mitosis.

Metaphase

During metaphase in mitosis and meiosis, chromosomes line up at the metaphase plate. One difference is that, in meiosis I, chromosomes actually line up side-by-side to prepare for the homologous chromosomes to be separated. In mitosis and meiosis II, however, chromosomes line up single file at the plate.

Anaphase

During anaphase in mitosis and meiosis, chromosomes are pulled to opposite poles via the spindle fibers. They are attached at a point on the chromatids known as the kinetochore. During mitosis and meiosis II, sister chromatids are separated. Meiosis II still produces haploid cells, however, because homologous chromosomes are separated during anaphase I of meiosis I.

Telophase

During telophase, the nuclear envelope starts to reform, and chromosomes decondense. A cleavage furrow, the indentation of the cell membrane, begins to form. At the conclusion of telophase in mitosis, the two daughter cells will be diploid and genetically identical to the parent cell. At the end of telophase II in meiosis, there will be four haploid daughter cells.

Summary of Mitosis and Meiosis Comparison

So far, we have gone over some important facts about the similarities and differences between mitosis and meiosis. Below, a figure highlights the nuclear (chromosomal) differences at the end of meiosis and mitosis (Fig. 2) and the table summarizes what we have discussed (Table 1).

Comparison of Mitosis and Meiosis Diagram

Figure 2 Diagram showing basic steps of mitosis and meiosis. Source: StudySmarter Originals.

Mitosis and Meiosis Comparison Table

Lastly, let's make a table to compare mitosis and meiosis!