A major characteristic that distinguishes meiosis from mitosis is

At the end of mitosis the number of chromosomes in both the parent and the daughter cells are the same - 4N to 2 * 2N; whereas at the end of meiosis the number of chromosomes in the meiotic daughter cells are one-quarter the number of chromosomes of the parent cell - 4N to 2 * 2N to 4 * 1N.

Biology Today and Tomorrow without Physiology (Mi...

ISBN:9781305117396

Author:Cecie Starr, Christine Evers, Lisa Starr

Publisher:Cengage Learning

Organisms grow and reproduce through cell division. In eukaryotic cells, the production of new cells occurs as a result of mitosis and meiosis. These two nuclear division processes are similar but distinct. Both processes involve the division of a diploid cell, or a cell containing two sets of chromosomes (one chromosome donated from each parent).

In mitosis, the genetic material (DNA) in a cell is duplicated and divided equally between two cells. The dividing cell goes through an ordered series of events called the cell cycle. The mitotic cell cycle is initiated by the presence of certain growth factors or other signals that indicate that the production of new cells is needed. Somatic cells of the body replicate by mitosis. Examples of somatic cells include fat cells, blood cells, skin cells, or any body cell that is not a sex cell. Mitosis is necessary to replace dead cells, damaged cells, or cells that have short life spans.

Meiosis is the process by which gametes (sex cells) are generated in organisms that reproduce sexually. Gametes are produced in male and female gonads and contain one-half the number of chromosomes as the original cell. New gene combinations are introduced in a population through the genetic recombination that occurs during meiosis. Thus, unlike the two genetically identical cells produced in mitosis, the meiotic cell cycle produces four cells that are genetically different.

• Mitosis and meiosis are nuclear division processes that occur during cell division.
• Mitosis involves the division of body cells, while meiosis involves the division of sex cells.
• The division of a cell occurs once in mitosis but twice in meiosis.
• Two daughter cells are produced after mitosis and cytoplasmic division, while four daughter cells are produced after meiosis.
• Daughter cells resulting from mitosis are diploid, while those resulting from meiosis are haploid.
• Daughter cells that are the product of mitosis are genetically identical. Daughter cells produced after meiosis are genetically diverse.
• Tetrad formation occurs in meiosis but not mitosis.

1. Cell Division

2. Daughter Cell Number

• Mitosis: Two daughter cells are produced. Each cell is diploid containing the same number of chromosomes.
• Meiosis: Four daughter cells are produced. Each cell is haploid containing one-half the number of chromosomes as the original cell.

3. Genetic Composition

• Mitosis: The resulting daughter cells in mitosis are genetic clones (they are genetically identical). No recombination or crossing over occur.
• Meiosis: The resulting daughter cells contain different combinations of genes. Genetic recombination occurs as a result of the random segregation of homologous chromosomes into different cells and by the process of crossing over (transfer of genes between homologous chromosomes).

4. Length of Prophase

• Mitosis: During the first mitotic stage, known as prophase, chromatin condenses into discrete chromosomes, the nuclear envelope breaks down, and spindle fibers form at opposite poles of the cell. A cell spends less time in prophase of mitosis than a cell in prophase I of meiosis.
• Meiosis: Prophase I consists of five stages and lasts longer than prophase of mitosis. The five stages of meiotic prophase I are leptotene, zygotene, pachytene, diplotene, and diakinesis. These five stages do not occur in mitosis. Genetic recombination and crossing over take place during prophase I.

5. Tetrad Formation

• Mitosis: Tetrad formation does not occur.
• Meiosis: In prophase I, pairs of homologous chromosomes line up closely together forming what is called a tetrad. A tetrad consists of four chromatids (two sets of sister chromatids).

6. Chromosome Alignment in Metaphase

• Mitosis: Sister chromatids (duplicated chromosome comprised of two identical chromosomes connected at the centromere region) align at the metaphase plate (a plane that is equally distant from the two cell poles).
• Meiosis: Tetrads (homologous chromosome pairs) align at the metaphase plate in metaphase I.

7. Chromosome Separation

• Mitosis: During anaphase, sister chromatids separate and begin migrating centromere first toward opposite poles of the cell. A separated sister chromatid becomes known as daughter chromosome and is considered a full chromosome.
• Meiosis: Homologous chromosomes migrate toward opposite poles of the cell during anaphase I. Sister chromatids do not separate in anaphase I.

While the processes of mitosis and meiosis contain a number of differences, they are also similar in many ways. Both processes have a growth period called interphase, in which a cell replicates its genetic material and organelles in preparation for division.

Both mitosis and meiosis involve phases: Prophase, Metaphase, Anaphase and Telophase. Although in meiosis, a cell goes through these cell cycle phases twice. Both processes also involve the lining up of individual duplicated chromosomes, known as sister chromatids, along the metaphase plate. This happens in metaphase of mitosis and metaphase II of meiosis.

In addition, both mitosis and meiosis involve the separation of sister chromatids and the formation of daughter chromosomes. This event occurs in anaphase of mitosis and anaphase II of meiosis. Finally, both processes end with the division of the cytoplasm that produces individual cells.