Mitosis, the more common form of cell division, plays a role in maintaining the integrity and functionality of somatic cells, ensuring growth, repair, and replacement of damaged or aging cells. On the other hand, meiosis is a specialized division essential for sexual reproduction, generating gametes with reduced chromosome numbers to facilitate genetic diversity. Let us look at their underlying differences.
What Is Mitosis?
Mitosis is a process of cell division in eukaryotic cells, occurring in somatic (non-reproductive) cells, where a single cell divides into two genetically identical daughter cells. This division is essential for growth, development, tissue repair, and maintenance of the organism. Mitosis is responsible for producing cells for various functions, such as replacing damaged or dying cells and allowing for the growth and development of multicellular organisms.
The mitotic process consists of several stages:
- Interphase: This is the phase where the cell prepares for division. It includes three sub-phases – G1 (cell growth), S (DNA synthesis, where the cell duplicates its DNA), and G2 (preparation for mitosis).
- Prophase: Chromosomes, which are composed of DNA and proteins, condense and become visible. The nuclear envelope breaks down, and spindle fibers start to form.
- Metaphase: Chromosomes align along the cell’s equator, known as the metaphase plate.
- Anaphase: Sister chromatids (identical copies of the chromosome) separate and move towards opposite poles of the cell. This ensures that each daughter cell receives an identical set of chromosomes.
- Telophase: Chromatids reach the poles, and new nuclear envelopes form around them, creating two distinct nuclei within the cell.
- Cytokinesis: This is the final stage, where the cell’s cytoplasm divides, and two daughter cells are formed. In animal cells, a contractile ring pinches the cell membrane, creating two separate cells, while in plant cells, a new cell wall forms between the daughter cells.
Also Read: Difference Between Gametic, Zygotic And Sporic Meiosis
What Is Meiosis?
Meiosis is a specialized type of cell division that occurs in sexually reproductive organisms, leading to the formation of gametes (sperm and egg cells) with half the number of chromosomes compared to the parent cell. While mitosis produces two genetically identical daughter cells, meiosis produces four non-identical daughter cells, each with half the number of chromosomes of the parent cell. This reduction in chromosome number is crucial for maintaining the correct number of chromosomes in sexually reproducing organisms.
The process of meiosis consists of two successive divisions: Meiosis I and Meiosis II. Each of these divisions has its set of phases, similar to mitosis:
Meiosis I:
- Prophase I: Chromosomes condense, and homologous chromosomes (chromosomes with the same genes but possibly different alleles) pair up in a process called synapsis. This allows for genetic recombination or crossing-over, where sections of chromatids are exchanged between homologous chromosomes. The nuclear envelope breaks down, and spindle fibers form.
- Metaphase I: Homologous chromosomes align along the metaphase plate.
- Anaphase I: Homologous chromosomes are pulled apart, with one chromosome from each pair going to opposite poles of the cell.
- Telophase I: Chromosomes reach the poles, and the cell undergoes cytokinesis, resulting in two daughter cells, each with half the original chromosome number.
Meiosis II: Meiosis II is similar to mitosis but involves haploid cells produced in Meiosis I.
- Prophase II: Chromosomes condense again in the haploid cells, and spindle fibers form.
- Metaphase II: Chromosomes align along the metaphase plate in each haploid cell.
- Anaphase II: Sister chromatids are pulled apart, and chromatids move towards opposite poles.
- Telophase II: Chromatids reach the poles, and nuclear envelopes reform around them. Cytokinesis occurs, resulting in a total of four non-identical haploid daughter cells.
The end result of meiosis is the production of four haploid cells, each with a unique combination of genetic material due to crossing-over during Prophase I. These haploid cells are gametes, and when they fuse during fertilization, they restore the diploid chromosome number in the resulting zygote.
Also Read: Difference Between Chromatin And Chromatid
Difference Between Mitosis And Meiosis In Tabular Form
| Elements of Comparison | Mitosis | Meiosis |
| Definition | Mitosis is the process of cell division in which the cell divides into two producing a replica, with an equal number of chromosomes in each resulting diploid cell. | Meiosis is the process of cell division in which the numbers of chromosomes are produced by half through separation of homologous chromosomes, producing two haploid cells. |
| Constitution of Chromosome | In mitosis, each chromosome consists of two chromatids united by a centromere. | In meiosis, the two homologous chromosomes form bivalents or tetrads. Each bivalent has four chromatids and two centromers. |
| Takes Place in | Takes place in the somatic cells of the body. | Takes place in the germ cells. |
| Occurrence | Occurs in both sexually as well as asexually reproducing organisms. | Occurs only in sexually reproducing organisms. |
| Number of Division | The cells usually divide only once. | There are normally two cell divisions, the first and second meiotic divisions. |
| Interphase | Interphase occurs prior to each division. | Interface proceeds only in meiosis. It does not occur prior meiosis II. |
| Prophase | Prophase division stage is relatively simple. | Prophase stage is complicated and divides into leptotene, zygotene, pachytene, diplotene and diakinesis. |
| Duration of Prophase | The duration of prophase is short, usually a few hours. | Prophase is relatively longer and may take days. |
| Exchange of Segments | The two chromatids of a chromosome do not exchange segments during prophase. | Chromatids of two homologous chromosomes exchange segments during crossing over. |
| Division of Chromosome | The cell divides only once and the chromosomes also divide only once. | There are two cell divisions but the chromosomes divide only once. |
| Pairing of Chromosome | Pairing of chromosomes does not occur in mitosis. | Pairing or synapsis of homologous chromosomes takes place that is during zygotene of prophase I and continues up to metaphase I. |
| Division of Centromeres | In mitosis, division of the centromeres takes place during anaphase. | In meiosis, there is no division of centromere during anaphase I. However; centromeres divide only during anaphase II. |
| Movement of Chromosomes during Anaphase | Similar chromosomes move towards the opposite poles in anaphase. | Chromosomes that are not similar move towards the opposite poles both in anaphase I and Anaphase II. |
| Spindle Fibers | Spindle fibers disappear completely in telophase. | Spindle fibers do not disappear completely in telophase I. |
| Chromosome Number | Chromosome number remains constant at the end of mitosis. | The chromosome number is reduced from the diploid to the haploid. |
| Takes Part in | Mitosis takes part in healing and repair. | Meiosis takes part in the formation of gametes and maintenance of chromosome number of a species. |
| Chromosome strand | During anaphase chromosomes are single stranded. | Chromosomes are double stranded in anaphase I, but single stranded in anaphase II. |
| Chromatids | The arms of the prophase chromatids are close to one another. | The arms of the chromatids are widely separate in prophase II. |
| Separation of chromosomes | The chromosome separates simultaneously during anaphase. | Short chromosomes separate early; separation of long chromosomes is delayed. |
| Genetic Constitution of daughter cells. | Two chromatids of chromosome are genetically similar. In other words, the genetic constitution of the daughter cells is identical to that of the parent cells. | Two chromatids of chromosome are genetically different due to crossing over. In other words, the genetic constitution of daughter cells differs from that of the parent cell. The chromosomes of the daughter cells usually contain a mixture of maternal and paternal genes. |
Also Read: Difference Between Cytokinesis In Plants And Cytokinesis In Animals
What are the Similarities Between Mitosis and Meiosis?
- Both processes of cell division give rise to more than one cell.
- Both include breakdown of the nuclear membrane.
- Both depend on spindle fibers to move chromosomes around.
- Both involve cytokinesis at the end of division.
- Fundamental events and processes are same in both meiosis and mitosis.
Also Read: Difference Between Mitosis In Plant And Animal Cells